Do lunar rhythms have impact on human biology, if so, how?

I'm approaching this question from the circadian rhythm perspective. A circadian rhythm is a 24 hour cycle. While doing research on deep sea circadian rhythms, I found this abstract which seemed to imply that there are some kinds of lunar rhythms (about a month long cycle). Lunar Rhythms in the Deep Sea: Evidence from the Reproductive Periodicity of Several Marine Invertebrates:

While lunar rhythms are commonly documented in plants and animals living in terrestrial and shallow-water environments, deep-sea organisms have essentially been overlooked in that respect.

What do the authors mean by the lunar rhythms? The roughly month long menstrual cycle, or are there other ways that the moon actually influences animal/human biology?

The moon doesn't have a direct effect on metabolism. Nor does it affect menstruation (an archaic theory existed which claimed so!!). The lunar effects are due to its gravitational field which is known to affect tides (Spring tides and neap tides). Even on a daily basis if you might have observed the sea advances into the beach in the night and recedes in the day. This effect is also because of the lunar gravity.

The abstract of the article, that you mentioned, says that moonlight may have some effect on certain organisms; I am highly skeptical about that.

I think it is just the tidal patterns that might affect the behavior of marine/coastal organisms. I am also slightly skeptical about whether the currents produced by lunar gravitation would be deep enough to affect benthic life. In that case even the heating effect of the sun can produce sea currents. Perhaps it can also produce an upward current because of differential heating.

Successful DNA replication in cyanobacteria depends on the circadian clock

A new study from the University of Chicago has found that the photosynthetic bacterium Synechococcus elongatus uses a circadian clock to precisely time DNA replication, and that interrupting this circadian rhythm prevents replication from completing and leaves chromosomes unfinished overnight. The results, published online on May 10 in Proceedings of the National Academy of the Sciences, have implications for understanding how interrupted circadian rhythms can impact human health.

Circadian rhythms are the internal 24-hour clock possessed by most organisms on earth, regulating a diversity of biological functions including sleep/wake cycles, hormone production, digestion and body temperature. In humans, disruptions to the circadian rhythm &mdash such as working a shift-work job or experiencing frequent jet lag &mdash have been associated with an array of health problems, including obesity, cardiovascular and immune dysfunction, mood disorders and even cancer.

&ldquoIn most species we&rsquove studied, if the circadian rhythm is disrupted or permanently changed, it&rsquos bad for the animal&rsquos health, but no one has really been able to explain what goes wrong if your clock is in the wrong state all the time,&rdquo said senior author Michael Rust, PhD, Associate Professor of Molecular Genetics and Cell Biology at UChicago. &ldquoThis cyanobacterial system is exciting because it gives us a chance to answer these mechanistic questions about how circadian rhythms are contributing to the health of an organism.&rdquo

Despite the large evolutionary gap between humans and cyanobacteria, these tiny organisms can provide insights into critical cellular functions such as DNA replication. &ldquoThe evidence suggests that circadian rhythms have evolved multiple times among different species, so there must be something very fundamental and important that&rsquos shared among these different species,&rdquo said first author Yi Liao, a postdoctoral scholar in Rust&rsquos lab. &ldquoDNA replication is also a fundamental process, shared across species, which gave us a clue that it might be regulated by this clock.&rdquo

The investigators were particularly interested in studying this process due to its lengthiness. &ldquoSome things are better to do during the day, like photosynthesis, while others are better at night, like fixing nitrogen,&rdquo said Rust. &ldquoBut DNA replication takes three to four hours to replicate the entire genome, so there&rsquos a fundamental need to predict the future. You commit to doing this thing and you don&rsquot know what the conditions will be like a few hours later. It seemed like maybe this process would use circadian rhythms to &lsquopredict&rsquo the right time to start replication to ensure that it finishes during an optimal window of time.&rdquo

Combining time-lapse fluorescent microscopy, mathematical modeling, molecular genetics and biochemical approaches, Liao and Rust were able to track DNA replication initiation, completion, and failures in bacteria exposed to different illumination patterns, including constant light, normal light/dark cycles and cycles with unexpected periods of darkness.

They found that the circadian clock creates rhythms in DNA replication even in the absence of environmental cues, such as the rising and setting sun. DNA replication typically begins when the clock state corresponds to the morning, and is suppressed when the clock predicts the arrival of night. However, when the internal clock of the bacteria predicts morning but the external environment unexpectedly becomes dark, ongoing replication can&rsquot be completed the replication machinery disassembles, leaving cells with incomplete chromosomes.

&ldquoMany things are regulated by the circadian clock, but it is striking that it matters so much for DNA replication,&rdquo said Rust. &ldquoIf the clock is in the wrong state, it&rsquos the difference between completing the replication event, or the replication machinery falling apart completely.&rdquo

These results, Liao says, open up even more questions. &ldquoWhat is the fate of these unfinished chromosomes? Does this lead to mutations?&rdquo he said. &ldquoMaybe this is a major driving force in the evolution of the circadian clock &mdash you want to avoid damaged DNA and unfinished chromosomes, so the clock has evolved multiple times in history to prevent those things from happening.&rdquo

In a post-Industrial Revolution society, surrounded by artificial lights that can be turned on and off at will, these results could have implications for how circadian rhythms impact human health and why extensive disruptions can be so damaging.

&ldquoOne question that we still need to answer is whether or not this failure to complete DNA replication leads to mutation and genomic instability,&rdquo said Rust. &ldquoOrganisms may experience unexpected darkness on occasion, but their clocks get very strong signals from the cycle of the sun rising and setting. In humans, where we can control the illumination of our environment and ignore the sun, we know there are changes in the circadian rhythm and we know it causes problems, but it&rsquos not clear where those problems come from. We&rsquore trying to put our finger on a molecular mechanism for what might be the biggest problem if your circadian clock is in the wrong state.&rdquo

The study, &ldquoThe circadian clock ensures successful DNA replication in cyanobacteria,&rdquo was supported by the Howard Hughes Medical Institute (Simons Faculty Scholar award) and the NIH (R01-GM107369).

Pollution going multimodal: the complex impact of the human-altered sensory environment on animal perception and performance

Anthropogenic sensory pollution is affecting ecosystems worldwide. Human actions generate acoustic noise, emanate artificial light and emit chemical substances. All of these pollutants are known to affect animals. Most studies on anthropogenic pollution address the impact of pollutants in unimodal sensory domains. High levels of anthropogenic noise, for example, have been shown to interfere with acoustic signals and cues. However, animals rely on multiple senses, and pollutants often co-occur. Thus, a full ecological assessment of the impact of anthropogenic activities requires a multimodal approach. We describe how sensory pollutants can co-occur and how covariance among pollutants may differ from natural situations. We review how animals combine information that arrives at their sensory systems through different modalities and outline how sensory conditions can interfere with multimodal perception. Finally, we describe how sensory pollutants can affect the perception, behaviour and endocrinology of animals within and across sensory modalities. We conclude that sensory pollution can affect animals in complex ways due to interactions among sensory stimuli, neural processing and behavioural and endocrinal feedback. We call for more empirical data on covariance among sensory conditions, for instance, data on correlated levels in noise and light pollution. Furthermore, we encourage researchers to test animal responses to a full-factorial set of sensory pollutants in the presence or the absence of ecologically important signals and cues. We realize that such approach is often time and energy consuming, but we think this is the only way to fully understand the multimodal impact of sensory pollution on animal performance and perception.

1. A multimodal view of sensory pollution

Anthropogenic activities are increasingly affecting the welfare and reproductive success of free-ranging animals [1–3]. Humans emit chemical and physical stimuli into the environment that are received through a range of sensory modalities. These anthropogenic stimuli can decrease animal survival and reproductive success and may ultimately alter populations and ecological communities. To understand and mitigate the effect of these stimuli, it is crucial to study the mechanisms underlying the sensory reception of these pollutants, termed sensory pollution [3–6]. High levels of anthropogenic acoustic noise, for instance, can mask acoustic communication. Chemical emission on the other hand can impair olfactory orientation [5–7]. However, anthropogenic activities often produce stimuli in multiple modalities simultaneously, like the joint emission of acoustic and chemical pollutants by automobile traffic. Furthermore, perception itself is multimodal, and animals sometimes respond in a complex way to the combination of cues from different modalities [8–11]. Finally, sensory pollutants can affect an animal's behaviour as well as its endocrinology. These responses are known to feed back into perceptual and cognitive processes, which further complicate predictions of the potential impact of anthropogenic activities on animal behaviour and reproductive success. We therefore propose an integrated approach to fully understand the multimodal nature of sensory pollution (figure 1). This approach allows us to address how pollutants can disturb animals and interfere with the processing of important signals and cues, how pollutants can affect processes across different modalities, and how the combination of pollutants from different modalities may affect animal performances.

