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Evopsychopathy 4: Adaptive scenarios

Last updated on 2 Jan 2013

Sorry for the gap, RL intervened. This is going to be the hardest one of these to write. And if you think tl;dr, fair enough. But it’s a crucial aspect to discussions of EP and SB.

Although I think that Darwin’s greatest idea was common descent as an explanation for the relationships of organisms, I am very much in the minority here. Most people take it as read that Darwin’s best idea was natural selection. However, ideas very like natural selection (NS) had been around for a long time, unsurprisingly since they are employed in animal husbandry (the artificial/natural distinction is, well, artificial). What was novel about Darwin’s and Wallace’s use of NS was that it caused change in species, or so they thought. These days the consensus appears to be that species originate independently of natural selection processes, and selection changes the ecological adaptive features of the species rather than the isolation of species from other species.

That is by the way, however. Almost everyone in the evolutionary psychology movement and prior sociobiologies, at least after the turn of the 20th century, thinks that natural selection accounts for human behaviours. The issue is again a haggling over the price: how much and how often, and of what? So a major issue in SB4.0 is the role of adaptive explanations: what should we propose, how do we test them, and what is the default explanation: chance or selection? That is what this post is about.

EP and SB have typically presented explanations of human behaviour based upon the adaptation of those behaviours. Everything from mate choice to rape to religious belief to cognitive deficits are explained in this fashion. I do not propose to examine any of them here. What, as a philosopher, I find interesting are the assumptions underlying them, and how they might fail. Scientific research has a number of mathematical and experimental techniques to determine if something is the outcome of selection: selective sweep analysis, experimental work on cases, and phylogenetic comparisons. Each seems to have problems.

To determine if something is the result of a selection process, one has to have a good idea of what it is that could be the target of selection. The Standard Answer is that genes are, but often as not we do not yet have much of an idea what genes are responsible for what traits, and what the norm of reaction (the way the genetic trait is expressed) might be. This has always been a problem for evolutionary genetics, and indeed for a long time, a “gene” was simply a heritable trait (or rather, what underlay a heritable trait). As once noted by Lewontin, phenotypes are what Mendelian genetics studied.

So EP/SB has to indirectly approach selectionist explanations. Often they do not, but the better studies have to face the same methodological issues that every other evolutionary explanation does:

  • We do not know the genes for most traits (and few traits are single gene traits, even for metabolic diseases),
  • We often do not know much about the environment in which selection is thought to have occurred, and when we do it is global rather than local (e.g., a snail is not affected by the climate of the whole world, but by the microclimate of its hillside or valley),
  • Information about the past is often fragmentary, leading to easy and cheap narratives that happen to suit the researchers,
  • Information about the present is also often fragmentary and partial, and
  • If a trend is seen in the data, it is often unclear when this is due to drunkard’s walks (chance) which can deliver directionality over moderately long periods, and when it is due to selection (which can be chaotic if the environment is).

Moreover, the standard EP approach relies upon an atomisation of traits that is more based on expectation than upon observational data. For example, and the key issue for EP for humans, the “massive modularity hypothesis” requires that the cognitive and psychological traits are parcelled into discrete and relatively independent modules. There is a parlous amount of evidence for this outside sensory modalities. Yes, vision (and possibly hearing and the other senses) is quite modular. It is also very old, going back perhaps to the Cambrian, so given that things with eyes need to see well, we might expect the visual module to be independent of the other neurological traits.

But modularity is not required by evolutionary theory; in fact it seems more to be a matter of convenience for researchers than anything else. A complex multifactorial system can be modified simultaneously in many ways by selection, so long as the factors (i.e., the underlying genetics) are heritable, because what NS requires is that things be heritable for them to be adaptively changed by NS. Think of an organism as a system that develops like a sprung mess of rigid poles connected by elastic bands. You can move several at once and the whole system will reshape (this is called tensegrity by Buckminster Fuller, as a punishment for thinking about these things). The rigid poles are the heritable genes, and the rubber bands are the norms of reaction.

A tensegrity example

[A tensegrity example, from here.]

