On evolution statistics

This basic evolution theory question has been haunting me since childhood and I'm kind of embarrassed that I can't explain it yet:

Consider a butterfly. It's wings have evolved to look like the eyes of an owl, so to prevent it's predators who are themselves preys of the owl to attack it.

From what I've learned (and feel free to indulge me in the very basics if I get this wrong), natural selection suggests that the butterflies that didn't have the owl's eyes in their wings would be eaten, leaving the ones with the eyes to survive, right?

But that implies that this useful trait appeared in the butterfly's wings by chance. Now, I know trillions of butterflies have been born before this, but trying to figure out the possibility of this to happen by chance doesn't look like it's plausible. Let's go through the things that have to work right before this trait is passed over:

  1. For a butterfly to be born in a different wing colour, it should be a genetic mutation which doesn't happen this often, for what I know.

  2. The wings are composed of micro-scales. For every scale to compose an image so similar that confuses even us, the margin of error is very slim. It could be anything. It could be a picture of Tom Selleck for all we know. The scales must be in the correct spectrum of colour by a small margin of error. So that is already a very unlikely thing to happen.

  3. Then, this butterfly cannot be eaten out of bad luck (mind you, the wings don't guarantee it will not be eaten, just enlarge her chances).

  4. It has to mate, which also is not a guarantee to happen, since nature deals with competition. If this butterfly we are considering is a male, the female must find the wings hot, instead of being afraid of those creepy eyes.

  5. The genes of this mutations must also be dominant, so when it mates and generates offspring, at least part of the new butterflies inherit this trait.

And this is a simple example. There are animals that evolved so smartly I can't even start to think of the possibilities.

My question is, more precisely, how likely is it for a species to evolve into complex solutions?

Remi.b's answer is great, but here's something less technical if that's what you're looking for:

  1. Genetic mutations happen ALL THE TIME. Every time a cell divides, there is an error rate of about one per billion. That's a very low error rate per division, but when you multiply it by the number of divisions, times the number of cells, times the number of individuals, times the number of years the species has existed… well, that's a lot of mutations. Mind you, way fewer mutations will get passed along to offspring, because the vast majority of mutations are non-advantageous (because there a lot more ways to make a bad butterfly than a good one). But that's the job of selection, not mutation.

  2. Evolution is a step-by-step process. There doesn't just have to be mutation and advantage, there has to be an advantage every step of the way. If big circles were selected for, that means intermediate forms (smaller circles, perhaps?) were selected for too. A blob that sort of looks like Tom Selleck will not confer as many fitness advantages as a blob that looks a lot like Tom Selleck (assuming the butterflies' predators hate Magnum P.I., which as far as I'm concerned is a perfectly reasonable assumption ;-)

  3. Lots of butterflies get eaten by bad luck. But it's unlikely any trait was the result of one mutation in one individual (although it does happen sometimes). There are lots of mutations happening, and if one individual doesn't pass it along, another will. Think of this: maybe 100,000,000 years ago some butterfly developed a mutation that would be ten times more effective at discouraging predators than the owl-eye circles… but then it got stepped on by a dinosaur. You'd never know it happened, and you're left eons later wondering how a way less impressive mutation happened.

  4. There's natural selection, and there's sexual selection. Maybe the females don't like the owl-eye wings so those butterflies mate half as often as their more attractive brethren. But if the resulting offspring is four times more likely to survive, that ugly butterfly just won the gene pool lottery.

  5. That's a common misconception, traits don't have to be dominant in order to be selected for. Think of this: lactose intolerance is dominant, but in many populations lactose intolerant people are in the minority, because after the domestication of the cow being lactose intolerant was enough of a disadvantage to make those people less likely to have offspring.

One of the concepts people most often lack when dealing with evolution is of scale. You're looking at a tiny, tiny, tiny fraction of all the mutations that could have possibly happened and thinking, "What are the odds that that happened, it seems so improbable!" But that's because you're not seeing the trillions and trillions and trillions of mutations that could have happened if random chance had taken things in an ever so slightly different direction. SOMETHING had to happen, it's the laws of physics. You're only able to see and be amazed by what did happen… well, because it's the thing that ended up happening. The more you think about it, the easier it is to wrap your mind around.

In your 5 points you basically cover several concepts of evolutionary biology.

1) The number of mutations depend on mutation rate. The mutation rate varies along genome sequences, species and individuals. According to the recent DECODE study (Kong et al., 2012) a human mother transmit on average 15 mutations to her offspring and a human father transmit on average $25 + 2(g-20)$ mutations to his offsprings, where $g$ is the age of the father and where the formula stands only for father older than 20 years old.

2) Mutations happen by chance and are not directed toward creating some specific feature. But it is much more likely to create a round of color on the wings of a butterfly than creating the picture of Tom Sellek. The reason has to do with the developmental and biochemical pathways linking the given mutation to its phenotypic effect. Looking at a given mutation, you can understand how it yield to the modification of some phenotypic trait by looking at the biochemical and devlopmental pathways.

3,4) The third point that you raise is called "genetic drift". Shortly speaking the concept of genetic drift may be called the good luck/bad luck effects. Stating differently genetic drift is the random sampling of alleles (gene variant) from a population. If some alleles are favored over some others at a given locus, then sampling is not 100% random but is not either 100% deterministic. The only case where genetic drift is absent is in infinite population (which is obviously an unrealistic case). Genetic drift is inversely propotional to population size and you'll understand it better by reading this post.

