Overused Evolution: A Response

I have finally managed to cobble together a response to Jim’s two posts on overused evolution.   I don’t address all his gripes, but I thought that a few observations were in order. 

First, to casually dismiss Darwin -- as Jim does – based on a claim that his ideas aren’t new – that the notion that species have changed over time is as old as the Greeks – is like saying Niels Bohr wasn’t so great because Democritus had already developed the theory of the atom in 400 BCE.   These early evolutionary theorists may have guessed at the fact that living things changed over time, but they had no idea how.   Here’s what the 3rd century Roman writer Censorinus said about Anaximander of Miletus, the guy who came up with the early Greek theory:   

Anaximander of Miletus considered that from warmed up water and earth emerged either fish or entirely fishlike animals. Inside these animals, men took form and embryos were held prisoners until puberty; only then, after these animals burst open, could men and women come out, now able to feed themselves.

I’d say that the theory of evolution still needed some work.  

What Darwin achieved that no one had done before, except for maybe Alfred Russel Wallace, was to figure out the mechanism for the change, namely the unique variations of every individual within a species and natural selection from those variations.   He added a few other important details, like the idea that all species are descended from a common ancestor, but natural selection is the big one.  "Up until 1859," said evolutionary biologist H Ernst Mayr, "all evolutionary proposals endorsed linear evolution, a teleological march toward greater perfection."  Darwin’s thinking changed all that.  

Biologist and geneticist Theodosius Dobzhansky entitled his 1973 essay "Nothing In Biology Makes Sense Except In The Light Of Evolution."  I think that most biologists would agree.  It’s hard to overestimate Darwin’s contribution.

But, I have another, more important quibble here.  Jim should not be blaming Darwin for his own irritation over the loose talk around the water cooler about natural selection.  In my view, Jim’s problems are more with the ultra-Darwinists, also known as the adaptationists, and, in particular, the evolutionary psychologists.

Right off the bat, we must be clear that Darwin was himself not an ultra-Darwinist.  He did not believe that every human trait was an adaptation determined by natural selection.  Here’s what he wrote in the last (1872) edition of The Origin of Species ten years before his death: 

But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position—namely, at the close of the Introduction—the following words: “I am convinced that natural selection has been the main but not the exclusive means of modification.” This has been of no avail. Great is the power of steady misrepresentation; but the history of science shows that fortunately this power does not long endure. 

Unfortunately for Darwin, the power of misrepresentation is even greater than he imagined, and people – Jim for one – still labor under it.  

Let us consider the real culprits, starting with the evolutionary psychologists.  They follow the adaptationist program, but they compound the errors with their focus on behavior.  As psychologist Christopher Ryan writes:  “Anyone who takes evolutionary psychology seriously has to overcome the fact that many of the most prominent voices in the field don't.”

As I understand it, the basic tenet of evolutionary psychology is that common human behaviors have developed the same way evolutionary psychologists believe that human all physical features developed:  as the result of genetic mutations – this time within the brain – that have been honed by natural selection to serve a particular purpose.   The proposal is that these behaviors were “selected” at the dawn of human existence because they provided a reproductive advantage to our Pleistocene ancestors.  Thus, ultimately, we must understand human behavior as a mechanism to give evolutionary advantage so that our genes can be passed to the next generation.

At bottom, the problem with this view is its willingness to leap to conclusions on seriously inadequate evidence.   It is almost laughably oversimplified for many reasons, and I just touch upon a few of them here.  

First, as Darwin correctly recognized, not every attribute or feature in an organism is the result of adaptation.  For biologists, adaptation has a technical meaning:  an adaptation is a feature produced by natural selection for its current function.   Today’s biologists tend to be cautious about labeling any trait as an adaptation.  They insist that a heavy burden of proof be met before a trait can be considered adaptive.  Indeed, there are several other possibilities.   Here are a few:

1.     A trait might reflect features of an ancestor of a species that are present in the species only due to developmental constraints. The fact that the first land vertebrates (tetrapods) had four limbs wasn’t an adaptation in itself; it was a consequence of their having evolved from four-limbed fishes.  This, by the way, answers Jim’s questions about why humans didn’t “evolve wings, or poison spittle, or a taste for stationary plants (vegans a million years ago), or a better sense of smell, or high frequency speech that would stun the game.”  Evolution must work with the materials at hand and, while there is debate over whether the evolutionary change is always constant, there is no doubt that it is always incremental.  (By the way, we did develop a taste for stationary plants – see discussion of plasticity below.) 

