Evolutionary Psychology (EP) is a discipline which purports to explain mental and psychological traits as adaptations—functional products of “natural selection”—which are genetically inherited/transmitted. Its main premises is that the human mind can be explained by evolution through natural selection; that the mind is “modular”—called the “massive modularity hypothesis” (see Pinker, 1997). EP purports that the mind is “a cluster of evolved information-processing mechanisms” with its main goal being “to characterize these Darwinian algorithms” (Sterelny and Griffiths, 1999: 336). The problem with EP, though, is that many of the “theories/hypotheses” are just speculation—what is termed “just-so stories” (Gould and Lewontin, 1979; Richardson, 2007; Nielsen, 2009; Fodor and Piattelli-Palmarini, 2010). In this article, I will discuss the massive modularity hypothesis, adaptationism, and the promises that EP makes as a whole.
The massive modularity hypothesis (MMH) proposes that the modules “for” mental processing evolved in response to “natural selection” (Samuels, 1998). To evolutionary psychologists, the mind is made up of different modules that were “selected for” different mental abilities. So, to evolutionary psychologists like Tooby and Cosmides, Pinker et al, much of human psychology is rooted in the Pleistocene (i.e., Tooby and Cosmides’ 5th Principle that “our modern skulls house a stone age mind“) . Evolutionary psychologists propose that the mind is made up of different, genetically influenced, modules that which were specifically selected as to help our ancestors solve domain-specific problems.
Two principle arguments exist for the MMH. Argument (1)—called the optimality argument—is:
- There are adaptive problems in every environment; different adaptive problems in different environments require different solutions, and different solutions can be implemented by functionally distinct modules.
- Adaptive problems are selective pressures; for each unique pressure faced in the original evolutionary environment (OEE), there is a unique module which was selected to solve those—and only those—specific adaptive problems.
- Selective mechanisms can produce highly specialized cognitive modules.
- Therefore, since different adaptive problems require different solutions and different solutions can be implemented by functionally distinct modules, then there must exist differing modules in the human mind which were selected for in virtue of their contribution to fitness.
Or the argument could be:
- Domain-specific processes exist
- These processes arose due to evolution
- Therefore these domain-specific processes that arose due to evolution have a genetic basis
Tooby and Cosmides claim that, distinct modules for certain adaptive problems in distinct environments are superior at solving different problems, rather than a general-purpose cognitive module. They argue that selection can produce different modules in the mind “for” different adaptive problems. Tooby and Cosmides put their argument in their own words as:
(1) As a rule, when two adaptive problems have solutions that are incompatible or simply different, a single solution will be inferior to two specialized solutions
(2) .. . domain-specific cognitive mechanisms . . . can be expected to systematically outperform (and hence preclude or replace) more general mechanisms
(3) Simply to survive and reproduce, our Pleistocene ancestors had to be good at solving an enormously broad array of adaptive problems—problems that would defeat any modern artificial intelligence system. A small sampling include foraging for food, navigating, selecting a mate, parenting, engaging in social exchange, dealing with aggressive threat, avoiding predators, avoiding pathogenic contamination, avoiding naturally occurring plant toxins, avoiding incest and so on
(4) [Therefore] The human mind can be expected to include a large number of distinct, domain-specific mechanisms (quoted from Samuels, 1998: 585-586)
Clearly, the assumption from Tooby and Cosmides is that specific modules for certain adaptive problems in the OEE are superior to general-purpose modules. Samuels (1998: 586) writes:
In the case of psychological traits, in order to use optimality considerations with any confidence one needs to know (a) what features were being optimized by the evolutionary process and (b) what range of phenotypes were available to natural selection. As a matter of fact, however, we have little knowledge about either of these matters.
The key point of the MMH is that, according to Tooby and Cosmides, we would expect that the mind consists of different modules which are “designed” to solve domain-specific problems. If we know what type of adaptive situations happened to our ancestors then we should be able to construct the evolution of a trait by knowing its current functional use and “working backwards”—what is termed “reverse engineering”—inferring “function” from “cause” (see Richardson, 2007: chapter 2); inferring effect from relevant causes (see Richardson, 2007: chapter 3) and disentangling historical ancestry from history and structure (see Richardson, 2007: chapter 4).
As for their second argument:
- It is impossible for human psychology—that contains nothing but general-purpose mechanisms—to have evolved since such a system cannot be adaptive.