5) When the mutation is at very low frequency, the mutation needs to be dominant in order to be expressed, this is true. But an allele may increase in frequency due to genetic drift up to the point that some individuals are homozygous for this allele and therefore express the trait. Dominance and recessivity are just extreme case of a continuum and most often alleles have intermediate level of dominance. Pleiotropy is also something to consider. Note also thaat the frequency of the three possible genotypes $AA$, $AB$ and $BB$ are given by Hardy-Weinberg law (under some assumptions) $x^2$, $2x(1-x)$ and $(1-x)^2$ respectively, where $x$ is the frequency of the allele $A$.

Hope that helps!

Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait.

There are many ways to use statistics and probability to see evolution in action.

Distribution of Traits

The easiest way to visualize traits within a population is to plot the frequency of each trait compared to all traits. What we find when we do this is that most traits fall into a normal distribution, as seen below:

Statistically, we can break traits into two categories: discrete and continuous traits. Discrete traits, such as hair color, can be categorized into discrete categories, like the graph on the lower right of the image above. While individual organisms fall into discrete categories, the overall distribution of the variation remains the same. Continuous traits, such as height, do not clearly fall into different categories, and each individual can be added to a continuous distribution, such as the graph on the upper right of the image.

Further, we can estimate the variation present within a population by looking and the width – or breadth – of the normal distribution. The green line represents a population with very little variability, whereas the orange line represents a trait with a much higher level of variation spread more evenly across all versions of the trait.

Trait Distribution over Time

To really see evolution in action, we have to look at the distribution of traits over time. Essentially, this is a mathematical proof that populations evolve over time – as seen in the graphs below:

Directional selection happens when the mean value for the trait shifts one direction or another. This could mean the population is getting taller, heavier, or is moving toward one end of the color spectrum. A good example of directional selection is the evolution of flippers in whales and dolphins.

Stabilizing selection happens when there are selective pressures on the extreme variations of a trait. It can be thought of as “Goldilocks selection” in that it selects for the trait that is “just right” – not too hot or too cold. An example of stabilizing selection could be the color of a population of mice. If white mice and black mice get predated at higher rates, gray mice might be selected for because they have the best camouflage.

Disruptive selection happens when a new selective pressure targets the mean trait in a population. For example, if a new predator in an environment eats only gray mice, black mice and white mice will both increase in abundance. Disruptive selection, brought on by a wide variety of selective forces on a large number of traits, can ultimately lead to a speciation event – when the population splits based on a disrupted trait it can stop interbreeding and form new species.

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5 facts about evolution and religion

Are faith and belief in evolution necessarily at odds? According to Pope Francis, the answer is no. Indeed, the pope recently reaffirmed the Roman Catholic Church’s view that “evolution in nature is not inconsistent” with church teaching on creation, pushing the debate on human origins back into the news.

Although most U.S. Catholics accept the idea of evolution in some form, a substantial percentage of American adults reject the scientific explanation for the origins of human life, and a number of religious groups in the U.S. maintain that Charles Darwin’s theory of evolution through natural selection is not correct because it conflicts with their views of creation.

Here are five facts about evolution and faith:

1 The Roman Catholic Church has long accepted – or at least not objected to – evolutionary theory. Pope Francis is not the first pontiff to publicly affirm that evolution is compatible with church teachings. In 1950, in the encyclical “Humani Generis,” Pope Pius XII said that Catholic teachings on creation could coexist with evolutionary theory. Pope John Paul II went a bit further in 1996, calling evolution “more than a hypothesis.”

2 A minority of Americans fully accept the scientific explanation for the origins of human life. According to a 2013 Pew Research Center survey, 60% of Americans say humans have evolved over time, but only about half of that group (32% of U.S. adults overall) believes that humans and other living things evolved solely due to natural processes, the explanation accepted by the vast majority of scientists. About a quarter of U.S. adults (24%) say that humans and other life evolved, but that this evolution was guided by a supreme being. The same survey found that a third of Americans (33%) reject evolution entirely, saying humans and other living things have existed in their present form since the beginning of time.

3 Of all the major religious groups in the U.S., white evangelical Protestants are the most likely to reject evolution. Nearly two-thirds (64%) of white evangelicals say that humans and other living things have always existed in their present form, while roughly one-in-ten white evangelicals (8%) say that humans evolved through natural processes. On the other end of the spectrum are the unaffiliated, a majority of whom (57%) said they believe that life evolved through natural processes.

The rejection of evolution by most evangelicals is largely mirrored by their churches, such as the Southern Baptist Convention and the Lutheran Church-Missouri Synod, which explicitly reject evolutionary theory as being in conflict with what they see as biblical truth.

On evolution statistics - Biology

Nonetheless, some writers, principally of the "creationist" and "intelligent design" schools, are not content with these grand revelations, and argue instead for a worldview that is often at odds with modern science. Old-earth geology and biological evolution are key targets of their objections, although for mostly historical reasons rather than for any fundamental issue. After all, there is no comparable opposition movement to quantum physics, organic chemistry, cetacean biology or any of a host of other scientific theories.

Both traditional creationists and intelligent design writers have invoked probability arguments in their criticisms of evolution. They argue that certain features of biology are so fantastically improbable that they could never have been produced by a purely natural, "random" process, even assuming the billions of years of history of geologic history. They further maintain that this line of reasoning can be seen by simple "back of the envelope" probability calculations. For example, they often equate the hypothesis of evolution to the absurd suggestion that monkeys randomly typing at a typewriter could compose a selection from the works of Shakespeare, or that an explosion in an aerospace equipment yard could produce a working airliner [Dembski1998 Foster1991 Hoyle1981 Lennox2009]. More recent studies of this genre argue that functional biology operates on an exceedingly small subset of the space of all possible DNA sequences, and that any changes to the "computer program" of biology are, like changes to human computer programs, almost certain to make the organism non-functional [Axe2017 Marks2017].