2.     A trait may be a by-product of another characteristic.   That mammals’ blood is a red color is not an adaptation.  Mammals with red blood do not manage to survive better than mammals with yellow or blue blood.  Our blood is red because it contains iron. Natural selection had a role in placing iron in the blood, since the iron enhances its oxygen-carrying capacity.  The resultant red color of the blood is not an adaptation; it’s merely a side effect.  The late paleontologist Stephen J. Gould used an architectural term, spandrels, to help describe these genetic side effects. 

3.     A trait may be an outdated adaptation, or a vestigial structure.  A vestigial structure is a feature that was an adaptation for the organism's ancestor, but that evolved to be non-functional because the organism's environment changed.  Scientists have hypothesized that the large, hard-shelled fruit of the calabash tree was actually an adaptation for seed distribution by large mammals. Unfortunately, these mammals went extinct over 10,000 years ago.  If the hypothesis is correct, these fruit characteristics were once adaptations for seed distribution but are no longer.   Another example:  the ostrich wing once an adaptation is no longer needed for its original purpose. 

4.     A trait may be an exaptation, a feature that performs a function but that was not produced by natural selection for its current use.  Feathers originally developed to control body temperature but later proved useful in flight.  

5.   Another feature of an organism that is not be an adaption is one that resulted from genetic drift.  This is perhaps the most common source of a trait that is not an adaptation, and is also the most difficult to explain.  Darwin did not recognize genetic drift because he knew nothing of the science of genetics.  But many biologists today believe that most of the variation found in evolutionary lineages is a product of random genetic drift and not adaptation.

Genetic drift involves gene variants, called alleles.   The most well known alleles are the variants for the two genes for eye color.  One eye color gene has two variations, brown and blue, as does the other gene -- green and blue.  Normally, since the variations are random, one would expect gene variation frequencies to remain constant from one generation to the next.   If, however, a population is limited in size, then the frequency of a gene variant will not be exactly reproduced in the next generation due to an insufficient sample.

You can make an analogy to flipping a coin.  The expectation is that heads will turn up 50% of the time because there are only two sides to a coin.  For the same reason, gene variant frequencies would be expected to remain constant from one generation to another.  But, if you flip a coin just a few times, heads may or may not turn up half the time.   In other words, when a sample is very small, the likelihood that the expected outcome will not occur is high.   The more times that you flip your coin, the more likely it will approach the expected 50% heads.  The same is occurs when a population is too small:  it becomes less likely that the gene variants will remain constant.

This process of random fluctuation continues generation after generation.   There is no force pushing the frequency back to its initial state – because the population has no "genetic memory" of its state in a previous generation. Each generation is an independent event.   Often, the final result of this random change in allele frequency is that the one variant is eliminated.  So, even in the absence of selective forces, genetic drift can cause two separate populations that began with the same genetic structure to drift apart into two divergent populations with different sets of alleles.   Most of the genetic changes caused by drift do not affect fitness and so are not eliminated by natural selection.

In any event, this failure to consider other sources for features in an organism is the first problem of the evolutionary psychologist. 

The second problem is the assumption that particular human behaviors are the result of genetic makeup.  Much of human behavior is learned and does not directly reflect genetics.  Necessarily, any behavior pattern that is not uniform across all cultures cannot be due to a genetically mandated adaptation.  Similarly, any behavior pattern that is not uniform across time from the emergence of Homo sapiens cannot be an adaptation.   Rarely does evolutionary psychology have the data sufficient to establish this kind of universality. 

Along these lines, the evolutionary psychologists ignore the concept of plasticity.   Plasticity is the ability of an organism to change its physical and behavioral characteristics in response to changes in its environment.  All living things can adjust to circumstances to some extent.  A highly specialized animal or plant with little plasticity lives only in a well-defined habitat, and cannot survive if its narrow needs are not met.  Many herbivores are like this; extreme examples are koalas that depend on eucalyptus, and pandas that require bamboo. A generalist with high plasticity, on the other hand, eats a range of food, and can change its eating habits to adjust to many different conditions. Examples are humans, rats and crabs.   Plasticity itself of course is an adaptation. 

It’s hard to dispute that flexibility is one of the defining characteristics of the human species. Humans inhabit an extraordinary range of environments and exhibit an extraordinarily wide range of behavior.   We are highly responsive to novel situations – we have been able to invent means of exploring outer space and the ocean depths, environments totally alien from the conditions in which we evolved.

Some of our flexibility is biological:  when we visit higher elevations, our bodies begin to produce more red blood cells that compensates for decreased oxygen levels, eventually allowing breathing and heart rate to return to normal.  Talk to Sean about living in Bogotá.   We can also adjust to a wide range of temperature and humidity.   Talk to Pete the Elder and Lisa about living in Senegal. 

