Evolutionary Psychology

In its broad sense, the term "evolutionary psychology" stands for any
attempt to adopt an evolutionary perspective on human behavior by
supplementing psychology with the central tenets of evolutionary
biology. The underlying idea is that since our mind is the way it is
at least in part because of our evolutionary past, evolutionary theory
can aid our understanding not only of the human body, but also of the
human mind. In this broad sense, evolutionary psychology is a general
field of inquiry that includes such diverse approaches as human
behavioral ecology, memetics, dual-inheritance theory, and
Evolutionary Psychology in the narrow sense.

The latter is a narrowly circumscribed adaptationist research program
which regards the human mind as an integrated collection of cognitive
mechanisms that guide our behavior and form our universal human
nature. These cognitive mechanisms are supposed to be adaptations—the
result of evolution by natural selection, that is, heritable variation
in fitness. Adaptations are traits present today because in the past
they helped our ancestors to solve recurrent adaptive problems. In
particular, Evolutionary Psychology is interested in those adaptations
that have evolved in response to characteristically human adaptive
problems that have shaped our ancestors' lifestyle as hunter-gatherers
during our evolutionary past in the Pleistocence, like choosing and
securing a mate, recognizing emotional expressions, acquiring a
language, distinguishing kin from non-kin, detecting cheaters or
remembering the location of edible plants. The purpose of Evolutionary
Psychology is to discover and explain these cognitive mechanisms that
guide current human behavior because they have been selected for as
solutions to the recurrent adaptive problems prevalent in the
evolutionary environment of our ancestors.

Evolutionary Psychology thus rests on a couple of key arguments and
ideas: (1) The claim that the cognitive mechanisms that are underlying
our behavior are adaptations. (2) The idea that they cannot be studied
directly, for example, through observation of the brain or our overt
behavior, but have to be discovered by means of a method known as
"functional analysis," where one starts with hypotheses about the
adaptive problems faced by our ancestors, and then tries to infer the
cognitive adaptations that must have evolved to solve them. (3) The
claim that these cognitive mechanisms are adaptations not for solving
problems prevalent in our modern environment, but for solving
recurrent adaptive problems in the evolutionary environment of our
ancestors. (4) The idea that our mind is a complex set of such
cognitive mechanisms, or domain-specific modules. (5) The claim that
these modules define who we are, in the sense that they define our
universal human nature and ultimately trump any individual, cultural
or societal differences.

1. Historic and Systematic Roots

Modern Evolutionary Psychology has its roots in the late 1980s and
early 1990s, when psychologist Leda Cosmides and anthropologist John
Tooby from Harvard joined the anthropologist Donald Symons at The
University of California, Santa Barbara (UCSB) where they currently
co-direct the Center for Evolutionary Psychology. It gained wide
attention in 1992 with the publication of the landmark volume The
Adapted Mind by Jerome Barkow, Leda Cosmides and John Tooby, and since
then numerous textbooks (for example, Buss 1999) and popular
presentations (for example, Pinker 1997, 2002; Wright 1994) have
appeared. These days, Evolutionary Psychology is a powerful research
program that has generated some interesting research, but it has also
sparked a heated debate about its aspirations and limitations (see,
for example, Rose and Rose 2000).

Evolutionary Psychology is effectively a theory about How the Mind
Works (Pinker 1997). The human mind is not an all-purpose problem
solver relying on a limited number of general principles that are
universally applied to all problems—a view that dominated early
artificial intelligence (AI) and behaviorism (for example, Skinner
1938, 1957). (For the idea of an all-purpose problem solver see, for
example, Newell and Simon 1972; for some of the earliest AI work
related to this idea see, for example, Newell and Simon 1961, Newell
et al. 1958.) Rather, the human mind is a collection of independent,
task-specific cognitive mechanisms, a collection of instincts adapted
for solving evolutionary significant problems. The human mind is sort
of a Swiss Army knife (Pinker 1994). This conception of the mind is
based on three important ideas adopted from other disciplines
(Cosmides and Tooby 2003, 54; Samuels 1998, 577): the computational
model of the mind, the assumption of modularity, and the thesis of
adaptationism.