One creationist-intelligent design argument addresses the human alpha-globin molecule, a component of hemoglobin that performs a key oxygen transfer function. Alpha-globin is a protein chain based on a sequence of 141 amino acids there are 20 different amino acids common in living systems, so the number of potential chains of length 141 is 20 141 , which is roughly 10 183 (i.e., a one followed by 183 zeroes). These writers argue that this figure is so enormous that even after billions of years of random molecular trials, no human alpha-globin protein molecule would ever appear "at random," and thus the hypothesis that human alpha-globin arose by a "random" evolutionary process is, in their thinking, decisively refuted [Foster1991, pg. 79-83 Hoyle1981, pg. 1-20 Lennox2009, pg. 163-173].

The treacherous world of probability and statistics

To illustrate the difficulties with probability arguments, mathematics teachers often ask their class (let's say it has 30 students) if they think it is likely that two or more persons in the class have exactly the same birthday. Most students say that it is highly unlikely, thinking that the chances that two people have the same particular birthday is 1/365, and so 30 times this amount is only 30/365. But this argument is fallacious, since, for example, in a class of 30 students there are 435 pairs of students. When the probability calculation is done correctly for the case of 30 students [it is equal to 1 - (364/365 x 363/365 x . x 336/365)], one obtains 70.6%. In general, if there are 23 or more students in the class, then the chances that two or more have the same birthday is greater than 50%. For numerous other examples of how seemingly improbable "coincidences" can happen, see [Hand2014].

A similar probability fallacy is seen the alpha-globin argument, mentioned above. This argument ignores the fact that a large class of alpha-globin molecules can perform the essential oxygen transfer function, so that the computation of the probability of a single instance is misleadingly remote. Indeed, most of the 141 amino acids in alpha-globin can be changed without altering the key oxygen transfer function, as can be seen by noting the great variety in alpha-globin molecules across the animal kingdom (see DNA). When one revises the calculation above, based on only 25 locations essential for the oxygen transport function (which is a generous over-estimate), one obtains 10 33 fundamentally different chains, a enormous figure but incomparably smaller than 10 183 . A calculation such as this can be refined further, taking into account other features of alpha-globin and its related biochemistry. But do the details of these calculations really matter? Let us examine this question in detail.

The fundamental fallacy of creationist probability arguments

As this chart indicates, the key initial step in the chain of applied mathematical reasoning is to formulate an accurate mathematical model of the physical or biological phenomenon in question. If this model is not carefully constructed, then the chain of inference is broken, and it matters not in the least how good or how bad are the remaining steps.

The alpha-globin example above, along with virtually all other such arguments in the creationist-intelligent design literature, suffers from exactly this problem: The argument presumes, as its fundamental mathematical model, that the human alpha-globin arose by a single all-at-once random shot event. But generating the alpha-globin molecule "at random" in a single shot is decidedly not the scientific hypothesis in question. (This "straw man" notion, by the way, is the creationist theory, not the scientific theory, of its origin.) Instead, available evidence from hundreds of published studies on the topic has demonstrated that alpha-globin arose as the end product of a long sequence of intermediate steps, each of which was biologically useful in an earlier context. See, for example, the survey article [Hardison2001], which cites 144 papers on the topic of hemoglobin evolution many more have been published since this survey.

With regards to hemoglobin, it has long been noted that heme, the key oxygen-carrying component of hemoglobin, is remarkably similar to chlorophyll, the molecule behind photosynthesis. The principal difference is that heme has a central iron atom, whereas chlorophyll has a central magnesium atom otherwise they are virtually identical. This similarity can hardly be a coincidence, and in fact researchers concluded long ago, based on several lines of evidence, that these two biomolecules must have shared a common lineage (meaning, of course, that organisms which incorporate these biomolecules must have shared a common lineage) [Hendry1980]. Here is a diagram of the two molecules [from]:

In summary, it does not matter how good or how bad the mathematics used in the analysis of alpha-globin, given that the underlying probability model (an all-at-once random shot) is a fundamentally invalid description of the phenomenon in question. Any simplistic probability calculation of evolution that does not take into account the step-by-step process by which the structure came to be is deeply fallacious and can easily mislead [Musgrave1998 Rosenhouse2018].

Is evolution a "random" process?

What's more, such calculations completely ignore the atomic-level biochemical processes involved, which often exhibit strong affinities for certain types of highly ordered structures. For example, molecular self-assembly occurs in DNA molecule duplication every time a cell divides. If we were to compute the chances of the formation of a human DNA molecule during meiosis, using a simple-minded probability calculation similar to that mentioned above, the result would be something on the order of one in 10 1,000,000,000 , which is far, far beyond the possibility of "random" assemblage. Yet this process occurs many times every day in the human body and in every other plant and animal species. In short, extreme probabilities by themselves do not imply supernatural causation.


The fallacy here, once again, is presuming an all-at-once random assembly of molecules. Instead, snowflakes, like biological organisms, are formed as the product of a long series of steps acting under well-known physical laws, and the outcomes of such processes very sensitively depend on the starting conditions and numerous environmental parameters. It is thus folly to presume that one can correctly reckon the chances of a given outcome by means of superficial probability calculations that ignore the processes by which they formed.