So we might expect that you can modulate behaviours (or at any rate d-behaviours) by adjusting a few genes at once.The requirement that d-behaviours (or for that matter expressed behaviours) should be isolated and independent of other traits is not required. Gould and Lewontin referred to this as “inappropriate atomisation”. The “adaptationist programme”, they wrote (Gould and Lewontin 1979: 585), starts with this step:

An organism is atomized into ‘traits’ and these traits are explained as structures optimally designed by natural selection for their functions. For lack of space, we must omit an extended discussion of the vital issue: ‘what is a trait?’ Some evolutionists may regard this as a trivial, or merely a semantic problem. It is not. Organisms are integrated entities, not collections of discrete objects. Evolutionists have often been led astray by inappropriate atomization, as D’Arcy Thompson … loved to point out.

The emphasis upon isolating single genes or alleles is a case in point. No gene does what it does in a vacuum (in fact, put DNA into a vacuum, and it will simply sublimate and denature). It needs not only other genes but a developmental organism in an environment it affects simply by developing. I can’t stress this truism enough. What a gene does depends on the system it is a part of.

Modularity, whether of genes or organs or neurological systems, is only ever a conceptual abstraction. Cognitive modularity, however, was based upon the presumption that to be the subject of selection, a cognitive process had to be isolated from other processes in order to be optimised, to be encapsulated: modules were shallow so they could produce outputs without much delay based on the types of inputs they were optimised to receive, domain specific to they only received one type of stimulus or input, inaccessible so they were not affected by content or dispositions elsewhere in the brain, and so on. Later work showed that even those exemplars of modularity, such as are tested by the Wason Test, of reasoning are able to be moderated and even interrupted by contents of the cognitive system

So, enough about what fails or is problematic about EP and SB. What about what works?

Some may take issue with (PZ has) my claim that only selection can generate complex d-behaviours. A brief word is due. We know that selection (as an instance of general sorting processes) can generate complexity of behaviours. We know that a lineage or population that has some suite of behaviours can randomly attain a more complex behaviour. I am not suggesting that random variations within a population of already high complexity cannot produce such behaviours. But over the longer term, what randomness giveth, randomness will taketh away. For a trait to persist in a population (note, in a population, not a lineage of species over large periods) and to go to fixation if the population is of any size it is more often than not, much more often, due to selective pressures on those behaviours than to chance. And where using chance as a “null hypothesis” generates few if any hypotheses of what did happen that are testable, selective explanations do generate many, often very specific, hypotheses that are testable.

There is a real issue (see here, here and here; the work that convinced me of this is Fidler’s) with null hypotheses anyway. A “null” hypothesis is, simply put, the hypothesis that the researcher or the researcher’s community defaults to in the absence of anything else. In short, the null hypothesis is what the community of researchers is comfortable with, and since this is not really constrained by data (there are an indefinitely large number of potential nulls) testing between a null and positive hypothesis is at best a very localised test.

But leave this to one side: if chance explanations of a d-behaviour explain it arising, it can equally explain it disappearing. To explain the persistance of a complex d-behaviour, selection is pretty well it. As was long ago noted the origins of the raw material of selection are down to accidental changes, but not their retention.

But that is not the whole story. Once you have a reproducing populations of organisms of overall high fitness, individual d-behaviours may wander about stochastically. This can be true of a single variable, so long as the overall or general fitness of the population mean is high enough. So it comes down to being able to establish whether the d-behaviour is likely to lower the fitness enough that selection pressures will overcome the randomness of mutation and recombination. And there is no principled answer to this – it relies upon the facts of the case; the boundary conditions and the number and relation of the variables. Sergey Gavrilets (1997, 2004, see Wilkins 2007) has noted that in a correlated or smooth fitness landscape (such as we might expect nearly all species to exist in when in their ordinary environments) there are what he calls “holey landscapes” (see figure), which are components of fitness space that are of roughly equal fitness, and which are connected in various ways to higher and lower fitness components. In short, in a sufficiently high dimensional landscape, a population may drift around at about the same fitness (in other words, its d-behaviours can shift stochastically) so long as the fitness of that population remains about the same. So this implies that a d-behaviour can be both the result of selection relative to its absence, but also the result of chance relative to equally fit alternatives. The chance/selection dichotomy is misplaced. Both can be true simultaneously.