We can also adjust our physical capabilities to our environment as a matter of choice.  You can be a 97-pound weakling at the mercy of the natural elements, or with some hard work you can be a tough Charles Atlas.  Jim in his post complained about the ineluctable conversation that at some point arises at almost every party – in which people bring up the early evolutionary development of the foot and the idea of “persistence hunting.”   While I appreciate how this could get tiresome, the fact is that endurance is an area of even greater plasticity among humans.  Nobody comes out of the box with the ability to run marathons, but physical plasticity allows us to alter the expression of these genes to increase endurance considerably.

When Ellen came home from school after her very first high school swim practice she was in tears – I exaggerate not one whit.  Between sobs she begged us not to make her continue on the swimming team.  Her complaint:  “the practice was so hard!”  She said she was shocked by the level of difficulty of the workouts and didn’t see how she could possibly endure them.  Well, for some reason she remained on the team, and was soon swimming between 5 and 6 miles every day at practice.  Few organisms have this degree of plasticity and none based on the strength of will of the individual organism.  If Ellen were thrown into an environment where she had to swim five miles a day to survive, given a little time, she no doubt would manage. 

But where humans show the most plasticity is in behavior.   Today, biologists understand that, rather than selecting humans for specialized behavior traits, human evolutionary history has selected behavioral plasticity or learning capacity.   

Data from the literature on learning shows overwhelmingly the powerful influence of the environment in shaping both human behavioral similarities and differences.  As the evolutionary biologist Douglas Futuyma put it:  “On balance, the evidence for the modifiability of human behavior is so great that genetic constraints on our behavior hardly seem to exist.  The dominant factor in recent human evolution has been the evolution of behavioral flexibility, the ability to learn and transmit culture.” 

And, finally, the third problem with evolutionary psychology: we really have no idea how our Pleistocene ancestors lived.  We can imagine how they might have lived, but basing conclusions on speculations about how certain behaviors might have provided an advantage to them, is hardly scientific. 

The arguments over evolutionary psychology and ultra-Darwinism get heated because there’s plenty at stake.  If human behaviors are largely adaptations selected by nature and mandated by our genes, then we in fact live in the best of all possible worlds.  Nothing can be done – and nothing ought to be done – to alter the hidden hand of natural selection and our genetic makeup.  But, if behaviors are the result of cultural influence or our own choices, then human behavior and conditions can be improved by altering culture. And so Scrooge pleads with the spirit at the end of “A Christmas Carol”:  “Tell me that is so by what you've shown me. …  Say that I may change these things... by an altered life.”

Gould and his co-author Richard C. Lewontin called the adaptionist program “Panglossian.” Master Pangloss in Voltaire’s Candide spells out the silly logic of the best of all possible worlds, and he sounds strikingly like the evolutionary psychologists:

  

Master Pangloss taught the metaphysico-theologo-cosmolonigology. He could prove to admiration that there is no effect without a cause; and, that in this best of all possible worlds, the Baron's castle was the most magnificent of all castles, and My Lady the best of all possible baronesses.

“It is demonstrable,” said he, “that things cannot be otherwise than as they are; for as all things have been created for some end, they must necessarily be created for the best end. Observe, for instance, the nose is formed for spectacles, therefore we wear spectacles. The legs are visibly designed for stockings, accordingly we wear stockings.  Stones were made to be hewn and to construct castles, therefore My Lord has a magnificent castle; for the greatest baron in the province ought to be the best lodged.

Like Master Pangloss, the ultra-Darwinists believe that all things are created for some end, indeed, the best end, and, therefore, things cannot be other than they are.  This is the sort of thinking that might have discouraged America’s founders from embarking on an experiment in democracy.

And not only that:  if human behaviors are genetic mandates, then humans must have always lived in the best of all possible worlds – as other species live.  

But we know that the past does not represent the best of all possible worlds, because we have improved upon it.   As various commentators have noted, there is significantly less violence and poverty in the world today.   Statistics reveal dramatic reductions in war deaths, family violence, racism, rape, murder and other sorts of violence.  Steven Pinker himself writes: "The decline of violence may be the most significant and least appreciated development in the history of our species."  Beyond that, people are better educated, better fed and less persecuted than in the past.  The role and political standing of women is changing throughout the world.  Humans live significantly longer and healthier lives.   Clearly, these things just don’t happen on their own.  Human action one way or another made these changes.  Things changed because human behavior changed.  

I suppose that the fact of human malleability and inventiveness was the point Michael Polanyi was trying to make when he said that, “Theories of evolution must provide for the creative acts which brought such theories into existence.”