Computer programs emulating biological evolution

The fact that the information theory arguments against evolution cannot possibly be valid can be seen by the rise of computer programs that mimic the process of biological evolution to produce novel solutions to engineering problems, in many cases superior to the best human efforts. This approach has been termed "genetic algorithms" or "evolutionary computing." As a single example, in 2017 Google researchers generated 1000 image recognition algorithms, each of which were trained using state-of-the-art deep neural networks to recognize a selected set of images. They then used an array of 250 computers, each running two algorithms, to identify an image. Only the algorithm that scored higher proceeded to the next iteration, where it was changed somewhat, mimicking mutations in natural evolution. Google researchers found that their scheme could achieve accuracies as high as 94.6% [Gershgorn2017]. In another Google-funded research project, a computer was programmed with only the rules of Go, together with an evolution-style "deep learning" algorithm, and then had the program play games against itself. Within a few days it had advanced to the point that it defeated an earlier Google program 100 games to zero. This earlier program, in turn, had previously defeated the world's champion human Go player [Greenmeier2017].

Improbable structures and features in nature

  1. Lenski's 2012 E. coli experiment: In January 2012, a research team led by Richard Lenski at Michigan State University demonstrated that colonies of viruses can evolve a new trait in as little as 15 days. The researchers studied a virus, known as "lambda," which infects only the bacterium E. coli. They engineered a strain of E. coli that had almost none of the molecules that this virus normally attaches to, then released them into the virus colony. In 24 of 96 separate experimental lines, the viruses evolved a strain that enabled them to attach to E. coli, using a new molecule that they had never before been observed to utilize. All of the successful runs utilized essentially the same set of four distinct mutations. Justin Meyer, a member of the research team, noted that the chances of all four mutations arising "at random" in a given experimental line (based on a probability calculation) are roughly one in 10 27 (one thousand trillion trillion) [Zimmer2012]. Note also that the chances for this to happen in 24 out of 96 experimental lines are roughly one in 10 626 .

Dembski's information theory arguments

Does creationism provide a reasonable alternative?

Here it is instructive to consider transposons or "jumping genes," namely sections of DNA that have been "copied" from one part of an organism's genome and "pasted" seemingly at random in other locations. The human genome, for example, has over four million individual transposons in over 800 families [Mills2007]. In most cases transposons do no harm, because they "land" in an unused section of DNA, but because they are inherited they serve as excellent markers for genetic studies. Indeed, transposons have been used to classify a large number of vertebrate species into a family tree, with a result that is virtually identical to what biologists had earlier reckoned based only physical features and biological functions [Rogers2011, pg. 25-31, 86-92]. As just one example, consider the following table, where columns labeled ABCDE denote five blocks of transposons, and x and o denote that the block is present or absent in the genome [Rogers2011, pg. 89].

It is clear from these data that our closest primate relatives are chimpanzees and bonobos. As another example, here is a classification of four cetaceans (ocean mammals) based on transposon data [Rogers2011, pg. 27]:

Other examples could be listed, encompassing an even broader range of species [Rogers2011, pg. 25-31, 86-92].

Needless to say, these data, which all but scream "descent from common ancestors," are highly problematic for creationists and others who hold that the individual species were separately created without common biological ancestry. Transposons typically are several thousand DNA base pair letters long, but, since there are often some disagreements from species to species, let us be very conservative and say only 1000 base pair letters long. Then for two species to share even one transposon starting at the same spot, presumably only due to random mutations since creation, the probability (according to the creationist hypothesis) is one in 4 1000 or roughly one in 10 600 . For 16 such common transposons, the chances are one in 4 16000 or roughly one in 10 9600 . What's more, as mentioned above, an individual species typically has at least several hundred thousand such transposons. Including even part of these in the reckoning would hugely multiply these odds.

But this is not all, because we have not yet considered the fact that in each diagram above, or in other tables of real biological transposon data, there is a clear hierarchical relationship. This is by no means assured, and in fact is quite improbable -- for almost all tables of "random" data, there is no hierarchical pattern, and no way to the rearrange the rows to be in a hierarchical pattern. For example, in a computer run programmed by the present author, each column of the above cetacean table was pseudorandomly shuffled (thus maintaining the same number of x and o in each column), and the program checked whether the rows of the resulting table could be rearranged to be in a hierarchical order. There were no successes in 10,000,000 trials. As a second experiment, a 4 x 16 table of pseudorandom data (with a 50-50 chance of x or o) was generated, and then the program attempted to rearrange the rows to be in a hierarchical pattern as before. There were only three successes in 10,000,000 trials.

Like the calculations mentioned earlier, these calculations are simplified and informal more careful reckonings can be done, and one can vary the underlying assumptions. But, again, do the fine details of the calculations really matter? One way or the other, it is clear that the creationist hypothesis of separate creation does not resolve any probability paradoxes instead it enormously magnifies them.

The only other possibility, from a strict creationist worldview, is to posit that a supreme being separately created species with hundreds of thousands of transposons already in place, essentially just as we see them today. But this merely replaces a scientific disaster (the utter failure of the creationist model to explain the vast phylogenetic patterns in intron data) with a theological disaster (why did a truth-loving supreme being fill the genomes of the entire biological kingdom with vast amounts of misleading DNA evidence, all pointing unambiguously to an evolutionary descent from common ancestors over the eons?). Indeed, with regards to the discomfort some have about evolution, the creationist alternative of separate creation is arguably far worse, both scientifically and theologically. See Deceiver for additional discussion.