Figure 1. Multimodal approach to understand the environmental impact on animal perception and performance. (a) Animals can receive all sorts of environmental stimuli, such as light, sounds or chemicals, with a variety of sensors found in the peripheral part of their nervous system. These sensors pass on the received information to the central nervous system for higher level processing in different perceptual and cognitive areas. Environmental stimuli can contain relevant information for an animal, e.g. acoustic signals, or irrelevant information, e.g. acoustic noise (arrow widths do not correspond to amount of processed information). When central processing reaches a decision, a behavioural and/or endocrinal response will follow. Complex interactions between and within reception, processing and response determine the impact of the multimodal environment on animals. (b) Example of how environmental conditions can interfere with the perception of multimodal signals and cues. Two stimuli differing in physical form (e.g. a sound or light) that are simultaneously produced by a source travel with different speeds to a receiver who has to extract the relevant information from the two perceptual streams against a background of environmental noise. For example, a male frog produces an acoustic signal, but at the same time generates cues in other sensory modalities, such as vibrations on the water surface. These multimodal components arrive at the receiver at different times (ΔAT). Perceptual processing involves comparing information across modalities. Receivers must bind different sensory components to the same source across time and space. Unimodal noise, e.g. sounds of other calling males, can interfere with multimodal perceptual binding. Sensory interference can also be multimodal, e.g. wind-induced leaf movements, which simultaneously result in acoustic noise and substrate-borne vibrations.

Whether and how animals are affected by sensory pollution depends on overlap in time and space between stimuli exposure and behavioural activity [2–4]. We will first address how anthropogenic pollutants covary in time and space and how this compares to natural variation in environmental sensory conditions. Next, we will discuss how multimodal signals and cues are produced, what sort of information they contain and how animals perceptually process relevant and irrelevant environmental information. Finally, we will describe the ways in which covariance in anthropogenic sensory conditions can interfere with the processing of signals and cues, how pollutants disturb animals by affecting endocrinology and how animals respond by adjusting their behaviour. We will end our review by outlining how we think multimodal sensory pollution should be addressed and list some of the most important outstanding issues.

2. Environmental sensory conditions and covariance among modalities

Animal sensory systems often operate under challenging conditions and are under strong selection from the environment [12]. How does the sensory environment change across time and space for different modalities? How have animals adapted to these changes? And how do human activities affect the sensory environment? Conditions can often correlate across sensory modalities, but we have little data on actual covariance levels in time and space for natural as well as human-impacted environments.

(a) Temporal and spatial variation in natural sensory conditions

Environmental conditions can show large temporal and spatial fluctuations and often covary across modalities (table 1). Ambient light levels, for example, quickly rise with dawn, rapidly drop at dusk and typically correlate with fluctuations in acoustic background levels caused by biotic activity [13,14,16]. Daily and seasonal changes in climate conditions, such as temperature and wind, can also result in concordant patterns across modalities [17,27]. Wind, for instance, can result in higher noise levels, more substrate vibrations and increased visual motion, thus simultaneously affecting multiple senses [28–30]. Multimodal covariance may also occur across space. A fast-flowing stream will be much noisier as well as turbid compared to a slow-flowing river, resulting in covariance of sound and light levels between these two habitat types.

Table 1. Examples of covariance in light, sound and chemical levels from natural and anthropogenic impacted environments.

(b) Covariance in anthropogenic sensory pollutants

High levels of chemical and acoustic emission as well as light pollution typically characterize industrial areas, urban city centres and multi-lane highways. Humans can also alter multiple sensory conditions more indirectly. For example, high phosphate levels in the aquatic environment can increase algae growth, and thus affects both the chemical, as well as the visual environment (table 1, [24]). Sensory pollution can occasionally be biased to particular modalities. Remote terrestrial drilling stations for the gas industry, for example, generate high levels of acoustic noise, but relatively low levels of light pollution [31,32]. Bicycle paths, pedestrian areas or long-term parking lots on the other hand are sometimes associated with high levels of light pollution, but low levels of other pollutants [33,34]. Cases in which types of sensory pollution occur independently provide the opportunity to obtain independent correlational data between pollutant and animal performance [31,34].

Sensory pollution also shows temporal fluctuations. Highway noise levels can be higher during the day than at the night and traffic sounds transmit further on cold spring days compared to warm days later on [14]. Artificial light pollution on the other hand is mainly a nocturnal problem [15,34]. Peak levels in noise and light pollution may therefore not overlap in time, but we should keep in mind that nocturnal urban noise and light levels are still substantially higher when compared with natural conditions, in particular in temperate habitats (table 1, [14,33]).

3. Production and perception of multimodal signals and cues under natural conditions

Animals rely on multiple senses to orient and to communicate. These senses can pick up stimuli emitted intentionally (signals) or unintentionally (cues). How signals and cues of different modalities are produced, transmitted and received has important consequences for environmental selection pressures, such as sensory conditions, that act on the behaviour and physiology of animals [8,35,36].

(a) Multimodal signals produced by animal displays

Animals have evolved elaborate displays to attract mates, fend off rivals or deter predators. Most of these displays generate stimuli that can be perceived with a wide variety of sensory modalities [8,35,36]. Sound production often involves inflation and deflation of morphological structures, like the vocal pouch of grouse or vocal sac of frogs, and as a consequence provides a synchronized multimodal display consisting of visual and acoustic components [37–39]. Sexual displays can also combine components that are independently produced, such as fish using body coloration together with pheromones, or spiders drumming vibrations with one leg and waving colourful tufts with another [24,40].

(b) Multimodal cues produced by predators and prey

Animals also emit stimuli detectable through multiple senses that do not serve themselves, but their predators or prey. A mouse rustling among leaves produces acoustic and visual cues that can aid predatory owls [41]. Vibrations combined with the flow of warm air produced by foraging cattle provide aphids a multimodal cue to flee from plants [42]. Signal production can also generate unintended cues in a different modality. Frogs that call from water bodies to attract mates induce water surface waves, or ripples, that can be detected by eavesdropping bats that benefit from these relatively slow-travelling prey cues [43].

(c) Multimodal perception and nonlinear effects

Incorporating information from multiple sensory systems can increase perceptual processing and the resulting responses in a linear way [44]. However, multimodal perception often involves more complex processes that may not add-up linearly [44,45]. Many perceptual tasks rely on comparisons of information across sensory systems, for instance, to assess timing between components of multimodal signals and cues [44–47]. Such comparisons rely on the brain to accurately assign different components to the same source, which can be challenging under fluctuating sensory conditions (figure 1b, [46]). Animals tested in psychophysical experiments have been shown to respond in linear as well as nonlinear ways when presented with stimuli from different modalities (see [8,9] for a detailed classification of behavioural responses to multimodal signals and cues). Presenting a stimulus in isolation (e.g. a visual signal) can have no effect on an animal's behaviour, but that same stimulus can modify the response to another stimulus (e.g. an acoustic signal) in a complex way [47]. Multimodal signals and cues can even elicit emergent responses [37,46]. Chickens have been found to ignore chemical and visual warning signals of unpalatable caterpillars when presented in isolation, but were shown to avoid food items when both signals were presented in combination [48].

(d) When do animals rely on multimodal perception?

In general, animals rely on multimodal signals and cues when it increases their chances of detecting important environmental events, when it enhances processing of environmental cues or when it provides them with unique sources of environmental information [9,35,46]. Simultaneously produced components from different modalities arrive with varied time delays at a receiver and can thereby provide unique information on distance to the source (figure 1b, [46]). When multimodal signals or cues provide ambiguous information, animals can ignore information from one modality, or arrive at an intermediate solution [45,49]. For example, when nectar-feeding moths are presented with spatially separated chemical and visual cues they approach the visual ones [49].