Gavrilets holey

So to take on the adaptationist program (or “programme” as Gould and Lewontin spelled it) is not to make a mistake. It is to make an epistemic bet. Cheap and simple adaptive hypotheses must be treated with derision, of course, as they must in every aspect of science – this is not a critique of EP as such, but of bad science. But good ones must be treated as working hypotheses. There’s a big literature on testing and choosing between models. I shan’t bore you with that here (I find the Akaike Information Criterion approach perplexing, for example, which probably says more about me than it). The point is that EP/SB is not required not to be non-adaptationist as a null hypothesis.

In the light of all this, I suggest that so long as we test our adaptive scenarios, and do so realistically on the basis of phylogenetic bracketing (to ensure we are actually dealing with a d-behaviour) and on the best data (especially that of neurobiology and cognitive psychology), EP/SB (or SB4.0 at any rate) has a right to be adaptationist, and that alternative approaches must be justified. Adaptation is the “null hypothesis” in the case of complex d-behaviours, subject to the qualifications I make above.

As once said, there’s the bit where you say it and the bit where you take it back. Adaptationism does not explain, I believe, the persistence of a trait across phylogenetic bifurcations – that is, in the case of evolutionary lineages. Or rather, it can, but only in the sense of it being “evolutionarily conserved”. For example, the structure of the genetic code is highly conserved. Although there are some 15 variants across the whole of life, they vary only in details. The having of the “universal” code is highly fit, and variants tend to be eliminated. Many developmental, phenotypic, physiological and cytological structures are highly conserved. Why? The answer has to be something like: if you deviate from this state, your fitness is lowered, just because it is the default or modal state. So the having of, say, a particular social disposition among primates can be maintained because the having of that disposition increases your fitness – deviants get fewer mating opportunities. Creatures inveterately wrong at following the norm have a pathetic, but praiseworthy, tendency to die before reproducing their kind…

Which leads us to a final point about adaptation: the what it adapts to. Good Old Fashioned Adaptationism (GOFA*) always presumed that what the fitness assigning process was had to do with the ecological context of the organisms. But equally, or in the case of highly adapted creatures like primates, predominantly, the fitness assigning process is social. You are fitter because your d-behaviour fits a potential mate or social conspecific. Here I think the emphasis has been more productive. Others will disagree, but as the Buss Lab’s defence shows (Confer et al 2010), there are some useful results in so doing.

* Not to be confused with GOFAI, which is a position in artificial intelligence philosophy.


Confer, Jaime C., Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M. Buss. 2010. Evolutionary psychology: Controversies, questions, prospects, and limitations. American Psychologist 65 (2):110-126.

Gavrilets, Sergey. 1997. Evolution and speciation on holey adaptive landscapes. Trends in Ecology & Evolution 12 (8):307-312.

———. 2003. Perspective: models of speciation: what have we learned in 40 years? Evolution Int J Org Evolution 57 (10):2197-2215.

———. 2004. Fitness landscapes and the origin of species, Monographs in population biology; v. 41. Princeton, N.J.; Oxford, England: Princeton University Press.

Gould, Stephen Jay, and Richard C. Lewontin. 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proc R Soc Lond B 205:581–598.

Wilkins, John S. 2007. The dimensions, modes and definitions of species and speciation. Biology and Philosophy 22 (2):247 – 266.


This series:


  1. This, I think, is the key: ‘Adaptation is the “null hypothesis” in the case of complex d-behaviours, subject to the qualifications I make above.’

  2. How do you distinguish between a good and a bad adaptive hypothesis? Considering the goal is allegedly to describe what happens in nature, that decision would depend on comparing the hypothesis with evidence from the natural world instead of comparing one abstract model with another. Or, at least, isn’t that alleged to be what the purpose is?

    Natural selection is a profoundly ambitious theory that purports, in its most extreme advocates, to describe a sort of force behind, literally, trillions and trillions of wildly different events and circumstances resulting in variable rates of reproduction, resulting in change in and among diverse populations of individual organisms. Even as convinced and credible an advocate for it as Richard Lewontin has pointed out that large numbers of selective scenarios were too subtle to quantify and, I’d assume, observe, and that they happen very subtly over a long period of time. I don’t see any way to evaluate such a thing, certainly not with real science or by direct or even indirect observation of nature. In the end I’m a lot more convinced that natural selection is what appears to be behind those events due to habits of thought among biologists and so-called scientists, than that there is any real thing that is “natural selection”. I think those trillions of events and circumstances are probably too diverse and disparate to be attributed to a single imagined force.