Jim says in his blog entry, “I guess I’m not persuaded by these why-the-elephant-got-its-trunk stories.”  He’s not alone.  Gould called these speculations about how certain human traits came about as “just-so stories.”  Like Kipling’s efforts, the evolutionary psychologist simply invents seemingly plausible explanations for why we are the way we are with not much more evidentiary basis than the original stories.  That is, by proposing a mechanism for how some physical or behavioral trait could be adaptive, the evolutionary psychologist feels that he have fully explained its origins.

One of my favorite just-so stories is “How the Little Girl Came to Like the Color Pink.”  In 2007, Anya C. Hurlbert and Yazhu Ling of the Institute of Neuroscience and School of Biology and Psychology of Newcastle University, UK, published a study called “Biological components of sex differences in color preference.”  The researchers concluded that little girls’ preference for pink “arose from sex-specific functional specializations in the evolutionary division of labour.”   They reasoned that, as the gatherers in the hunter-gatherer society, female brains were specialized “to facilitate the identification of ripe, yellow fruit or edible red leaves embedded in green foliage.”  As a consequence, so the argument goes, little girls prefer pink.  

It’s a nice story, but it’s got more holes than a sieve.  First, we have zero evidence that only the distaff side of our prehistoric ancestors did all the gathering.  We just don’t know.  Second, preference is not the same thing as ability to distinguish.  Third, not all ripened fruit is red or yellow.  Dates, figs, olives and pears – all of which existed in the Pleistocene – are obviously not red or yellow.  Some berries are red, but many kinds are not.  Indeed, while almost all blue or black berries are edible, half of all red berries – such as the holly berry – are poisonous.

In addition, these color preferences are clearly a recent development and not an adaptation originating with the first humans.  In 1918, the Ladies' Home Journal wrote: "There has been a great diversity of opinion on the subject, but the generally accepted rule is pink for the boy and blue for the girl. The reason is that pink being a more decided and stronger colour is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl."  And then, the Sunday Sentinel in 1914 told American mothers: "If you like the colour note on the little one's garments, use pink for the boy and blue for the girl, if you are a follower of convention."  It wasn't until the 1940s that the modern gender associations of pink for girls became accepted in this country.  For the full story, see Pink and Blue: Telling the Boys from the Girls in America by Jo B. Paoletti.  So, it seems then that pink is not all that biologically girly.

My other favorite is “How the Human Male Got His Fist.”   According to University of Utah researchers Michael Morgan and David Carrier, hands evolved to punch faces, and faces evolved to take punches.   These researchers assumed that no sooner had Pleistocene males dropped out of the trees than they started whaling away at each other – mostly over women and food.  This is another a post hoc fallacy – because our hands can be effective weapons, then they must have evolved for that purpose.  

Again, the same problems emerge.  We don’t know how much our ancestors fought.  And we certainly don’t know whether they were pugilists (and did they follow the Marquess of Queensberry rules?), or whether they fought some other way, like scratching and gouging and rolling around in the mud.  Beyond that, the possibility that the ability to form a fist might by an evolutionary byproduct of a hand naturally selected for other reasons was not considered.  Again, this is just a story based on a lot of speculation.  As far as we know, the hand was no more designed by natural selection to punch people in the face than the nose was formed to hold spectacles.

As all this demonstrates, ultra-Darwinism is not good Darwinism.  

One final observation:  not only did Darwin’s theories differ from those of the latter-day Darwinists, he viewed his subject, nature and the world, entirely differently than they.

First, he did not believe that human existence was a war of all against all for the survival of only the fittest.   Indeed, he had quite a different vision:  “As man advances in civilization, and small tribes are united into larger communities, the simplest reason would tell each individual that he ought to extend his social instincts and sympathies to all members of the same nation, though personally unknown to him. This point being once reached, there is only an artificial barrier to prevent his sympathies extending to the men of all nations and races.”

As for his broader view of life, one might consider his famous final sentence of The Origin of Species.  Referring to his theory of evolution, he said:  “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” 

Elsewhere, in one of his journals he echoes the same sentiment:  “Among the scenes which are deeply impressed on my mind, none exceed in sublimity the primeval forests undefaced by the hand of man; whether those of Brazil, where the powers of Life are predominant, or those of Tierra del Fuego, where Death and Decay prevail.  Both are temples filled with the varied productions of the God of Nature: no one can stand in these solitudes unmoved, and not feel that there is more in man than the mere breath of his body.”  Loren Eiseley in his essay, “Science and the Idea of the Holy,” says that, although Darwin was an agnostic, his writing expresses a “feeling of awe, of dread of the holy playing upon nature.” 

But, ultra-Darwinist Richard Dawkins sees things quite differently:  “The universe we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil, no good, nothing but blind, pitiless indifference.”