  1. Many of these arguments presume a mathematical model where the structure in question came into existence "at random" via a single-shot chance assemblage of atoms. But this is not the scientific hypothesis of how they formed (they were the result of a long series of intermediate steps over the eons). Thus all such "straw man" arguments are fatally flawed from the beginning.
  2. Some of these arguments rely on sophisticated mathematical calculations, but given that the underlying probability model is an invalid description of the phenomenon in question, it does not matter in the slightest how good or how bad these reckonings are.
  3. Many of these arguments apply faulty reasoning, such as by ignoring the fact that a very wide range of biomolecules could perform a similar function to the given biomolecule. Thus the odds they provide against the formation of the given biomolecule are often greatly exaggerated.
  4. These arguments typically ignore the fact that biological evolution is fundamentally not a purely "random" process -- mutations may be random, but natural selection is far from random.
  5. These arguments typically ignore reams of evidence from the natural world that evolution can and often does produce highly improbable structures and features.
  6. Some writers attempt to invoke advanced mathematical concepts (e.g., information theory), but derive highly questionable results and misapply these results in ways that render the conclusions invalid in an evolutionary biology context.
  7. The creationist hypothesis of separate creation for each species does not resolve any probability paradoxes instead it enormously magnifies them.

Perhaps at some time in the distant future, a super-powerful computer will be able simulate with convincing fidelity the multi-billion-year biological history of the Earth, in the same way that scientists today attempt to simulate (in a much more modest scope) the Earth's weather and climate. Then, after thousands of such simulations have been performed, researchers might obtain some meaningful statistics on the chances involved in the origin of life, or in the formation of some class of biological structures such as hemoglobin. Perhaps also researchers will eventually reconstruct, in the laboratory, additional key steps in the formation of the most primitive biomolecular structures involved in the origin of life. Perhaps one day researchers will even discover forms of life on other planets.

Until that time, the probability and information theory calculations that appear in creationist-intelligent design literature and elsewhere should be viewed with great skepticism, to say the least. As mathematician Jason Rosenhouse writes [Rosenhouse2018],

When biologists ascribe to evolution the ability to craft information-rich genomes, they are neither speculating nor guessing. The basic components of evolutionary theory are empirical facts. Genes really do mutate, sometimes leading to new functionalities. The process of gene duplication with subsequent divergence leads to the creation of information by any reasonable definition of the terms. Selection can string small variations together into directional change. On a small scale, this has all been observed. And if small increases in information are an empirical reality on human timescales, then what abstract principle of mathematics is going to rule out much larger increases on geological scales?

Then here come the ID [intelligent design] folks, full of swagger and bravado. They say the accumulated empirical evidence must yield before their back-of-the-envelope probability calculations and abstract mathematical modeling. Evolution should be abandoned in favor of the new theory of intelligent design. This theory states, in its entirety, that an intelligent agent of unspecified motives and abilities did something at some point in natural history. Not very useful.

In a larger context, one has to question whether highly technical issues such as molecular structures or calculations of probabilities have any place in a discussion of philosophy or religion. For example, one can search in vain for even a single passage in the Bible or other similar texts that is written in the highly rigorous, quantitative style of a scientific paper. So why attempt to "prove" a point with probability arguments, especially when there are very serious questions as to whether such reasoning is valid? One is reminded of a passage in the New Testament: "For if the trumpet gives an uncertain sound, who shall prepare himself for the battle?" [1 Cor. 14:8]. It makes far more sense to leave such matters to peer-reviewed scientific research.

For Darwin Day, 6 facts about the evolution debate

Photograph of Charles Darwin by Maull and Polyblank for the Literary and Scientific Portrait Club (1855) via Wikimedia Commons.

Tuesday is the 210th anniversary of Charles Darwin’s birth, a day now celebrated by some as Darwin Day. Darwin is best known for his theory of evolution through natural selection. When Darwin’s work was first made public in 1859, it shocked Britain’s religious establishment. And while today it is accepted by virtually all scientists, evolutionary theory still is rejected by many Americans, often because it conflicts with their religious beliefs about divine creation.

While not an official holiday, Darwin Day has been adopted by scientific and humanist groups to promote everything from scientific literacy to secularism. This year, dozens of events have been planned worldwide, many of them anchored by scientific talks or symposiums.

To mark the occasion, here are six facts about the public’s views on evolution, as well as other aspects of the debate in the U.S. and elsewhere:

1 Roughly eight-in-ten U.S. adults (81%) say humans have evolved over time, according to data from a new Pew Research Center study. This includes one-third of all Americans (33%) who say that humans evolved due to processes like natural selection with no involvement by God or a higher power, along with 48% who believe human evolution occurred through processes guided or allowed by God or a higher power. The same survey found that 18% of Americans reject evolution entirely, saying humans have always existed in their present form. (See the full report for a deeper look at the ways question wording and format can affect survey results on evolution.)

2 Around four-in-ten white evangelical Protestants (38%) say humans have always existed in their present form, and about a quarter (27%) of black Protestants share this view, according to the new study. Among white mainline Protestants, just 16% say humans have always existed in their present form. Similar shares of Catholics (13%) and the religiously unaffiliated (11%) say the same. Only among the religiously unaffiliated – those who describe their religion as atheist, agnostic or “nothing in particular” – do a majority (64%) accept evolution via natural selection with no involvement from God or a higher power. Both Protestants and Catholics are considerably more likely to say evolution was guided or allowed by God than they are to say that humans evolved due to processes such as natural selection, or to say that humans have always existed in their present form.

3 Scientists overwhelmingly agree that humans evolved over time, and most Americans are aware that this is the case. Among scientists connected to the American Association for the Advancement of Science, 98% say they believe humans evolved over time. Roughly three-quarters (76%) of Americans perceive that most biological scientists hold this view, according to the new study. Those in the general public who reject evolution are divided on whether there is a scientific consensus on the topic: 46% say most biological scientists think humans have evolved due to processes such as natural selection, and 52% say most biological scientists think humans have always existed in their present form.