(e) Multimodal communication and perceptual interference

Multimodal communication can be affected by environmental sensory conditions [7,12]. Animals relying on multimodal signals may benefit from having a signal component that serves a back-up function when interference levels impair processing in one sensory modality [7]. Torrent frogs living next to noisy streams in the rainforest make sounds and wave their legs at the same time [50]. Perceptual information from the two sensory components can be redundant, for instance, both the acoustic and the visual display allowing the detection or recognition of the signaller. Such redundancy can make multimodal signals robust to fluctuations in sensory conditions [50]. On the other hand, multimodal signals will be more susceptible to environmental interference when animals rely on the comparison between sensory components for unique information, such as for estimating the distance from a signaller (figure 1b). Finally, multimodal signals may suffer from multimodal interference when sensory conditions covary across modalities (figure 1b), for example, when wind generates visual and seismic noise and thereby hampers multimodal perception of a spiders' drumming display [40,51].

4. Multimodal impact of anthropogenic pollution on behaviour and physiology

Anthropogenic pollutants are known to disturb animals and to interfere with perceptual processing of important signals and cues. How sensory pollution affects individuals and how their behaviour changes in response depend on the modalities involved, covariance in sensory pollutants, perceptual mechanisms and response plasticity.

(a) Multimodal disturbance by anthropogenic sensory pollution

Anthropogenic noise and artificial lights are well known to disturb animals and often co-occur. However, most studies to date have focused on the impact of one pollutant, or assessed which pollutant was most predictive of a behavioural or endocrinal response and ignored potential additive effects [15,33]. Traffic noise has been associated with increased stress levels and light pollution has been linked to shifts in circadian rhythms [34,52]. So, both pollutants apparently can thus affect endocrine processes and it would be interesting to assess in more detail how noise and light pollution covary and whether their combined impact is similar, increased, or decreased compared to the impact of each pollutant in isolation (figure 2).

Figure 2. Impact of sensory pollution on animal responses across taxa. Sensory pollution can cause general disturbance of behaviour and endocrinology, or interfere with detection and processing of signals and cues. Sensory pollution can be restricted to a single sensory domain (unimodal), affect processes and responses in a different domain (cross-modal), or arrive at the brain through multiple sensory systems (multimodal). Exposure to anthropogenic noise disturbs blue whales and masks acoustic prey cues used by bats [53,54]. Acoustic noise also disturbs visual signalling in squids and may interfere with visual processing in hermit crabs [55,56]. Combined light and noise pollution may increasingly disturb a robin's song behaviour and anthropogenic noise travelling through air and along the water surface may interfere with multimodal communication in frogs (see also figure 1b). (Online version in colour.)

(b) Multimodal interference by anthropogenic sensory pollution

Anthropogenic pollutants can directly interfere with the detection of signals and cues. Traffic noise is known to mask acoustic signals as well as cues used by a wide range of taxa, including birds, mammals, insects and fish [53,57–59], a process we refer to as unimodal interference (figure 2). Anthropogenic noise can also result in multimodal interference, for example, when sounds induce surface vibrations on a leaf or a water surface, resulting in covarying noise levels that may hamper the use of signals and cues in the acoustic and seismic domain at the same time (figure 2, [51]). Pollution with artificial lights has not been linked to impaired detection of visual signals, but may interfere with the use of spatial cues during navigation [60,61]. Animals also rely on acoustic and olfactory cues for orientation, and covariance levels between sound, light and chemicals may consequently result in multimodal interference with spatial navigation cues [6,19]. Indirect anthropogenic effects on aquatic environments may also provide interesting cases for multimodal interference of visual and chemical signals and cues [36].

(c) Cross-modal interference of anthropogenic pollutants

The processing of irrelevant environmental information in one sensory modality may hinder the processing of information in another modality (figure 2, [11]). Such so-called cross-modal interference has been assumed to be responsible for an impact of anthropogenic acoustic noise on the processing speed by hermit crabs that rely on visual cues to detect a predatory threat [56]. Anthropogenic noise has also been linked to an impact on higher level processing of visual information, such as spatial visual orientation [62]. The effect of anthropogenic noise on processing of information in other modalities or cognitive domains can operate via different routes. Noise may induce increased vigilance as a response to a decreased ability to detect acoustic predatory cues and thereby affect the amount of time spent on a visual task [62,63]. Noise may also limit cognitive attention or reduce perceptual processing capacity [56,64]. Finally, noise may induce endocrinal changes, such as increased stress hormone levels, that can cause an indirect effect of the noise on behaviour or feedback to perceptual and cognitive processes (figure 1). Examples of cross-modal interference of other modalities are lacking as far as we know, but a recent study on moths suggests that light pollution may reduce responses to ultrasonic bat calls [65].

(d) Multimodal and cross-modal behavioural responses

Animals are well known to adjust their behaviour in response to interference from sensory pollutants. Some birds can almost instantly change their songs when exposed to noise [66,67]. Whether multimodal signals show similar behavioural flexibility in response to multimodal interference is not known [68]. However, anthropogenic pollutants have been shown to have cross-modal impacts on signalling [55,69]. Noise-exposed squids and chemical-polluted fish change their visual signals, whereas light-exposed birds adjust their acoustic signals [34,55]. These signal adjustments probably reflect a disturbing impact of sensory pollution on endocrinology, e.g. through a link with stress hormones or an impact on circadian rhythms (figure 2). Nevertheless, these examples illustrate that anthropogenic pollution can have consequences for selection pressures acting on signals from different modalities.

5. Anticipating nonlinear impact of multimodal sensory pollution

There is limited experimental data showing how the combination of sensory pollutants alters the behaviour and physiology of animals. Do pollutants enhance or mitigate each other's impact? What happens when one sensory pollutant interferes with signal or cue detection, while another sensory pollutant disturbs an animal, increasing its stress levels? We realize that such questions require extensive testing of animals in a series of stimulus combinations. For example, the full-factorial combination between relevant signals and cues and irrelevant pollutants arriving through two sensory systems results in 16 different experimental treatments (e.g. modality A: signal (yes/no) × pollutant (yes/no) = 4 treatments modality A × B = 16 treatments). Nevertheless, we hope to have provided the conceptual background to encourage researchers to start addressing some of the most interesting outstanding issues.

(a) Additive effects of multimodal sensory pollution

To our knowledge, only one study with hermit crabs addressed multimodal sensory pollution and that study found that anti-predator response was affected most when crabs were exposed to boat noise and boat lights simultaneously [56]. Future studies should aim to address whether the combination of sensory pollutants can have additive, linear or nonlinear, impacts on animal behaviour and physiology by using a full-factorial design in which each pollutant is also tested in isolation.

(b) Modulation effects between sensory pollutants

Sensory pollutants may have a modulating effect on each other via multiple routes (figure 1). A pollutant may not affect behaviour when presented in isolation, but can enhance or reduce the behavioural impact of a pollutant from another modality. These modulation effects can be mediated via an endocrine route, where the modulating pollutant increases stress hormone levels that consequently increase the behavioural impact of the other pollutant. Disentangling different modulation routes again requires testing animals on the full-factorial combination of signals, cues and sensory pollutants.

(c) Emergent multimodal sensory pollution

One of the most interesting outstanding questions in this field concerns the possible impacts of anthropogenic activities that emerge only when sensory pollution is multimodal. Evidence of such hidden impacts would not be found when sensory pollutants are tested in isolation, but could have a substantial effect on animal performances and ultimately on populations or even whole ecosystems considering the potentially high levels of covariance among sensory pollutants.

7. Conclusion and final remarks

The environment is filled with stimuli differing in physical forms, and animals have evolved a variety of sensory systems to make sense of this multimodal world. Likewise, pollution is not restricted to a particular modality. We argue that we need an integrated multimodal approach to appreciate the full ecological impact of human activities on animal performance and perception. We have outlined how anthropogenic stimuli from multiple modalities can co-occur in time and space, and how, across time and space, we need a detailed assessment of multimodal covariance levels to assess potential impact. We have described unimodal, cross-modal and multimodal impacts of sensory pollutants on animal behaviour and physiology, and argue that additive effects can become increasingly complex. We describe sensory disturbance and interference, using examples from a wide range of taxa and sensory domains and think that these concepts are widely applicable to other cases. Recent years have seen a wide body of literature addressing the importance of multimodality in understanding the sensory ecology of animal behaviour. We now add sensory pollution to the concept of multimodality and, in doing so, invoke a number of interesting, outstanding issues that we think should receive considerable attention in the years to come.

