The vast majority of science-related literature pertaining to behavior incorporates unwarranted inferences to and assumptions of its evolutionary origins. With few exceptions, the popular articles, books, videos, and websites that present information about behavior will make a couple of particular assumptions. One of these assumptions is that it’s scientifically uncontroversial to attribute the cause of any number of behaviors to genes or brain modules. The other is that there needs to be a teleological story, a sort of narrative about purpose, to accompany the assumption that a behavior evolved biologically. While there may be room for disagreement about what exactly constitutes a qualifying nature for the necessity of making the assumption that a behavior evolved, even among those who make it, there is almost never a challenge to the idea that some variant of the assumption must be made.
The endeavor of exploring this topic here stems partly from a concern that these kinds of assumptions, when left unchallenged in the public eye, can unintentionally lead to a miscommunication of science. In some cases, a lack of challenge to particular assumptions can even serve to bolster racist and sexist attitudes, as some groups will point to science-related literature in support of their views. For these reasons, it’s a worthwhile effort to understand some of the scientifically and philosophically normative impediments to these sorts of assumptions as well as the subsequent implications for the necessity of making them.
Maybe a useful way to think about this is: There are two categories of objections to these types of assumptions; the first category calls into question, the compatibility that these assumptions might have with evolution; the second category is what could be characterized as methodological concerns with the kinds of scientific evidence employed in support of the assumptions. Before getting to the objections, it’s going to be useful to give a very brief review of some key terms and ideas from evolutionary biology. The reason for the review stems from the contention that the lack of challenge to these assumptions about behavior and evolution can be at least partly explained by a misunderstanding of evolution.
The modern understanding of evolution includes four primary forces: mutation, recombination, random genetic drift, and natural selection (Michael Lynch, On Evolution By Non-Adaptive Mechanism 2012). The first three forces are well-understood and quantifiable phenomena; the last force is not so well understood and not quantifiable.
Mutation is the force that creates variation in a genome. It primarily affects the integrity of parental nucleotide sequences. When DNA is in the process of copying itself, very small differences from the original occur. A mutation is a duplication, insertion, or deletion of part of an existing sequence of molecules within a strand of DNA.
Think of it as though you were copying a line from a script and one of the words appeared twice where it shouldn’t or otherwise the word didn’t show up in the copy at all. Maybe even in some cases, an alternate word popped up in the sentence to take the place of the original. Now, imagine that you made a bunch of copies of the same line and after awhile you noticed several different versions of the line occurring repeatedly among the many copies.
Mutations are almost neutral with respect to their overall effect on any living population (Futuyma Evolution p. 266). The late, highly-influential, geneticist Motoo Kimura first put forth the Neutral Theory of Molecular Evolution in 1968. His prestigious student, Tomoko Ohta, further developed the theory into the Nearly Neutral Theory of Molecular Evolution. One of Ohta’s significant contributions to the theory was to show that slightly deleterious mutations were substantial aspects of evolution.
Whenever we’re talking about a physiological change in an existing population or species (through an individual variant), we’re in a sense talking about mutation. Though it’s worth noting that mutations will usually go entirely unnoticed and so for most of them, we won’t have much to say. Nevertheless, they’re still a very important force for evolution, in the long view. It’s useful to know that when thinking about the kinds of change that evolution can create, mutation ends up serving as a kind of constraint for what we might otherwise imagine that evolution can do.
The next primary force for evolution is called recombination. This force is also sometimes referred to as genetic reshuffling. On occasion, a chromosome will exchange genetic material from different regions within itself or sometimes with another chromosome. When this happens, we call it recombination (see Suzanne Clancy, Nature 2008).
As a way to think about this, imagine an organism’s genome as a kind of improvisational play. In this scenario, mutation would constantly make slight variations to the dialog every time the play is read, but recombination would take whole events from the play and put them in a different order. Its parts remain familiar, but you’d still say that it’s a different play altogether. If not a play, think of a film. If DNA were showing a typical chronological story in the style of Richard Linklater, recombination would be the atypical, anachronistic, Quentin Tarantino style of DNA.
Yet another primary force to understand and bear in mind is known as random genetic drift. One of the most important aspects of random genetic drift as a force in evolution is that it is highly quantifiable. This makes it very well understood and a force to be reckoned with whenever reasoning about evolution.
As a consequence of the large quantities of genes that exist within any given population of multicellular organisms, it ends up being pure, statistical chance that governs whether or not any particular gene will be passed on to become a permanent part of the genome of that population. In population genetics, this feature is called fixation. Random genetic drift also happens to have almost no effect on an organism’s reproductive success or survival, and it is, in fact, an unambiguously non-adaptive force in evolution. That’s to say: it is not beneficial to the organism.