4 A series of court decisions have prohibited the teaching of creationism or intelligent design in public schools. In spite of efforts in many American states and localities to ban the teaching of evolution in public schools – or to teach alternatives to evolution – courts in recent decades have consistently rejected public school curricula that veer away from evolutionary theory. In Edwards v. Aguillard (1987), for instance, the U.S. Supreme Court ruled that a Louisiana law requiring public school students to learn both evolution and creation science violated the Constitution’s prohibition on the establishment of religion.

5 While most Americans (59%) say science and religion are often in conflict, those who are more religiously observant are less likely than others to see this clash between faith and science, according to a 2015 Pew Research Center survey. Among those who attend church at least once a week, half (50%) view religion and science as in conflict, compared with nearly three-quarters (73%) of those who seldom or never attend worship services. At the same time, most people (68%) say that their own personal religious beliefs do not clash with accepted scientific doctrine.

6 Outside the U.S., there are many other countries where sizable shares of the population reject evolution. In Latin America, for example, roughly four-in-ten or more residents of several countries – including Ecuador, Nicaragua and the Dominican Republic – say humans and other living things have always existed in their present form. This is true even though the official teachings of Catholicism, which is the majority religion in the region, do not reject evolution. In Central and Eastern Europe, evolution is broadly accepted, but roughly half or more of adults in two countries – Armenia and Bosnia – reject it. Meanwhile, Muslims in many nations are divided on the topic, although majorities of Muslims in countries such as Afghanistan, Indonesia and Iraq reject evolution.

It’s important to note that our international surveys have used a different approach to ask about evolution, so results are not directly comparable to our new U.S. survey (although some of our older U.S. surveys used similar questions).

Note: This is an update to a post originally published on Feb. 12, 2015.


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NOVA’s Evolution Lab Worksheets and Interactive Lessons
Explore the evidence of evolution with these worksheets based off of NOVA’s Evolution Lab. These worksheets contain questions for each level and video of the Evolution Lab and provide assessment on topics like cladograms, fossil evidence of evolution, DNA and genetics, biogeography, applications of phylogeny to health, and human evolution. The worksheets are divided into missions and are designed to be completed while playing through the game. The worksheets feature multiple choice questions, short response questions, and cladogram drawings.

The interactive lessons are digital versions of the worksheets and contain the same content from the worksheets.

The National Center for Science Education is the only national organization devoted to defending the teaching of evolution in public schools. NCSE’s Evolution Primers are written by NCSE’s scientific staff to explain key concepts or findings in evolution that are frequently misrepresented by creationists. NCSEteach is a network that brings science teachers together, allows educators to connect with one another (and NCSE staff), guides them to good-quality and well-vetted resources, shares stories of how teachers have dealt with challenges to science education and also connects them to early career scientists as a resource.

Misconception Monday
Stephanie Keep’s blog posts on the NCSE website cover common misconceptions about evolution that appear everywhere from textbooks to science news articles.

Understanding Evolution
Understanding Evolution is your one-stop shop for teaching and learning about evolution from kindergarten through college. Get friendly, clear background information as well as animations, comics, interactive investigations, news briefs, research profiles, and a database of free, vetted lessons for your classroom.

HHMI BioInteractive
The evolution collection contains short films, interactives, and classroom activities that cover mechanisms of evolution, human evolution, phylogeny, and more.

Teaching Evolution through Human Examples
This NSF-funded project from the Smithsonian contains 4 curriculum units for AP Biology classes that use human case studies to teach core evolutionary principles. The curriculum units include Adaptation to Altitude, Malaria, Evolution of Human Skin Color, What Does It Mean To Be Human, and a unit called Cultural and Religious Sensitivity.

Shape of Life
Shape of Life is a series of short classroom videos that depict evolution of the animal kingdom on Earth. Shape of Life focuses on biodiversity, adaptability, body structure, design, behaviors, and the innovative scientists who explore these creatures. Shape of Life includes videos, lesson plans, readings aligned with the Common Core, illustrations, and relevant resources.

Birds-of-Paradise Project
The birds-of-paradise are among the most beautiful creatures on earth—and an extraordinary example of evolutionary adaptation. On this site you can find what few have witnessed in the wild: the displays of color, sound, and motion that make these birds so remarkable. Then you can delve deeper, examining the principles that guided their evolution and the epic adventure it took to bring us all 39 species. There are also free lesson plans that explore the topics of the scientific process, natural and sexual selection, behavior, and heritability through hands-on activities and lively discussions:

All About Fancy Males
All About Fancy Males is an eight section online interactive developed to accompany one of the most respected introductory evolution courses in the country—Cornell University’s Evolution and Biology and Diversity. This interactive allows students and the general public to develop a solid understanding of fundamental concepts in evolution while exploring rare behavioral clips and engaging animations.

Have questions about these resources or suggestions for additional resources we should add to the collection? Let us know in the comments!

Establishing Sample Size

An important part of any biological experiment involves correctly choosing samples and selecting the right number of trials. A basic introduction to statistics provides background in statistical randomness and the law of large numbers. When conducting a study of whether insects prefer to eat American elm leaves or Princeton elm leaves, for example, using a properly randomized sample of both types of leaves helps control for confounding factors. For example, choosing a small number of leaves from the American elm, if those were all from a single tree, might result in a tree that was unusually filled with insects and would bias the results. Selecting many hundreds of leaves from a random sample of trees, however, reduces this type of error.

Evolution Is Finally Winning Out Over Creationism

Photo by J. Cameron/Wikimedia Commons.