Biotechnology, synthetic biology keys to humans colonizing other planets

Over the last 12,000 years or so, human civilization has noticeably reshaped the Earth’s surface. But changes on our own planet will likely pale in comparison when humans settle on other celestial bodies. While many of the changes on Earth over the centuries have been related to food production, by way of agriculture, changes on other worlds will result, not only from the need for on-site production of food, but also for all other consumables, including air.

As vital as synthetic biology will be to the early piloted missions to Mars and voyages of exploration, it will become indispensable to establish a long-term human presence off-Earth, namely colonization. That’s because we’ve evolved over billions of years to thrive specifically in the environments provides by our home planet.

Our physiology is well-suited to Earth’s gravity and its oxygen-rich atmosphere. We also depend on Earth’s magnetic field to shield us from intense space radiation in the form of charged particles. In comparison, Mars currently has no magnetic field to trap particle radiation and an atmosphere that is so thin that any shielding against other types of space radiation is negligible compared with the protection that Earth’s atmosphere affords. At the Martian surface, atmospheric pressure never gets above 7 millibars. That’s like Earth at an altitude of about 27,000 m (89,000 ft), which is almost the edge of space. And it’s not like the moon is a better option for us since it has no atmosphere at all.

Living off the land: Creating Earth-like environments away from Earth

Living anywhere in our Solar System beyond Earth will require the same level of protection that an astronaut needs while walking in space. A human-friendly environment must be provided to sustain life, and for long-term human presence that environment must be sustainable. In contrast to short flights into low-Earth orbit, or brief visits to the Moon, space colonists will not be able to rely on deliveries of air, water, and food from Earth instead they will have to live off the land. They’ll have to create Earth-like environments with consumables derived from local materials and recycled the way that air, water, and things that we eat are replenished on our home world.

The lack of technology for such sustainable life support systems is a major factor underlying criticism of human space exploration. And it’s not the only factor. There’s also the high cost of human space flight and the substantial risk to human life. Weighed against the staggering advances in computers, robots, and nanotechnology, the argument for sending astronauts to explore space instead of robot probes seems weak, except when one more issue is added to the equation: extinction insurance against planet-wide disasters caused either by nature, or by our own negligence.

In a newly published book, a very original take on the human future and spaceflight, Louis Friedman, a space policy expert and astronautical engineer, embraces both the pro-human and pro-robot perspective. He does this by arguing that off-world colonization will be needed, and therefore accomplished soon, to assure long-term survival of humanity, with Mars as the chosen location for our second home. But when it comes to exploration deeper into space, Friedman believes that we’ll opt to leave that task to our robot emissaries. The reason, which he outlined in an interview with this writer for Discover Magazine, is that technology — including biotechnology that will enable uploading of the visual, audio, and other sensory experiences of our robot explorers to the human brain — will make virtual travel to distant locations better than the real thing, so why put the fragile human body at so much risk?

How much risk is acceptable may be a matter of opinion, but in addition to making a virtual space exploration experience, biotechnology also could reduce the risk to humans who do choose to travel through space physically. In a new paper published outline in the Journal of the Royal Society, University of California, Berkeley aerospace engineer and synthetic biology researcher Amor Menezes suggested six key challenges to establishing a human space presence that could be addressed with synthetic biology.

Synthetic biology and the challenges of space colonization

The first challenge, Menezes and his colleagues explain, is resource utilization. Unlike the Pilgrims on the shores of America, early colonists on the Moon or Mars will not be able to get their dinner by going fishing, but they could make the lunar or Martian dirt into soil for growing plants. The Moon has water in the form of ice that they could melt and both water and the lunar rocks contain oxygen that can be drawn out through electrochemical reactions. Rather than discard the carbon dioxide that humans exhale as is done on spacecraft, colonists could use the waste gas as a carbon source for making food. We already have organisms that do this. They include plants and photosynthetic bacteria, but genetic engineering has been making the carbon fixation process to create food more efficient, and future modification could be tailored to make optimize photosynthesis for the dirt and environments of the Moon and Mars. In addition to food production, organisms can also be engineered to convert Martian and lunar materials into fuel that could be used for rockets, and finally the organisms could be used to process waste.

In addition to using locally derived resources, space colonists will need to engage in massive manufacturing. Menezes believes that organisms could be engineered to produce biocement, biopolymers, adhesives, and other building materials. By recycling air and water. processing solid wastes, and producing food, genetically modified organisms could also play a central role in life support systems, which the paper lists as the third challenge for a long-term human space presence.

As for the fourth challenge, the researchers discuss space medicine and human health applications. Examples of how genetic engineering can help in this area include onsite synthesis of drugs, a capability that will be vital to colonizations, since drugs are vulnerable to radiation, making the prospect of transporting medicines from Earth unattractive. At the same time, modified organisms might also be developed to create radiation-resistant clothing and other bioshielding material.

Space cybernetics is the fifth challenge. For reasons similar to the drug manufacture issue, space colonists will be better off making their own electronics rather than depending on electronics shipped from Earth, and biosynthetic approaches could be the right tactic.

The final challenge, one that Menezes and the team admits is the most difficult, is called terraforming. Whether on the Moon, Mars, or even an asteroid, living inside a pressurized module won’t be satisfying for more than a short bout. For long-term residence, humans will need environments that look and feel natural, with plenty of trees, parkland, and rivers and streams in order to thrive.

The process of converting an entire planet like Mars or Venus into a world with a breathable atmosphere and a comfortable temperature is called terraforming. Scientists think that it could be technically possible, but terraforming an entire Mars-like world would probably take centuries and possibly even millennia. For this reason, space colonization proponents are also considering a less ambitious goal known as paraterraforming, basically terraforming but on a limited area of another world. On the Moon, for instance, a large crater, such as the 21 kilometer wide Shackelton crater on the Moon’s south pole, could be sealed with a dome and the inner environment could be terraformed in just a few years. On Mars, caves could be sealed and terraformed, while a small asteroid could be hollowed out, terraformed on the inside and even spun to create Earth-equivalent gravity. In all of these cases, engineered organisms would be key to the paraformation process. As on Earth, success would be more likely for those willing to start small, and the creation of an Earth-like environment on a small scale would demonstrate that, in the future, it might also be achieved on a planetary scale.

If a long-term human presence on other worlds is the goal, then genetically altered organisms are the key. If this is the case, and if we do decide that extinction insurance makes sense, it would mean that human survival itself depends on the continued development of biotechnology.

David Warmflash is an astrobiologist, physician, and science writer. Follow @CosmicEvolution to read what he’s saying on Twitter.


The idea of introducing daylight saving time (DST) was attractive at the time of candles and gas lamps, as it allowed workers to use sunlight a bit longer during working hours as well as saving employers’ energy for lighting. Much has changed since then. Today, only a small fraction of electricity expenditure actually corresponds to producing light after sunset (in the US, it is about six percent in the residential sector and eight percent in the industrial sector) [1]. Yet, over a quarter of the world population is subjected to the DST shift twice a year, which disrupts both human work and rest schedules and possibly their circadian clock rhythms [2]. DST shifts have been shown to have a measurable effect on electric power consumption, although not necessarily in the intended direction [3,4]. Previous studies have demonstrated that the spring DST shift causes noticeable alterations in human behavior in terms of waking-up time and self-reported alertness, [5] a significant increase in fatal traffic accidents (up to 30 percent on the day of commencing DST), [6] a short-term rise in workplace injuries (5.7 percent after the spring DST shift as employees sleep 40 minutes less on average), [7] and elevated rates of acute myocardial infarction (up by about 3.9 percent) [8]. The study described in [6] and [9] reported conflicting results regarding whether the DST shifts are associated with accident incidence. The study described in [10] found increased mental health- and behavioral health-oriented emergency department visits in certain seasons, but did not obtain conclusive results on whether they could be linked to the DST shifts.