One of the important known features of population genetics is that the physical size of an individual organism has an inverse correlation with the quantity of its reproductive population. So, where individual organisms tend to be larger, the quantities of their populations tend to be smaller. It’s also the case that the smaller an overall quantity of individual organisms in a given population happens to be, the greater the odds that particular genes will become fixed to that population’s genome. This is true regardless of whether the genes that become fixed provide any beneficial effects or not. In fact, fixation even happens with genes that are somewhat harmful to a given population. This fact was part of what Tomoko Ohta’s work showed, as previously mentioned.
There may be a way to get a better picture of random genetic drift. Try thinking of a jar with ten M&M’s in it. Suppose that there are five colors to start with, two of each. If you were to pour half of the M&M’s into another jar and eat the rest, you might end up with two of one color, none of another, and only one of each of the remaining colors. Imagine that the M&M’s could self-replicate at this point so that you had a total of ten again. The difference now is that the ten you have, are duplicates of only the five that were left after you had eaten the first half. Suppose that you were to repeat the process of pouring half into the other jar and eating the rest. This time around, one of the other remaining colors ends up not making the transfer to the jar, leaving only three colors from the original five. Pretend that they could self-replicate again at this point. By now, you would notice that one of the colors had quickly become overwhelmingly abundant inside of the jar, and that happened simply because chance had allowed that color more opportunities to self-replicate. Now when this effect happens to genes, it’s called random genetic drift.
Which brings us to natural selection. As it happens, natural selection is the most talked-about force. Despite its convoluted definition and highly questionable level of contribution to evolution, it is commonly thought of as holding a status of dominion over all of evolution. Often times where it can be found, people colloquially use the terms natural selection and evolution interchangeably. Nevertheless, natural selection has a much more questionable role in evolution than its three other counterparts.
It might serve to illustrate part of the problem by drawing upon examples from Douglas Futuyma’s work. Futuyma is an evolutionary biologist from Stony Brook University who’s written a prolific textbook for undergraduates titled Evolution. Here’s a definition of natural selection from its glossary:
[The differential survival and/or reproduction of classes of entities that differ in one or more characteristics. To constitute natural selection, the difference in survival and/or reproduction cannot be due to chance, and it must have the potential consequence of altering the proportions of the different entities. Thus, natural selection is also definable as a deterministic difference in the contribution of different classes of entities to subsequent generations. Usually, the differences are inherited. The entities may be alleles, genotypes or subsets of genotypes, populations, or in the broadest sense, species. A complex concept; see Chapter 11.]
As a point of clarity, it’s worth commenting that, alleles are the variants for single gene mutations. Think back to the script-copying analogy: when you copy the same line a bunch of times, you end up with several different versions of the line that occur repeatedly among the total set of all of the copies. Genotypes then are the variants of sets of multiple genes among individual organisms. To continue on, as the glossary suggests doing for further elucidation of the concept of natural selection, here’s how Chapter 11 begins:
[It is this theory that accounts for the adaptations of organisms, those innumerable features that so wonderfully equip them for survival and reproduction; it is this theory that accounts for the divergence of species from common ancestors and thus for the endless diversity of life. Natural selection is a simple concept, but it is perhaps the most important idea in biology. See also genic selection, individual selection, kin selection, group selection.]
There is a small paradox in the sense that natural selection seems to be both a complex and a simple concept. It is supposed to account for all beneficial changes to organisms, though it’s unclear how this concept should be quantified. It accounts for the divergence of species from common ancestors, except in the cases that it doesn’t (e.g. random genetic drift). It may also include the consequences for behaviors which have beneficial and/or detrimental effects on survival or reproduction (e.g. individual selection, kin selection, group selection). Natural selection may include all of that, just so long as chance has nothing to do with any of it. It’s uncertain how clear all of that is. In a practical sense, if someone were to simply accept the textbook description of natural selection for what it is, they could be forgiven for coming away with the impression that it is just a synonym for evolution. Though, anyone teaching evolution in a nuanced way should absolutely tell them that this is not the case.
Elsewhere, natural selection has been hypothesized as a force that reduces the rate of mutations in genomes (see Lynch et al, 2012). So, it is still a point of some controversy within the big science of evolutionary biology. The literature that’s aimed at general audiences about this topic doesn’t often reflect this controversy.
An alternative interpretation of natural selection that might be worthy of consideration, could make reference to how people actually use the term in practice. If the interpretation were a reflection of the term’s typical usage, natural selection might instead be characterized as a hodgepodge of ahistorical inferences that people make about any characteristic for any organism.