Few issues have divided the American public as bitterly as Charles Darwin’s theory of evolution by natural selection. Since On the Origin of Species was published in 1859, it has driven a wedge between those who accept that humans and this planet’s other inhabitants have evolved over time, and those who believe that our species was created in its current form with no alterations. While the majority of people in Europe and in many other parts of the world accept evolution, the United States lags behind. Today, 4 in 10 adults in America believe that humans have existed in our present form since the beginning of time, and in many religious groups, that number is even higher. This is woeful.

Now, at long last, there seems to be hope: National polls show that creationism is beginning to falter, and Americans are finally starting to move in favor of evolution. After decades of legal battles, resistance to science education, and a deeply rooted cultural divide, evolution may be poised to win out once and for all.

The people responsible for this shift are the young. According to a recent Pew Research Center report, 73 percent of American adults younger than 30 expressed some sort of belief in evolution, a jump from 61 percent in 2009, the first year in which the question was asked. The number who believed in purely secular evolution (that is, not directed by any divine power) jumped from 40 percent to a majority of 51 percent. In other words, if you ask a younger American how humans arose, you’re likely to get an answer that has nothing to do with God.

The increase in younger people embracing evolution is “quite striking,” says Kenneth R. Miller, a biologist at Brown University and an expert witness the landmark court case Kitzmiller v. Dover, which kicked “intelligent design” out of public school classrooms in 2005. “We’re moving in the right direction.”

It’s not just the young who are moving in favor of secular evolution. The overall proportion of Americans who believe in secular evolution has doubled since 1999, from 9 percent to 19 percent, according to a 2014 Gallup poll. But it’s important to note that the jump in secular evolution does not necessarily correspond to an increase in the total number who believe in evolution. Instead, most of that increase has been drawn from the pool of Americans who previously reported that they believed in evolution guided by God, which simultaneously dropped from 40 percent to 31 percent.

Could these numbers be merely a blip—a stray mutation that will soon be weeded out of the population? Fortunately, there are several signs that these numbers do reflect a shifting cultural tide.

First, America is getting less religious. Today’s younger Americans no longer have the strong ties to organized religion that their parents did. About 56 million people now call themselves “nones” —meaning that they identify as atheist, agnostic, or nothing in particular on national surveys—a jump of 19 million since 2007, according to the 2014 Pew Research Center survey. Again, it’s the younger generation who are driving this shift: Fully 36 percent of young adults between 18 and 24 identify as nones, and the number of millennial adults who are religiously unaffiliated is growing fast.

That is not to say that religion doesn’t still exert a powerful hold on American identity it does. However, the fact that fewer people are identifying with an organized religion is good news for science education, because many of those religions have historically opposed evolution.

Who are the people still perpetuating the view that evolution is a myth and that humans have existed basically as-is for the entirety of existence, which has lasted only about 10,000 years? By and large, they’re older Americans. About 34 percent of Americans 50 to 64 years old believe in creationism. For Americans older than 65, it’s 37 percent. From the perspective of people who endorse evolution, that’s a good thing—because, not to be insensitive, but old people die. When these elderly creationists shed their mortal coil, they will be replaced by that younger generation consisting increasingly of nones. The result: a steady phasing out of those who oppose evolution.

The gay rights movement had a word for this: generational momentum. “Which is a polite word for death,” says Evan Wolfson, the president and main architect behind Freedom to Marry. “That was our secret weapon: Old people die.”

Of course, old people dying wasn’t the only reason America finally made the historic decision this year to legalize same-sex marriage, Wolfson adds. To turn that cultural tide in such a short period of time, the supporters of gay marriage had to do something far more difficult: change deeply rooted attitudes and beliefs. Similarly, for the movement behind evolution to triumph, younger Americans who have been raised to believe in creationism need to be open to changing their minds. Fortunately, today’s generation is growing up in a time of greater open-mindedness and willingness to listen to evidence-based thinking, Wolfson says. Rather than being blinded by ideology, today’s young adults are open to evidence, facts, and reason. They want “information, not ideology.”

“Young people are growing up with a less ideological closed mind,” Wolfson told me. “Which is what a lot of the anti-evolution, anti–climate evolution, anti–climate change thinking is: It’s an ideology. It’s a refusal to engage with reality. Hopefully what we’re seeing here is that younger people are less prone to that. They’re allowing themselves to see the reality in front of them, as opposed to shutting their eyes on the basis of ideological denial. … They’re growing up in the midst of the conversation, growing up in the midst of reality, being open to reality, and not simply refusing to see what’s in front of you.”

There are many reasons for this shift. One is improving science education (more on that later). But another is that, in some ways, they don’t have a choice, argues Daniel Dennett, co-director of the Center for Cognitive Studies at Tufts University and co-author of Caught in the Pulpit: Leaving Belief Behind. He credits the rise of the Internet and the fact that today’s young people are more interconnected than ever before. “What is particularly corrosive to religion isn’t just the newly available information that can be unearthed by the curious,” Dennett wrote in April, in an op-ed entitled “Why the Future of Religion is Bleak” in the Wall Street Journal, “but the ambient knowledge that is shared by the general populace.”

For many Americans, evolution is in the cultural air we breathe. This year’s blockbuster Jurassic World takes as its premise the idea that birds evolved from dinosaurs. Or consider the television show The Big Bang Theory—which elevates science, including evolution, far above religion. In one memorable episode, Sheldon, a string theorist, flees back to his home and his religious mother in Texas after reaching a low point in his career. “This is my home now,” Sheldon tell his friends, who have followed him in an attempt to convince him to return. “Thanks to you, my career is over, and I’ll spend the rest of my life here in Texas—trying to teach evolution to creationists.”

His mother comes into the room. “You watch your mouth, Shelly,” she snaps. “Everyone’s entitled to their opinion.”