    I think there is a good deal of professional and social coercion behind the hegemony of natural selection, which will be found to inhibit the development of other, perhaps more targeted and evidence based, explanations of how evolution happened and happens. Not all of it, but a good deal of it for extra-scientific ideological purposes.

  3. I like your list. May I suggest one addition?

    – We often don’t know whether the trait in question even has a significant genetic component or whether it’s just nurture.

    On of the problems with the adaptationist approach is that that it not only skips over other genetic explanations but also leaps over possible nongenetic explanations.

    • The thing is, we don’t need a tie to specific genes to invalidate an EP hypothesis. And that’s not a requirement for other behavioral-evolutionary sciences. So why should it be here? I agree that in all ideal worlds, such a requirement would be best, and I can see where you’re coming from, Larry (I hope you don’t mind the over-familiarity) given your focus of study, but is it really necessary? And wouldn’t it unnecessarily burden many growing and fascinating fields (EP/SB/others)? The time will come to make those connections, but it doesn’t appear to be possible or needed at the moment (although always worth a try).

      • The thing is, we don’t need a tie to specific genes to invalidate an EP hypothesis. And that’s not a requirement for other behavioral-evolutionary sciences. So why should it be here?

        Because the issue isn’t whether we can identify specific alleles, it’s whether there’s even a significant genetic component.

        What’s the point of speculating about adaptation if the trait is due to nurture, not nature?

        • bluharmony bluharmony

          I suppose that because without speculating (coming up with testable hypotheses) and falsifying, we’ll never know. And as Professor Wilkins pointed out in this installment on SB/EP, when it comes to complex traits that appear adaptive, the null hypothesis is no longer drift.

        • What’s the point of speculating about adaptation if the trait is due to nurture, not nature?

          Because “nurture” can be adaptive or maladaptive the same way “nature” does?

    • Also, in most EP studies I’ve read (granted that’s not many, but I’ve only been focusing on this subject since PZ’s posts, and Westlaw isn’t really giving me a whole lot to choose from), but potential non-genetic explanations are also often considered, no? Please correct me if I’m wrong. 🙂

  4. I really like the rigid poles and elastic connections analogy, John. Very clever, and I think it yields helpful intuition.

    • Oh, I meant to post this to my FB page. Will do.

  5. David Duffy David Duffy

    “Modularity, whether of genes or organs or neurological systems, is only ever a conceptual abstraction.”

    I’m not so sure of this. In terms of efficiency, homeostasis and robustness, we are generally better off if a system is modular and compartmentalised as far as possible. At the gene or gene network level, there can be functional modularity spreading over multiple cell type or tissues.

    In multitrait genetic analysis, a particular interest is in genetic covariances, the structure of which may allow one to deduce what
    the “real” traits are, in terms of fitness and selection.

    “- We often don’t know whether the trait in question even has a significant genetic component or whether it’s just nurture.”

    We can evaluate whether there is contemporary genetic variance for a given trait using various family based or genotyping-based designs. This is no guarantee of what went on in the past, though some EPers are working in modern hunter-gatherer groups eg the Hazda.

  6. Michael Fugate Michael Fugate

    This might be worth a look in the December issue of TREE:
    Social competence: an evolutionary approach
    Barbara Taborsky and Rui F. Oliveira

    ‘Social competence’ refers to the ability of an individual to optimise its social behaviour depending on available social information. Although such ability will enhance social interactions and thus raise Darwinian fitness, its evolutionary and ecological significance has been largely ignored. Social competence is based on behavioural flexibility. We propose that the study of social competence requires an integrative approach that aims to understand how the brain translates social information into flexible behavioural responses, how flexibility might be constrained by the developmental history of an individual or by trade-offs with other (ecological) competences, and how social plasticity feeds back on fitness. Finally we propose a hypothesis of how social competence can become a driver of social evolution.