In highlighting some of the problems that come out of the textbook understanding of natural selection, it bears mentioning that Futuyma’s text was perhaps unfairly picked when granting that similar descriptions can be found throughout the literature on biology. Futuyma’s text was picked partly for its strength and clarity, and partly for its concision. It would be unfair to misrepresent Douglas Futuyma, so it’s necessary to point out that he is not at all omitting the other forces of evolution in his book. The unflattering example above was deliberately picked to make a broader point, but his book (Evolution, 2nd edition 2009) provides an otherwise indispensable understanding of the topic and it would benefit anyone interested in the subject to read it.
As mentioned before, there are two categories of objections that can be made about tethering behavior to evolution by making assumptions about a physiological cause and a teleological story. Anytime you hear a story about how a trait evolved, especially a behavior, there needs to be some question about its compatibility with evolution. Is it possible for a specific behavior to evolve? If so, how?
In a cursory sense, there isn’t much that seems wrong with assuming that most or even all behaviors have been the consequences of evolution. More to the point, it’s not a fantastic leap to make the inference that brains are among the products of evolution. We can be sure that they are. Apart from that, we have accumulated mountains of evidence that brains are the organs that facilitate behavior. So, of course, it follows that human behavior in a broad sense at least is also a product of evolution. Challenging that well-supported inference is not at all warranted.
On the other hand, as an example of a point of legitimate criticism, someone might object to the pronounced tendency in popular culture–extending right into scholarship–to assign a story about an adaptive purpose to almost any specific behavior. Adaptations in biology have the specific meaning of changes in populations of organisms that benefit survival or reproduction. As these stories are told in ways which characteristically attribute beneficial outcomes (such as self-preservation or sexual reproduction), to any number of behaviors, typically there is also an implication that the reason that behavior B exists is to promote outcome O. In other words, there is a common purpose or intent in the evolved characteristics of organisms. These are often attractive explanations and when we make sense of them, they can generate a positive affective response. Put slightly differently, it feels good to understand these kinds of teleological stories. For purposes here, these kinds of stories will be referred to as selectional narratives.
These selectional narratives are seldom challenged and there are in fact, fields of academia that are creating and establishing them as a part of their regular practice. It’s primarily sociobiology and evolutionary psychology that engage in this practice. Nevertheless, there are some problems with these narratives that people studying evolution generally, need to concern themselves with.
For example, if someone wants to say that something like a peacock’s tail was selected for by extremely fickle peahens (Matt Ridley – The Red Queen, Chapter 5), they need to be able to point to a developmental pathway by which peahens have evolved non-random choice, with respect to mate selection. Put another way, there needs to be something that distinctly changes in peahen brains and causes them to alter their choices in the ways that they do. The problem is, this can’t really happen because far too much would have to physically change from one generation to the next for there to be any kind of adaptive motive to act upon. Evolution is an extremely slow process. Further still, when you think about how peacock tails became so elaborate and decorative, in the grand scheme of things, it just doesn’t make sense to imagine that there was some sort of advantage to it.
To take another example, some have wanted to say that ants have a biochemical language with words that they use to communicate with others (E.O. Wilson & Bert Hölldobler – The Ants, 1990). This suffers from a similar set of problems in a sense. Most importantly, we can’t establish that there is a way for ants to facilitate and interpret that kind of communication. Ants only have a cluster of maybe 250,000 neurons to work with, which is far less than any other species that we might suspect of having anything like a language. Ants are also only working with two or three biochemicals apiece, which doesn’t provide enough statistical variety to create anything like a discernible language. Certainly not one that an organism without a brain could wield. It isn’t even generally recognized that other kinds of apes have this sort of capacity in any literal sense.
It should probably raise eyebrows when someone says that bright colors are used to ward off predators and attract mates. Even without taking into account the visual perception of other organisms as different from each other, stories like those should seem obviously flawed (Matt Ridley – The Red Queen, Chapter 5).
Examples with reference to human behaviors are out there as well. There have been researchers who wound up concluding that women have evolved to love money more so than men, presumably as a strategy for securing resources for offspring (Matt Ridley – The Red Queen, Chapter 8, p.267). However, this kind of inference shouldn’t be taken seriously without first establishing that this is a real phenomenon. Survey data, as the only known method for making that kind of establishment, is prone to its own set of problems, but we’ll set those problems aside. Even if the phenomenon can be shown to be real, it would still be necessary to reject the cultural explanations that might account for it. If women love money because it’s socially beneficial in the present, why do we need a more complex motive for that behavior to evolve biologically (e.g. strategy for securing resources for offspring)? Suppose that women could evolve this characteristic, then you’ll still need to find a developmental pathway that excludes men from inheriting this characteristic as well. It’s common knowledge after all, that men carry the odd Y chromosomes, while women only carry the X chromosomes that are shared among the sexes. How can the heritability be distinct to women?