Remarkable progress has been made in the past decade towards understanding the neurology of sleep-wake cycles and circadian rhythms, and how they affect our behavior [11]. Despite these advances, significant gaps remain in our knowledge of how changes in the social clock (DST shifts) interact with the body’s biological clock and impact human health. Recent studies have urged for investigations into the clinical implications of DST shifts on human health [12,13].

The DST shift represents a natural exposure experiment which allows us the unique opportunity of linking health outcomes to an external, state-wide event in the US and Sweden. Earlier analyses of DST shift effects typically examined a single medical condition per study, often with conflicting or inconclusive results [6,9,10]. In addition, these studies often relied on small, disease-specific datasets with thousands of observations from a single country or a single hospital, making it impossible to run phenome-wide screening. In the present study, we used the electronic health records (EHRs) of hundreds of millions of people across two countries, for the purpose of: (1) examining the temporal disease risk dynamics in relationship to DST shifts, and (2) identifying those population strata which manifest health changes linked to DST-related schedule disruption.

How can light pollution exposures be limited

The disappearance of our night skies has largely gone unnoticed as the increasingly urban-based population has never had the opportunity to view a pristine night sky. Activist organizations, like the International Dark Sky Association, are working to preserve dark skies, as well as partnering with cities and municipalities to minimize the light pollution produced by electric light and improve energy efficiency. The good news is that light pollution is reversible. City ordinances and active community efforts have made major impacts in reducing outdoor light pollution and preserving night skies.

There has also been increased advocacy to reduce circadian disruption from light infiltration via smartphones, computers, and indoor artificial light. Steps we can take to reduce our light pollution impacts include: switching light bulbs to warm-colored bulbs or LED lights, making active efforts to turn off unnecessary indoor or outdoor lighting, and protecting our eyes from blue light by using blue light glasses and screen protectors. These efforts not only improve night sky quality, but prevent negative health outcomes associated with increased indoor or outdoor light exposure.

Samantha Tracy is a Masters of Science student in Environmental Health at Harvard School of Public Health. Her concentration is in Environmental Exposure Assessment.

Wei Wu is a graduate student in the Design Studies program at Harvard University Graduate School of Design. Her concentration is Art, Design and the Public Domain.

Cover image: “A Night View Of Jaffna Street” by Muthulingam Tamilnilavan is licensed under CC BY-SA 4.0.


Many of the environmental conditions experienced by humans during spaceflight are very different from those in which humans evolved however, technology such as that offered by a spaceship or spacesuit is able to shield people from the harshest conditions. The immediate needs for breathable air and drinkable water are addressed by a life support system, a group of devices that allow human beings to survive in outer space. [12] The life support system supplies air, water and food. It must also maintain temperature and pressure within acceptable limits and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites is also necessary.

Some hazards are difficult to mitigate, such as weightlessness, also defined as a microgravity environment. Living in this type of environment impacts the body in three important ways: loss of proprioception, changes in fluid distribution, and deterioration of the musculoskeletal system.

On November 2, 2017, scientists reported that significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space, based on MRI studies. Astronauts who took longer space trips were associated with greater brain changes. [13] [14]

In October 2018, NASA-funded researchers found that lengthy journeys into outer space, including travel to the planet Mars, may substantially damage the gastrointestinal tissues of astronauts. The studies support earlier work that found such journeys could significantly damage the brains of astronauts, and age them prematurely. [15]

In March 2019, NASA reported that latent viruses in humans may be activated during space missions, adding possibly more risk to astronauts in future deep-space missions. [16]

Research Edit

Space medicine is a developing medical practice that studies the health of astronauts living in outer space. The main purpose of this academic pursuit is to discover how well and for how long people can survive the extreme conditions in space, and how fast they can re-adapt to the Earth's environment after returning from space. Space medicine also seeks to develop preventive and palliative measures to ease the suffering caused by living in an environment to which humans are not well adapted.

Ascent and re-entry Edit

During takeoff and re-entry space travelers can experience several times normal gravity. An untrained person can usually withstand about 3g, but can blackout at 4 to 6g. G-force in the vertical direction is more difficult to tolerate than a force perpendicular to the spine because blood flows away from the brain and eyes. First the person experiences a temporary loss of vision and then at higher g-forces loses consciousness. G-force training and a G-suit which constricts the body to keep more blood in the head can mitigate the effects. Most spacecraft are designed to keep g-forces within comfortable limits.

Space environments Edit

The environment of space is lethal without appropriate protection: the greatest threat in the vacuum of space derives from the lack of oxygen and pressure, although temperature and radiation also pose risks. The effects of space exposure can result in ebullism, hypoxia, hypocapnia, and decompression sickness. In addition to these, there is also cellular mutation and destruction from high energy photons and sub-atomic particles that are present in the surroundings. [17] Decompression is a serious concern during the extra-vehicular activities (EVAs) of astronauts. [18] Current EMU designs take this and other issues into consideration, and have evolved over time. [19] [20] A key challenge has been the competing interests of increasing astronaut mobility (which is reduced by high-pressure EMUs, analogous to the difficulty of deforming an inflated balloon relative to a deflated one) and minimising decompression risk. Investigators [21] have considered pressurizing a separate head unit to the regular 71 kPa (10.3 psi) cabin pressure as opposed to the current whole-EMU pressure of 29.6 kPa (4.3 psi). [20] [22] In such a design, pressurization of the torso could be achieved mechanically, avoiding mobility reduction associated with pneumatic pressurization. [21]

Vacuum Edit

Human physiology is adapted to living within the atmosphere of Earth, and a certain amount of oxygen is required in the air we breathe. If the body does not get enough oxygen, then the astronaut is at risk of becoming unconscious and dying from hypoxia. In the vacuum of space, gas exchange in the lungs continues as normal but results in the removal of all gases, including oxygen, from the bloodstream. After 9 to 12 seconds, the deoxygenated blood reaches the brain, and it results in the loss of consciousness. [23] Exposure to vacuum for up to 30 seconds is unlikely to cause permanent physical damage. [24] Animal experiments show that rapid and complete recovery is normal for exposures shorter than 90 seconds, while longer full-body exposures are fatal and resuscitation has never been successful. [25] [26] There is only a limited amount of data available from human accidents, but it is consistent with animal data. Limbs may be exposed for much longer if breathing is not impaired. [27]

In December 1966, aerospace engineer and test subject Jim LeBlanc of NASA was participating in a test to see how well a pressurized space suit prototype would perform in vacuum conditions. To simulate the effects of space, NASA constructed a massive vacuum chamber from which all air could be pumped. [28] At some point during the test, LeBlanc's pressurization hose became detached from the space suit. [29] Even though this caused his suit pressure to drop from 3.8 psi (26.2 kPa) to 0.1 psi (0.7 kPa) in less than 10 seconds, LeBlanc remained conscious for about 14 seconds before losing consciousness due to hypoxia the much lower pressure outside the body causes rapid de-oxygenation of the blood. "As I stumbled backwards, I could feel the saliva on my tongue starting to bubble just before I went unconscious and that's the last thing I remember," recalls LeBlanc. [30] The chamber was rapidly pressurized and LeBlanc was given emergency oxygen 25 seconds later. He recovered almost immediately with just an earache and no permanent damage. [31] [32]

Another effect from a vacuum is a condition called ebullism which results from the formation of bubbles in body fluids due to reduced ambient pressure, the steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. [33] Technically, ebullism is considered to begin at an elevation of around 19 kilometres (12 mi) or pressures less than 6.3 kPa (47 mm Hg), [34] known as the Armstrong limit. [17] Experiments with other animals have revealed an array of symptoms that could also apply to humans. The least severe of these is the freezing of bodily secretions due to evaporative cooling. Severe symptoms, such as loss of oxygen in tissue, followed by circulatory failure and flaccid paralysis would occur in about 30 seconds. [17] The lungs also collapse in this process, but will continue to release water vapour leading to cooling and ice formation in the respiratory tract. [17] A rough estimate is that a human will have about 90 seconds to be recompressed, after which death may be unavoidable. [33] [35] Swelling from ebullism can be reduced by containment in a flight suit which are necessary to prevent ebullism above 19 km. [27] During the Space Shuttle program astronauts wore a fitted elastic garment called a Crew Altitude Protection Suit (CAPS) which prevented ebullism at pressures as low as 2 kPa (15 mm Hg). [36]

The only humans known to have died of exposure to vacuum in space are the three crew-members of the Soyuz 11 spacecraft Vladislav Volkov, Georgi Dobrovolski, and Viktor Patsayev. During preparations for re-entry from orbit on June 30, 1971, a pressure-equalisation valve in the spacecraft's descent module unexpectedly opened at an altitude of 168 kilometres (551,000 ft), causing rapid depressurisation and the subsequent death of the entire crew. [37] [38]

Temperature Edit

In a vacuum, there is no medium for removing heat from the body by conduction or convection. Loss of heat is by radiation from the 310 K temperature of a person to the 3 K of outer space. This is a slow process, especially in a clothed person, so there is no danger of immediately freezing. [39] Rapid evaporative cooling of skin moisture in a vacuum may create frost, particularly in the mouth, but this is not a significant hazard.