  7. John Harshman John Harshman

    These days the consensus appears to be that species originate independently of natural selection processes, and selection changes the ecological adaptive features of the species rather than the isolation of species from other species.

    Not exactly. The consensus is that species originate mostly through selection acting differently on geographically isolated populations. Genetic isolation is a byproduct of selection rather than its target, but it’s still selection that results in that isolation. Drift can produce isolation too, but takes longer than selection. Have you read Coyne & Orr’s Speciation? That would bring you up to speed.

    For a trait to persist in a population (note, in a population, not a lineage of species over large periods) and to go to fixation if the population is of any size it is more often than not, much more often, due to selective pressures on those behaviours than to chance.

    This is true for any single trait, but not necessarily for traits as a whole. For example, a given SNP is much more likely to become fixed in the genome by selection than by drift. But the vast majority of SNPs that become fixed do so by drift. This apparent contradiction is resolved if we realize just how many SNPs there are and how few are under selection. In order to make your claim about behavior true, you must establish that a high percentage of them are under selection. If most behaviors are neutral, most of them are fated to become extinct but a few will become fixed. If the neutral behaviors are a high enough proportion of total behaviors, neutral fixations may outnumber the fixations due to selection, as is the case in the genome.

    • I think we are in violent agreement. In a throwaway comment like the one in the post, I can’t easily give all the nuances. I meant that the isolation of sexual species is not the result of selection for isolation.

      As to SNPs, I take the point.

  8. So the bottom line is that the only reason not to study potentially adaptive behaviors is that we may find answers we’d rather not. And that’s regardless of whether drift or selection is the default, which may depend on circumstance and other factors I’m not fully understanding.

    I’m still trying to get a better grasp on the single nucleotide polymorphism (SNP) contradiction mentioned above. It seems that some distinction should be made between traits that become fixed by selection as opposed to drift.

    • John Harshman John Harshman

      The big question there is how, operationally, to make that distinction. Assuming you have previously shown the trait to be strongly genetically influenced, how can you tell if it’s adaptive? And adaptive in what environment? Experimental manipulation is the common method, and with humans there are inconvenient ethical considerations. Field observation is another method, and that has its own difficulties.

      • I asked an Evolutionary Psychologist the same question, and got a long list of methods that are currently being used (all ethical). This problem has been and is being addressed, and methods exist to separate adaptation, byproduct, and drift. EP is presently taught in both introductory psychology classes and introductory evolution classes. Sometimes you have to set politics aside in favor of education. In fact, I would suggest that knowledge should inform politics, and not the other way around.

        • John Harshman John Harshman

          I would appreciate some insight into that list of methods.

      • Assuming you have previously shown the trait to be strongly genetically influenced, how can you tell if it’s adaptive?

        Actually, you don’t need to show the trait to be _strongly_ genetically influenced to study adaptation.

        Any level of genetic variation, strong or not, impacting a trait and impacting fitness can produce adaptations. Just imagine a weakly genetically influenced trait that is strongly selected. The genetic variation has great odds becoming fixed even if it is low. Don’t confuse genetic influence and selection strength!

        You also have to realise that natural selection is depleting variation (but so does drift for e.g.). So that adaptive traits are probably left with lower extant genetic variation than drifting ones.

        You can still study adaptation even if there’s no more genetic variation underlying your specific study trait. All you need is correlating variation in phenotypic range to some measure of fitness. If you have arguments about specific trait variation from the past (or can derive it in comparing closely related species with your study model), and your species express (or not) the trait so that it makes a good fit in your measured adaptive space, than you can reasonably assume it evolved adaptively (of course, you cannot rule out it did so by simply drifting to an adaptive spot, but we’re speaking science here, so that’s best guesses at natural history).

        But please understand that under adaptive scenario, you don’t expect much genetic variation left.

  9. I am glad to see you posting high-quality blog-posts once again. As someone who has been reading your blog since your earliest Seed blog days, there was a time (when you were having your difficulties) where I thought you’d disappear (like Gary Farber) through being over-whelmed by lousy circumstances.

    I’m so glad I kept you bookmarked during all this time. It’d have been a shame to mis-out on your elegant and insightful prose because I gave you up for dead.

    • Wilkins is great and his blog is superb. This site is a relatively new discovery for me. 🙂

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