A prominent evolutionary psychologist (David Buss, working with a less well-known colleague), put forth the idea that men stalking women was an evolved adaptation to solve mating problems at a non-specific time in our evolutionary history (Joshua Duntley & David Buss 2010). Those who know a little about biology might notice that there isn’t any possible way for something like this to evolve, even apart from any questions about the conflation of the modern crime of stalking with a conscious strategy from prehistory for population growth. This kind of conjecture makes for an example of a selectional narrative that’s not very scientific, to put it charitably.
All of these are real examples of the kinds of selectional narratives that appear in a variety of science communication media on a fairly routine basis. They’re all ideas that have been supported by evidence coming out of somewhat dubious studies and in some cases, celebrated books about evolution. To a discerning eye, however, the ideas about evolved behavior only seem to become more strange as one looks at them.
Apart from the ever-looming questions about how physiological causes of behaviors or teleological stories about them, might fit in with the broad forces of evolution, there are also a plethora of methodological concerns about the evidence that’s used to support those kinds of inferences. Chiefly among the concerns is the drive of researchers to beg the question about the purpose of evolved behaviors. That’s certainly a way for reasoning about evolution to go awry. If Einstein had supposed that the force of gravity had a purpose, we likely wouldn’t have thought as much of him. Why then, do we so easily ascribe intent to the forces of evolution?
One of the selectional narratives that people find very compelling, happens to revolve around the presumably adaptive functions of our affinity for recognizing patterns. On the one hand, pattern recognition, as an adaptive function, seems fairly intuitive. This, of course, isn’t a license for prima facie consideration. On the other hand, there is a phenomenon known as apophenia, in which people spontaneously recognize patterns in a wide variety of things, including instances where there isn’t any true relationship to be found. It doesn’t take a stretch of the imagination to infer, at least the possibility, that this phenomenon might affect how we think about evolution. In many cases, it could be that the way we conceive of what benefits organisms and their chances to reproduce or survive is a byproduct of this kind of pattern recognition. By presupposing that a particular trait is adaptive and relating it to traits found in different species living in different environments, we can make some interesting patterns that also might be fallacious.
The philosopher Richard Boyd of Cornell University provided many detailed points about the variety of methodological concerns for the evidence that gets used in support of the associative connections that are so often made between behavior and evolution. At the 2011 ‘Debating Darwin’ conference at UC Berkeley, Boyd showed that certain presumptive practices are harmful to the development of fields of study that are related to psychology. He also drew some lessons for the philosophy of science — an area of study in which Boyd specializes — that have broader implications for science generally. In addition to some of those lessons and concerns, there are some other methodological concerns worth pointing out as well.
Often the ideas about evolved behaviors fail to respect the principle of parsimony or Occam’s Razor. This is the scientific principle that the hypotheses with the least number of ill-supported assumptions should be sought out to be tested or falsified first. This sometimes manifests in the characteristic treatment of behavior in science communication, to not give serious consideration to the idea that the behavior in question, isn’t an adaptation. If there is a desire to attribute a kind of behavior to the power of natural selection, it’s necessary to be able to rule out the idea that it came about randomly or that it isn’t beneficial. That is, after all, what parsimony would demand.
It is enormously commonplace to make unwarranted inferences about the purposes of behaviors, usually by assuming that something like an innate brain function or module exists. Brain modularity is still controversial and nothing like an innate module has yet to be established with consensus. Some may think that fMRI data supports brain modularity; not so (see Carol Tavris, 2012). Nevertheless, selectional narratives require something physiological that can perform the functions that are alleged to be done by modules, in order for the stories to make sense. (Boyd, 2011)
There are often problems with the reasoning that is put forth in the various media for communicating science. For example, it’s typical to find a book or article that makes use of a kind of reasoning which anthropomorphizes the extremely slow, intergenerational, chemical process of evolution by endowing it with sometimes conflicting intentions. (e.g. bright colors evolved to attract mates and repel predators).