- Such a system cannot possibly have solved the adaptive problems faced by our ancestors in the evolutionary past.
- Therefore, the mind cannot possibly have evolved general-purpose mechanisms and had to have evolved different mental modules in order to carry out different tasks.
They defend the argument by stating that the domain-dependence of different errors is a cause of the evolution of different modules of the mind; that information for crucial adaptive behavior cannot be learned by using only domain-specific systems; and that many adaptive problems are highly complex and unlikely to have been solved by general-purpose modules. Therefore, the mind must be modular since this can account for domain-specific problems—while, according to Tooby and Cosmides, general-purposed modules cannot. The argument, though, fails to provide us with any reason to accept the claim that the mind is made up of mostly—or is all made up of—Darwinian modules which were kept around since they were targets of selection.
Clearly, evidence for the modularity of mind is lacking—as is the evidence that reverse engineering “works” for the purpose intended.
Lloyd (1999: 224) writes that:
Given these difficulties – well-known especially since Konrad Lorenz and Nico Tinbergen’s pioneering experiments on animal behavior – it is not scientifically acceptable within evolutionary biology to conclude that, because a given pattern of responses contributes to evolutionary success, then there is some ‘organ’ (or part of the brain) producing such a pattern, that is therefore an adaptation (see Williams 1966). This is because the ‘organ’ or ‘module’ may not actually exist as a biologically real trait, and even if it does, its current function may or may not be the same as the past function(s).
Sterelny and Griffiths (1999: 342) write that “… evolutionary psychology has bought into an oversimplified view of the relationship between an evolving population and its environment, and has prematurely accepted a modular conception of the mind.”
Tooby and Cosmides (1992) coined the phrase “Standard Social Science Model” (SSSM) in order to differentiate their EP model (the “integrated causal model”; ICM) from the SSSM. According to Tooby and Cosmides (1992), the basis of the SSSM is to employ complete general-purpose cognitive modules and to deny any type of nativist modules whatsoever. Therefore, according to Tooby and Cosmides’ characterization of their so-called “opposition”, interesting differences between groups—and, of course, individuals—are due completely to cultural conditioning with absolutely no nativist elements since there are only general-purpose modules. Differences between individuals, according to the SSSM, are cultural products—differences in socialization cause individual differences.
Richardson (2007:179) writes:
Tooby and Cosmides’ portrayal [of the SSSM] is very effective. It is also a piece of sophistry, offering a false dichotomy between a manifestly untenable view and their own. The alternative is one that sees no differences between individuals and no biological contribution to individual or social development. I think no serious figure embraces that view, since, perhaps, John Watson in the early twentieth century.
Tooby and Cosmides also say that “There is no small irony in the fact that [the[ Standard Social Science MOdel’s hostility to adaptationist approaches is often justified through the accusation that adaptationist approaches purportedly attribute important differences between individuals, races and classes to genetic differences. In actuality, adaptationist approaches offer the explanation for why the psychic unity of humankind is genuine and not just an ideological fiction” (1992, 79).
Furthermore, David Buss claims that “Natural selection is the only prospect for explaining human nature” (Richardson, 2007: 182). (Whatever “human nature” is. See Nagel’s 2012 Mind and Cosmos for arguments that the mind cannot possibly have been naturally selected since evolutionary biology is a physical theory and Fodor and Pitatelli-Palmarini’s 2010 book What Darwin Got Wrong for the argument against natural selection as an explanatory mechanism in regard to trait fixation.)
Problems with the adaptationist paradigm
Adaptationism is a research programme in which, according to the Stanford Encyclopedia of Philosophy, ““adaptationists” view natural selection among individuals within a population as the only important cause of the evolution of a trait; they also typically believe that the construction of explanations based solely on natural selection to be the most fruitful way of making progress in evolutionary biology and that this endeavor addresses the most important goal of evolutionary biology, which is to understand the evolution of adaptations.”
Though numerous problems exist with this programme, not least the claim that most—or all—important phenotypic traits are the product of evolution by natural selection. In their book Sex and Death: An Introduction to Philosophy of Biology, Sterelny and Griffiths (1999: 351) write:
Adaptive explanation is an inference from the current phenotype of an organism to the problems that organism faced in its evolutionary past. Obviously, that inference will be problematic if we do not have an accurate description of the current phenotype and its adaptive significance—of the solution that evolution actually produced. The inference from current adaptive importance to adaptation is problematic enough even when the adaptive and phenotypic claims on which it is based are uncontroversial (13.1). The inference is still more problematic when the nature of the phenotype and its adaptive importance are yet to be established.