Sheldon: “Evolution isn’t an opinion, it’s fact.”

Mother: “And that is your opinion.”

Sheldon’s mother is laughed out of the room.

The message is clear: The fact-ness of evolution, at least to viewers of the show, is indisputable, and creationism is little more than a joke. Realizing the kind of nonsense he will have to deal with if he stays, Sheldon decides to return to his scientific career.

Of course, evolution hasn’t won yet—not even close. Even today, plenty of powerful people are still promoting creationist nonsense, notably Louisiana Gov. Bobby Jindal, as Miller and Zack Kopplin have pointed out in Slate. Moreover, we can’t forget that a large bloc of young-Earth creationists still isn’t budging. Remember that 4 in 10 number? For those who attend church or synagogue at least weekly, that number is closer to 50 percent. For white evangelicals, it’s 60 percent. Those percentages haven’t budged in more than 30 years.

One of the greatest challenges to science literacy is the patchwork nature of the American educational system, says Josh Rosenau, programs and policy director at the National Center for Science Education. Despite the fact that the case law has been on the side of evolution and against creationism for decades, it’s impossible to know exactly what is going on inside the individual classroom. “That’s what makes our work so hard and so slow,” says Rosenau. “Even if a teacher isn’t teaching creationism, that doesn’t mean she’s adequately teaching evolution.”

“The biggest problem we’ve had is teachers who self-censor,” adds Eugenie Scott, co-founder of the NCSE and a former science teacher who has been part of the evolution versus creationism debate for more than two decades. “They’re responding to this very pervasive ‘There’s something wrong with evolution’ mentality. There are too many teachers around the country who anticipate that they’re going to get pushback if they teach the e-word, so they skip that section of the textbook. ‘Sorry kids, we don’t have time to cover everything—let’s go on to photosynthesis.’ ”

Scott is optimistic, but she’s also realistic. “We won’t have won until evolution gets taught as casually as we teach photosynthesis,” she says. “And we’re a long way from that.”

Wolfson agrees. Just because the trends show evolution’s supporters have the momentum doesn’t mean we can stop fighting, teaching, or speaking out. “This isn’t just some given that will drift along on its own,” says Wolfson. “It’s something to be nurtured and defended. We didn’t win the freedom to marry only because we had the momentum we built that momentum. And we worked hard to harness it to the work of winning. The same goes for educating young people, promoting a scientific outlook and rational policy decision-making. None of it happens by itself. We still need to do the work.”

The fight matters because we’re talking about the most fundamental tenet of modern biology. Origin of Species was just voted the most influential academic book of all time. As biologist Theodosius Dobzhansky wrote in 1973: “Nothing in biology makes sense except in the light of evolution.” Shared ancestry and adaptation by natural selection are what tie the biological sciences together, give them shape and meaning, and explain why life on Earth became the way it is. Trying to teach biology without evolution would be like trying to teach chemistry without the periodic table of elements: It just doesn’t work.

Moreover, evolutionary theory doesn’t exist in a vacuum. Beyond biology, evolution is supported by and makes sense of findings in geology, paleontology, isotope chemistry, biomedicine, and other fields. If we want to be a nation of politically and scientifically literate and informed people, then we have to teach good science—and that starts with evolution. “What makes the United States a world leader is our technology,” as Bill Nye (the Science Guy) said in a 2014 public debate with creationist Ken Ham. “If we continue to eschew science … we are not going to move forward, we will not embrace natural laws, we will not make discoveries, we will not invent.”

The trends reflected in the polls are good news. Let’s hope this means that Americans will embrace evolution regardless of their political and religious beliefs—even if the process of getting there feels as gradual as evolution itself.

Evolution Vs. Creationism: Study Reveals Public School Science Lagging

The majority of public school biology teachers across the country shy away from teaching evolution, keeping instruction to a few short hours, a study has shown.

Research from two Penn State professors reveals American students may be lagging behind in their knowledge of evolution because teachers are unprepared or unwilling to teach it. Some teachers advocate creationism, while others are afraid to address the topic for fear of controversy.

The findings come at a time when reports that less than half of American students are proficient in science has focused a national spotlight on the inadequacies of science education in the nation's public schools.

In their new book, "Evolution, Creationism and the Battle to Control America's Classrooms," Michael Berkman and Eric Plutzer explore the ongoing conflict between religious and scientific teachings.

The pair analyzed data from a survey of biology teachers across the country.

The data was collected from 926 nationally representative participants in the National Survey of High School Biology Teachers, which polled them on what they taught in the classroom and how much time they spent on each subject. They also noted the teachers' personal feelings on creationism and evolution.

On the surveys, many teachers indicated that they steer clear of discussing human evolution completely, while the majority only dedicated a small amount of class time to the subject.

Seventeen percent of teachers surveyed did not cover human evolution at all in their biology class, whereas a majority of teachers (60%) spent between 1 and 5 hours of class time on it.

Many teachers among the 60 percent that kept evolution instruction brief explained that they wanted to avoid confrontation with students and parents who believe in creationism. In many cases, their own evolution knowledge was also limited.

At the opposite extreme, 13 percent of teachers explicitly endorse creationism or intelligent design, and spend at least on hour of class time presenting it in a positive light. An additional 5 percent reported that they support creationism in passing or when answering students' questions.

The remaining fraction of teachers, who Berkman and Plutzer dub the "cautious 60 percent," avoids choosing sides. Often these teachers have not taken courses in evolutionary biology and lack confidence in their ability to answer questions from skeptical or hostile students and parents.

Watch the video: Στατιστικά survivor (January 2022).