Sometimes supporting evidence comes from studies that have used optimality models. This is essentially a cost/benefit analysis, which is typically used in economics, but in this case, applied to animal behavior. In optimality models, animals are by some measure, assumed to be rational which is a questionable proposition, to say the least. (Boyd, 2011)
One assumption that goes on a lot of the time is that behavior is basically non-malleable (Boyd, 2011). So, whatever behavior evolved at some point in the past has stayed that way. As discussed earlier, this pushes past the question of how the behavior evolved in the first place.
Some of the claims in the popular and academic literature about evolution rely upon the use of comparative biology. This is the idea that an inference about one animal can be carried over to some different kind of animal. For example, someone might intuit a reason for a particular behavior in gorillas and use that to explain a different behavior in humans (Boyd, 2011).
Some of the science that’s used to support selectional narratives relies heavily on survey data. There is a good reason to give very careful consideration to the methods used in the surveys because there are so many ways that the data can end up being not particularly objective. Richard Boyd also pointed out that survey data about personal preferences doesn’t reflect what people actually do.
In some cases, authors conflate post hoc interpretations of a study with successful evidence for a specific model of behavior. This can often be seen from researchers that are interested in kin selection for example (Boyd, 2011). A version of the Texas Sharpshooter Fallacy should be something capable of shedding light on the danger here. The name of the fallacy comes from an allegory where a blindfolded man is shooting buckshot at the side of a barn. After the fact, a passer-by notices the marks on the side of the barn and takes it upon herself to draw a large bullseye centered over the largest cluster of marks. The passer-by then concludes that the bullseye is the spot that the blindfolded shooter must have been aiming at all along.
There are scarcely any attempts to identify genotypic counterparts in relation to phenotypic behaviors. Phenotypes are any identifiable characteristic in a population of organisms other than the genetic material itself (e.g. voice, eyes, nose, etc.). So, in other words, when some characteristic is observed, there often isn’t an attempt to identify a group of genes that might show that the trait has, in fact, evolved.
In spite of a wide variety of behaviors being commonly described as beneficial products of evolution, there are enormous challenges to those kinds of descriptions. After reviewing the primary forces of evolution, it’s apparent that the assumptions about the heritability of behaviors are not to be taken for granted. In carefully examining the reasoning for teleological stories or selectional narratives, it’s revealed to be the case that they are unnecessary or otherwise incompatible with evolution. While behavior is, in a broad sense, the result of evolution, there isn’t sufficient evidence to support any claim that behaviors serve underlying evolutionary purposes. On the contrary, there are many reasons to think that most behaviors change in ways that can’t be accounted for by evolution.
There are good reasons to resist the temptation to say that behavior is the product of evolution. Behavior is something that we change constantly so we might look towards the cultural and social explanations for behavior as appealing alternatives. It would be useful for people to be capable of thinking critically about arguments in this vein because although ideas about innate behaviors don’t necessarily lead to bolstering racist or sexist attitudes, they certainly can. Making a more proportionally accurate representation of the arguments about this topic accessible to a general audience seems like a worthwhile effort.
Evolution is something that’s ripe for a greater public understanding. This is likely a daunting task because it’s a large enough area of science for there to be a great deal of misunderstanding even among its experts. Evolution is a topic that should be presented with a level of humility and depth so that the general public doesn’t become overconfident with misunderstandings about biology. Solving the problems in this domain are likely to yield some broader solutions for both philosophical and scientific understanding generally and we will all be better for it.
- Richard Boyd – Evolutionary Theory as Methodological Anesthesia: Methodological and Philosophical Lessons from Evolutionary Psychology (2011) [Conference Title: Debating Darwin] https://youtu.be/AluTvl8M4Us
- Michael Lynch, et al.- On Evolution By Non-Adaptive Mechanism (2012) [Conference Title: Darwin In the 21st Century: Nature, Humanity and God] https://youtu.be/Mc0h0l-eHVA; The Drift-Barrier Hypothesis and Mutation-Rate Evolution (2012) http://www.pnas.org/content/109/45/18488
- Douglas Futuyma – Evolution (second edition 2009)
- Matt Ridley – The Red Queen: Sex and the Evolution of Human Nature (1993)
- E.O. Wilson & Bert Hölldobler – The Ants (1990)
- Suzanne Clancy – Genetic Recombination (Nature, 2008) https://www.nature.com/scitable/topicpage/genetic-recombination-514
- Joshua Duntley, David Buss – The Evolution of Stalking (2010 & 2012?) https://link.springer.com/article/10.1007%2Fs11199-010-9832-0
- Wikipedia article on Tomoko Ohta – https://en.wikipedia.org/wiki/Tomoko_Ohta
- Carol Tavris – A Skeptical Look at Pseudoneuroscience (2012) https://youtu.be/xwxdgZeIdqI