Exposure to the intense radiation of direct, unfiltered sunlight would lead to local heating, though that would likely be well distributed by the body's conductivity and blood circulation. Other solar radiation, particularly ultraviolet rays, however, may cause severe sunburn.

Radiation Edit

Without the protection of Earth's atmosphere and magnetosphere astronauts are exposed to high levels of radiation. High levels of radiation damage lymphocytes, cells heavily involved in maintaining the immune system this damage contributes to the lowered immunity experienced by astronauts. Radiation has also recently been linked to a higher incidence of cataracts in astronauts. Outside the protection of low Earth orbit, galactic cosmic rays present further challenges to human spaceflight, [43] as the health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure. [44] A NASA-supported study reported that radiation may harm the brain of astronauts and accelerate the onset of Alzheimer's disease. [45] [46] [47] [48] Solar flare events (though rare) can give a fatal radiation dose in minutes. It is thought that protective shielding and protective drugs may ultimately lower the risks to an acceptable level. [49]

Crew living on the International Space Station (ISS) are partially protected from the space environment by Earth's magnetic field, as the magnetosphere deflects solar wind around the earth and the ISS. Nevertheless, solar flares are powerful enough to warp and penetrate the magnetic defences, and so are still a hazard to the crew. The crew of Expedition 10 took shelter as a precaution in 2005 in a more heavily shielded part of the station designed for this purpose. [50] [51] However, beyond the limited protection of Earth's magnetosphere, interplanetary human missions are much more vulnerable. Lawrence Townsend of the University of Tennessee and others have studied the most powerful solar flare ever recorded. Radiation doses astronauts would receive from a flare of this magnitude could cause acute radiation sickness and possibly even death. [52]

There is scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases. [53] Radiation can penetrate living tissue and cause both short and long-term damage to the bone marrow stem cells which create the blood and immune systems. In particular, it causes 'chromosomal aberrations' in lymphocytes. As these cells are central to the immune system, any damage weakens the immune system, which means that in addition to increased vulnerability to new exposures, viruses already present in the body—which would normally be suppressed—become active. In space, T-cells (a form of lymphocyte) are less able to reproduce properly, and the T-cells that do reproduce are less able to fight off infection. Over time immunodeficiency results in the rapid spread of infection among crew members, especially in the confined areas of space flight systems.

On 31 May 2013, NASA scientists reported that a possible human mission to Mars [54] may involve a great radiation risk based on the amount of energetic particle radiation detected by the RAD on the Mars Science Laboratory while traveling from the Earth to Mars in 2011–2012. [40] [41] [42]

In September 2017, NASA reported radiation levels on the surface of the planet Mars were temporarily doubled, and were associated with an aurora 25-times brighter than any observed earlier, due to a massive, and unexpected, solar storm in the middle of the month. [55]

Weightlessness Edit

Following the advent of space stations that can be inhabited for long periods of time, exposure to weightlessness has been demonstrated to have some deleterious effects on human health. Humans are well-adapted to the physical conditions at the surface of the earth, and so in response to weightlessness, various physiological systems begin to change, and in some cases, atrophy. Though these changes are usually temporary, some do have a long-term impact on human health.

Short-term exposure to microgravity causes space adaptation syndrome, self-limiting nausea caused by derangement of the vestibular system. Long-term exposure causes multiple health problems, one of the most significant being loss of bone and muscle mass. Over time these deconditioning effects can impair astronauts' performance, increase their risk of injury, reduce their aerobic capacity, and slow down their cardiovascular system. [56] As the human body consists mostly of fluids, gravity tends to force them into the lower half of the body, and our bodies have many systems to balance this situation. When released from the pull of gravity, these systems continue to work, causing a general redistribution of fluids into the upper half of the body. This is the cause of the round-faced 'puffiness' seen in astronauts. [49] [57] Redistributing fluids around the body itself causes balance disorders, distorted vision, and a loss of taste and smell.

A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated in space. [58] On April 29, 2013, scientists in Rensselaer Polytechnic Institute, funded by NASA, reported that, during spaceflight on the International Space Station, microbes seem to adapt to the space environment in ways "not observed on Earth" and in ways that "can lead to increases in growth and virulence". [59] More recently, in 2017, bacteria were found to be more resistant to antibiotics and to thrive in the near-weightlessness of space. [60] Microorganisms have been observed to survive the vacuum of outer space. [61] [62]

Motion sickness Edit

The most common problem experienced by humans in the initial hours of weightlessness is known as space adaptation syndrome or SAS, commonly referred to as space sickness. It is related to motion sickness, and arises as the vestibular system adapts to weightlessness. [63] Symptoms of SAS include nausea and vomiting, vertigo, headaches, lethargy, and overall malaise. [2] The first case of SAS was reported by cosmonaut Gherman Titov in 1961. Since then, roughly 45% of all people who have flown in space have suffered from this condition.

Bone and muscle deterioration Edit

A major effect of long-term weightlessness involves the loss of bone and muscle mass. Without the effects of gravity, skeletal muscle is no longer required to maintain posture and the muscle groups used in moving around in a weightless environment differ from those required in terrestrial locomotion. [ citation needed ] In a weightless environment, astronauts put almost no weight on the back muscles or leg muscles used for standing up. Those muscles then start to weaken and eventually get smaller. Consequently, some muscles atrophy rapidly, and without regular exercise astronauts can lose up to 20% of their muscle mass in just 5 to 11 days. [64] The types of muscle fibre prominent in muscles also change. Slow-twitch endurance fibres used to maintain posture are replaced by fast-twitch rapidly contracting fibres that are insufficient for any heavy labour. Advances in research on exercise, hormone supplements, and medication may help maintain muscle and body mass.

Bone metabolism also changes. Normally, bone is laid down in the direction of mechanical stress. However, in a microgravity environment, there is very little mechanical stress. This results in a loss of bone tissue approximately 1.5% per month especially from the lower vertebrae, hip, and femur. [65] Due to microgravity and the decreased load on the bones, there is a rapid increase in bone loss, from 3% cortical bone loss per decade to about 1% every month the body is exposed to microgravity, for an otherwise healthy adult. [66] The rapid change in bone density is dramatic, making bones frail and resulting in symptoms that resemble those of osteoporosis. On Earth, the bones are constantly being shed and regenerated through a well-balanced system which involves signaling of osteoblasts and osteoclasts. [67] These systems are coupled, so that whenever bone is broken down, newly formed layers take its place—neither should happen without the other, in a healthy adult. In space, however, there is an increase in osteoclast activity due to microgravity. This is a problem because osteoclasts break down the bones into minerals that are reabsorbed by the body. [ citation needed ] Osteoblasts are not consecutively active with the osteoclasts, causing the bone to be constantly diminished with no recovery. [68] This increase in osteoclasts activity has been seen particularly in the pelvic region because this is the region that carries the biggest load with gravity present. A study demonstrated that in healthy mice, osteoclasts appearance increased by 197%, accompanied by a down-regulation of osteoblasts and growth factors that are known to help with the formation of new bone, after only sixteen days of exposure to microgravity. Elevated blood calcium levels from the lost bone result in dangerous calcification of soft tissues and potential kidney stone formation. [65] It is still unknown whether bone recovers completely. Unlike people with osteoporosis, astronauts eventually regain their bone density. [ citation needed ] After a 3–4 month trip into space, it takes about 2–3 years to regain lost bone density. [ citation needed ] New techniques are being developed to help astronauts recover faster. Research on diet, exercise, and medication may hold the potential to aid the process of growing new bone.