This is not the main problem with the paradigm, though. The main problem is that all of these theories/hypotheses are “just-so stories”—“… an adaptive scenario, a hypothesis about what a trait’s selective history might have been and hence what its function may be” (Sterelny and Griffiths, 1999: 61). I’d also add that just-so stories are stories that cannot be independently verified of the data that they purport to explain—that is, there is no observation that can disconfirm the adaptationist “hypothesis”, and the only data that “proves” the hypothesis is the data it purports to explain. EP hypotheses are not testable. Therefore EP hypotheses are just-so stories.
Sterelny and Griffiths (1999: 338) “… agree with the central idea of evolutionary psychology, namely, that we should look for the effects of natural selection on the psychological mechanisms that explain our behaviors, rather than on those behaviors themselves.” I disagree, since it is not possible that “psychological mechanisms” can be selected.
What is the relationship between environment and adaptation? First, we need to think of some “problems” that exist in the environment. One example is mate choice: Should one be faithful to their partner? When should one abandon their old partner? When should they help their kin find partners? When and how should one punish infidelity? This problem, pretty obviously, is evidence against the idea that adaptations are explained by the problem to which the adapted trait is the solution (see David Buller’s 2005 book Adapting Minds for strong critiques against “reverse engineering”). If—and only if—a single cognitive device exists that guides a creature’s behavior with respect to the issues of mate choice, the issue is then a single-domain, not multi-domain, problem, while there are different aspects of the same problem (see the questions above). The existence of said module explains why we think of mate choice as a single problem.
Sterelny and Griffiths (1999: 342) are hopeful in EP’s quest to discover our shared “human nature”, “But both the objective and subjective obstacles to carrying out this program remain serious.” The adaptationist programme, however, is unfalsifiable. “Particular adaptive stories can be tested, as we discuss below, but Gould and Lewontin argue that this does not test the idea of adaptationism itself. Whenever a particular adaptive story is discredited, the adaptationist makes up a new story, or just promises to look for one. The possibility that the trait is not an adaptation is never considered” (Sterelny and Griffiths, 1999: 237).
Adaptationist explanations (EP is—mostly—nothing but adaptationist explanation) are not scientific since they cannot be falsified—EP hypotheses are not falsifiable, nor do they generate testable predictions. They only explain the data it purports to explain—meaning that all EP adaptationist explanations are just-so stories. (Also see Kaplan, 2002 for arguments against the adaptationist paradigm.)
Even those who are sympathetic to the EP research programme, rightly, point out the glaring flaws in the programme. These flaws—in my opinion—cannot be overcome. EP will always be “plausible and speculatuve ” just-so stories that purport to explain the evolution of what, supposedly, are traits that were “selected for” in virtue of their contribution to fitness in the OEE. However, we do not (and cannot) know what the OEE was like—we would need a time machine. It is not possible for us to know the selective pressures that occurred on our ancestors in the OEE. We do know that increased reproductive efficiency in the current-day is not evidence that said trait was adaptive and selected in the OEE.
The mind is not modular; Tooby and Cosmides proposed a false dichotomy (their ICM vs SSSM) which is not valid (no one is a “blank slatist”, whatever that is); and the adaptationist paradigm is nothing but speculative just-so stories.
- For EP to be a valid research programme, EP hypotheses must generate testable, falsifiable predictions.
- EP cannot generate testable, falsifiable predictions (the hypotheses are inherently ad hoc).
- Therefore, EP is not a valid research programme.
There is no reason at all to accept any just-so story since these adaptive explanations cannot produce evidence that the trait was not a byproduct, due to genetic drift etc. Therefore EP is not a scientific enterprise; it only tells “plausible”, speculative stories just-so stories “… I view evolutionary psychology as more speculation than science. The conclusion I urge is, accordingly, skeptical. Speculation is just that: speculation. We should regard it as such. Evolutionary psychology as currently practiced is often speculation disguised as results. We should regard it as such” (Richardson, 2007: 25). This is the view that should be accepted in the mainstream, since there can be no evidence for the speculative stories of EP.