To prevent some of these adverse physiological effects, the ISS is equipped with two treadmills (including the COLBERT), and the aRED (advanced Resistive Exercise Device), which enable various weight-lifting exercises which add muscle but do nothing for bone density, [69] and a stationary bicycle each astronaut spends at least two hours per day exercising on the equipment. [70] [71] Astronauts use bungee cords to strap themselves to the treadmill. [72] [73] Astronauts subject to long periods of weightlessness wear pants with elastic bands attached between waistband and cuffs to compress the leg bones and reduce osteopenia. [4]

Currently, NASA is using advanced computational tools to understand how to best counteract the bone and muscle atrophy experienced by astronauts in microgravity environments for prolonged periods of time. [74] The Human Research Program's Human Health Countermeasures Element chartered the Digital Astronaut Project to investigate targeted questions about exercise countermeasure regimes. [75] [76] NASA is focusing on integrating a model of the advanced Resistive Exercise Device (ARED) currently on board the International Space Station with OpenSim [77] musculoskeletal models of humans exercising with the device. The goal of this work is to use inverse dynamics to estimate joint torques and muscle forces resulting from using the ARED, and thus more accurately prescribe exercise regimens for the astronauts. These joint torques and muscle forces could be used in conjunction with more fundamental computational simulations of bone remodeling and muscle adaptation in order to more completely model the end effects of such countermeasures, and determine whether a proposed exercise regime would be sufficient to sustain astronaut musculoskeletal health.

Fluid redistribution Edit

In space, astronauts lose fluid volume—including up to 22% of their blood volume. Because it has less blood to pump, the heart will atrophy. A weakened heart results in low blood pressure and can produce a problem with "orthostatic tolerance", or the body's ability to send enough oxygen to the brain without the astronaut's fainting or becoming dizzy. "Under the effects of the earth's gravity, blood and other body fluids are pulled towards the lower body. When gravity is taken away or reduced during space exploration, the blood tends to collect in the upper body instead, resulting in facial edema and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in orthostatic hypotension." [78]

Disruption of senses Edit

Vision Edit

In 2013 NASA published a study that found changes to the eyes and eyesight of monkeys with spaceflights longer than 6 months. [79] Noted changes included a flattening of the eyeball and changes to the retina. [79] Space traveler's eye-sight can become blurry after too much time in space. [80] [81] Another effect is known as cosmic ray visual phenomena.

. [a] NASA survey of 300 male and female astronauts, about 23 percent of short-flight and 49 percent of long-flight astronauts said they had experienced problems with both near and distance vision during their missions. Again, for some people vision problems persisted for years afterward.

Since dust can not settle in zero gravity, small pieces of dead skin or metal can get in the eye, causing irritation and increasing the risk of infection. [82]

Long spaceflights can also alter a space traveler's eye movements (particularly the vestibulo-ocular reflex). [83]

Intracranial pressure Edit

Because weightlessness increases the amount of fluid in the upper part of the body, astronauts experience increased intracranial pressure. [84] This appears to increase pressure on the backs of the eyeballs, affecting their shape and slightly crushing the optic nerve. [1] [85] [86] [87] [88] [89] This effect was noticed in 2012 in a study using MRI scans of astronauts who had returned to Earth following at least one month in space. [90] Such eyesight problems could be a major concern for future deep space flight missions, including a crewed mission to the planet Mars. [54] [85] [86] [87] [88] [91]

If indeed elevated intracranial pressure is the cause, artificial gravity might present one solution, as it would for many human health risks in space. However, such artificial gravitational systems have yet to be proven. More, even with sophisticated artificial gravity, a state of relative microgravity may remain, the risks of which remain unknown. [92]

Taste Edit

One effect of weightlessness on humans is that some astronauts report a change in their sense of taste when in space. [93] Some astronauts find that their food is bland, others find that their favorite foods no longer taste as good (one who enjoyed coffee disliked the taste so much on a mission that he stopped drinking it after returning to Earth) some astronauts enjoy eating certain foods that they would not normally eat, and some experience no change whatsoever. Multiple tests have not identified the cause, [94] and several theories have been suggested, including food degradation, and psychological changes such as boredom. Astronauts often choose strong-tasting food to combat the loss of taste.

Additional physiological effects Edit

Within one month the human skeleton fully extends in weightlessness, causing height to increase by an inch. [57] After two months, calluses on the bottoms of feet molt and fall off from lack of use, leaving soft new skin. Tops of feet become, by contrast, raw and painfully sensitive, as they rub against the handrails feet are hooked into for stability. [95] Tears cannot be shed while crying, as they stick together into a ball. [96] In microgravity odors quickly permeate the environment, and NASA found in a test that the smell of cream sherry triggered the gag reflex. [94] Various other physical discomforts such as back and abdominal pain are common because of the readjustment to gravity, where in space there was no gravity and these muscles could freely stretch. [97] These may be part of the asthenization syndrome reported by cosmonauts living in space over an extended period of time, but regarded as anecdotal by astronauts. [98] Fatigue, listlessness, and psychosomatic worries are also part of the syndrome. The data is inconclusive however, the syndrome does appear to exist as a manifestation of the internal and external stress crews in space must face. [ citation needed ]

Research Edit

The psychological effects of living in space have not been clearly analyzed but analogies on Earth do exist, such as Arctic research stations and submarines. The enormous stress on the crew, coupled with the body adapting to other environmental changes, can result in anxiety, insomnia and depression. [99]

Stress Edit

There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance. [100] Cosmonaut Valery Ryumin, twice Hero of the Soviet Union, quotes this passage from The Handbook of Hymen by O. Henry in his autobiographical book about the Salyut 6 mission: "If you want to instigate the art of manslaughter just shut two men up in an eighteen by twenty-foot cabin for a month. Human nature won't stand it." [101]

NASA's interest in psychological stress caused by space travel, initially studied when their crewed missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance while under public scrutiny, as well as isolation from peers and family. On the ISS, the latter is still often a cause of stress, such as when NASA Astronaut Daniel Tani's mother died in a car accident, and when Michael Fincke was forced to miss the birth of his second child. [ citation needed ]

Sleep Edit

The amount and quality of sleep experienced in space is poor due to highly variable light and dark cycles on flight decks and poor illumination during daytime hours in the spacecraft. Even the habit of looking out of the window before retiring can send the wrong messages to the brain, resulting in poor sleep patterns. These disturbances in circadian rhythm have profound effects on the neurobehavioural responses of the crew and aggravate the psychological stresses they already experience (see Fatigue and sleep loss during spaceflight for more information). Sleep is disturbed on the ISS regularly due to mission demands, such as the scheduling of incoming or departing space vehicles. Sound levels in the station are unavoidably high because the atmosphere is unable to thermosiphon fans are required at all times to allow processing of the atmosphere, which would stagnate in the freefall (zero-g) environment. Fifty percent of space shuttle astronauts took sleeping pills and still got 2 hours less sleep each night in space than they did on the ground. NASA is researching two areas which may provide the keys to a better night's sleep, as improved sleep decreases fatigue and increases daytime productivity. A variety of methods for combating this phenomenon are constantly under discussion. [102]

Duration of space travel Edit

A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment. [103] While Skylab's three crews remained in space 1, 2, and 3 months respectively, long-term crews on Salyut 6, Salyut 7, and the ISS remain about 5–6 months, while MIR expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak different languages. First-generation space stations had crews who spoke a single language, while 2nd and 3rd generation stations have crews from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way.

The sum of human experience has resulted in the accumulation of 58 solar years in space and a much better understanding of how the human body adapts. In the future, industrialisation of space and exploration of inner and outer planets will require humans to endure longer and longer periods in space. The majority of current data comes from missions of short duration and so some of the long-term physiological effects of living in space are still unknown. A round trip to Mars [54] with current technology is estimated to involve at least 18 months in transit alone. Knowing how the human body reacts to such time periods in space is a vital part of the preparation for such journeys. On-board medical facilities need to be adequate for coping with any type of trauma or emergency as well as contain a huge variety of diagnostic and medical instruments in order to keep a crew healthy over a long period of time, as these will be the only facilities available on board a spacecraft for coping not only with trauma but also with the adaptive responses of the human body in space.

At the moment only rigorously tested humans have experienced the conditions of space. If off-world colonization someday begins, many types of people will be exposed to these dangers, and the effects on the very young are completely unknown. On October 29, 1998, John Glenn, one of the original Mercury 7, returned to space at the age of 77. His space flight, which lasted 9 days, provided NASA with important information about the effects of space flight on older people. Factors such as nutritional requirements and physical environments which have so far not been examined will become important. Overall, there is little data on the manifold effects of living in space, and this makes attempts toward mitigating the risks during a lengthy space habitation difficult. Testbeds such as the ISS are currently being utilized to research some of these risks.

The environment of space is still largely unknown, and there will likely be as-yet-unknown hazards. Meanwhile, future technologies such as artificial gravity and more complex bioregenerative life support systems may someday be capable of mitigating some risks.

Timing is everything, to our genes

LA JOLLA—To everything there is a season. This saying applies to many human endeavors, but new research shows it’s even true on the molecular level. A Salk Institute study published in the journal Science on February 8, 2018, found that the activity of nearly 80 percent of genes follows a day/night rhythm in many tissue types and brain regions.

While scientists have long known that many tissues follow these cycles, called circadian rhythms, this is the most comprehensive study connecting timing to gene transcription (the process of copying DNA into RNA to guide protein assembly).

The research team pictured in front of the chronobiology facility established by Howard Cooper, at the Institute of Primate Research in Nairobi, Kenya.

Click here for a high-resolution image.

Credit: Institute of Primate Research

“This is the first time a reference map of daily gene expression has been established,” says Satchidananda Panda, a professor in Salk’s Regulatory Biology Laboratory and senior author on the paper. “It’s a framework to understand how circadian disruption causes diseases of the brain and body, such as depression, Crohn’s disease, IBD, heart disease or cancer. This will have huge impact on understanding the mechanisms or optimizing cures for at least 150 diseases.”

Using RNA sequencing, the research team tracked gene expression in dozens of different non-human primate tissues every 2 hours for 24 hours. The team found that each tissue contained genes that were expressed at different levels based on the time of day. However, the number of these “rhythmic” genes varied by tissue type, from around 200 in pineal, mesenteric lymph nodes, bone marrow and other tissues to more than 3,000 in prefrontal cortex, thyroid, gluteal muscle and others. In addition, genes that were expressed most often tended to show more rhythmicity, or variability by time.

Of the 25,000 genes in the primate genome, nearly 11,000 were expressed in all tissues. Of those (which mostly govern routine cellular functions, such as DNA repair and energy metabolism), 96.6 percent were particularly rhythmic in at least one tissue, varying drastically by when they were sampled.

In most of the tissues, gene transcription peaked in the early morning and late afternoon and quieted in the evening after dinner, around bedtime. With 81.7 percent of protein-coding genes experiencing a rhythmic effect, this timing mechanism is far more widespread than previously suspected.

“These findings provide new insights that could influence how scientific research is validated. For example, scientists trying to replicate previous work may pay closer attention to when specific assays were conducted,” says the paper’s co–senior author Howard Cooper, who is a visiting scientist at the Salk Institute. Aside from informing new research methods, this molecular timing mechanism could also impact drug effectiveness. In the future, pharmacists may provide patients more detailed instructions on how often and when to take drugs.

“We show that more than 80 percent of FDA-approved drug targets are rhythmic in at least one tissue,” says Ludovic Mure, a Salk staff scientist and first author on the paper. “In addition to the drug target, many other mechanisms that affect drug efficiency or toxicity, like its absorption, metabolization and excretion, may be modulated by the circadian clock.”

The Salk team’s gene expression atlas could also help scientists illuminate how late-night lifestyles impact human health. This could apply to shift workers or anyone who deviates regularly from the day/night cycle. In addition, this work might also advance aging studies, as these rhythms often become disrupted as people grow older.

“This is a list of how genes are differentially expressed in different organs, and that will give us a framework to understand if shift work and other disruptions change how genes are expressed,” said Panda. “For earlier circadian rhythm research, we did not have a reference, so this is like having a human reference genome.”

Other authors on the paper were Hiep Le, Giorgia Benegiamo, Max Chang and Luis Rios of Salk Ngalli Jillani, Ngotha Maini and Thomas Kariuki of the National Museums of Kenya and Ouria Dkhissi-Benyahha of the University of Lyon and INSERM.

The work was supported by a Salk Institute innovation grant, the Department of Defense, the Chapman Foundation and the Helmsley Charitable Trust, the Glenn Center for Aging Research, and the Fyssen and Catharina Foundations.

The Upcoming Solar Eclipse May Do 5 Of These Weird Things To Your Body

On Aug. 21, the moon will pass between the Earth and sun to create an incredibly magical total solar eclipse. Millions of people are preparing to witness the rare occasion, as the last one happened nearly a decade ago. As visually appealing and interesting as this eclipse promises to be, you might be wondering how the solar eclipse affects your body.

There are many ancient legends about the effects of a total solar eclipse on the human body. While not everything is backed up by science, it's always interesting to learn about people's beliefs regarding the intense power of the solar eclipse.

In astrology, the light of the sun represents life and energy. The sun is most closely associated with the self, personality, and ego, and what it is that makes you unique. It's also been said to foster creative ability and provide people with the power to meet the challenges of everyday life.

So, even though you may not think about the sun as much more than that really hot burning ball in the sky that leaves you with wicked sunburns every summer, it's worth knowing what you can expect when a solar eclipse is about to take place.

In the name of not being in the dark, here are five weird things the upcoming solar eclipse might do to your body.

1. You Might Feel Lethargic Or Tired

According to spiritual research, the total eclipse of the sun can cause feelings of tiredness or sickness.

It's also not advised to make big decisions during this time period because of the impact it can have on your mood.

2. Pregnancy Is Said To Be Affected

Pregnant women are sometimes asked to take certain precautions when it comes to a total solar eclipse, as there is a myth that claims children can be born with abnormalities during this time.

Please keep in mind there's no scientific evidence that this is true, but still, it's a wildly interesting theory.

3. You Might Suffer Eye Injuries

This one is actually backed by science 100 percent, so listen up, guys. Though you're totally going to want to look up at this amazing sight, it is extremely dangerous to look at the sun with the naked eye. Doing so can cause permanent damage to the retina, and in the worst case scenario, it can even cause blindness.

This is why special solar eclipse glasses are sold exclusively for this event.

The only time you should remove these glasses is during those two minutes or less when the sun is completely obstructed.

Oh, and don't make the mistake of thinking your favorite pair of RayBans will cut it. Suck it up and wear the special glasses, friends.

4. Your Digestion Might Be Disrupted

This is why extremely spiritual people choose to avoid meals and practice fasting during a total solar eclipse.

5. Your Emotions Might Be Out Of Whack

Many people believe that the rare occurrence of a solar eclipse has psychological effects on humans.

There are reports of increased agitation, unusual dreams, sudden bursts of creativity, and even relationship difficulties during a solar eclipse.

So, whether you find yourself painting the next Starry Night, or you simply want to hit up your nearest library for some dope eclipse shades, one thing is certain: This infrequent, literally astronomical opportunity will be a sight to see.

How Can a Trypanosome Alter Your Circadian Rhythm?

Sleeping sickness causes a variety of effects, but its effects on circadian rhythm are some of the most destructive and most interesting. As the disease progresses, people begin to sleep during the days and suffer from insomnia at night. This occurs after the parasite has infected brain tissues. The parasite attacks parts of the brain responsible for maintaining temperature and setting internal clocks. The result is that people begin to sleep and wake at odd times. Their entire internal rhythm changes, including their core body temperature. This, in turn, reinforces the parasite’s circadian clocks.

It appears that our circadian rhythms can be influenced by a variety of factors, from sunlight to metabolic oscillations to even a tiny but destructive parasite. While most readers will never have to worry about catching this illness, this research presents new options for treating sleeping sickness using chronopharmacology. Hundreds of thousands of people may soon be able to sleep more soundly.

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