a. The Computational Model of the Mind

Following the development of modern logic (Boole 1847; Frege 1879) and
the formalization of the notion of computation (Turing 1936), early AI
construed logical operations as mechanically executable information
processing routines. Eventually, this led to the idea that mental
processes (for example, reasoning) and mental states (for example,
beliefs and desires) may themselves also be analyzable in purely
syntactic terms. The "Computational Theory of Mind," developed by
philosophers like Hilary Putnam (1963) and Jerry Fodor (1975, 1981),
for instance, conceives of mental states as relations between a
thinker and symbolic representations of the content of the states, and
of mental processes as formal operations on the syntactic features of
those representations.

Evolutionary Psychology endorses the computational model of the mind
as an information processing system or a formal symbol manipulator and
thus treats the mind as a collection of "computational machines"
(Cosmides and Tooby 2003, 54) or "information-processing mechanisms"
(Tooby and Cosmides 1990a, 21) that receive input from the environment
and produce behavior or physiological changes as output. To this, it
adds an evolutionary perspective: "The evolutionary function of the
human brain is to process information in ways that lead to adaptive
behavior; the mind is a description of the operation of a brain that
maps informational input onto behavioral output" (Cosmides and Tooby
1987, 282). The brain is thus not just like a computer. "It is a
computer—that is, a physical system that was designed to process
information" (Tooby and Cosmides 2005, 16; italics added).

The Computational Model of the Mind: The human mind is an
information processing system, physically realized in the brain, and
can be described at a computational level as a device whose
evolutionary function is to process information by mapping
informational input onto behavioral output.

b. The Modularity of Mind

Early attempts at simulating human intelligence revealed that
artificial cognitive systems that are not already equipped with a fair
amount of "innate knowledge" about a particular problem domain are
unable to solve even the easiest problems (see, for example, the idea
of "scripts" in Schank and Abelson 1977). In the 1970s and 1980s, the
work of scientists like Noam Chomsky, Jerry Fodor, or David Marr
further undermined the idea of the mind as a "blank slate" which
acquires knowledge about the world by means of only a couple of
general learning mechanisms. Their findings suggested instead that the
mind incorporates a number of cognitive subsystems that are triggered
only by a certain kind of input. While Marr (1982) was working on the
neuroscience of vision, Chomsky famously criticized the behaviorist
idea that language acquisition is just an ordinary kind of learning
that follows the stimulus-response model by proving the intractability
of some learning algorithms (see, for example, his 1959 review of
Skinner's Verbal Behavior or Chomsky 1957; for a later statement of
similar ideas see Chomsky 1975). According to his "Poverty of the
Stimulus" argument, a child cannot learn her first language through
observation because the available stimuli (that is, the utterances of
adult speakers) neither enable her to produce grammatically correct
nor prevent her from producing grammatically incorrect sentences.
Instead, Chomsky argued, we possess a "language acquisition device"
which, rather than extracting all information from the world through
some general mechanism, comes already equipped with a certain amount
of "innate knowledge." Just as our body contains a number of innate,
genetically predisposed organs that serve a specific function, our
mind also contains a number of information processing systems (like
the language acquisition device), so called mental organs or modules
in Fodor's (1983) terminology, that are designed to perform a
particular cognitive function.

The model of the mind as a general learning mechanism that is
indiscriminately applied to any problem domain was also disconfirmed
in other areas of cognitive science. Garcia and Koelling (1966) showed
that while rats can learn some associations by means of
stimulus-response mechanisms, others, albeit structurally similar,
cannot be learned at all, or only much slower: rats that are given
food that makes them nauseous subsequently avoid that kind of food,
but they are unable to learn an association between a sound or a light
and feeling nauseous. Galef (1990) demonstrated that rats readily eat
a new kind of food if they smell it at another rat's mouth, but not if
they smell it at another part of the body. Mineka and Cook (1988)
showed that a laboratory raised monkey that initially did not show
fear of snakes started to do so once he observed another monkey
exhibiting fear of snakes; yet, he didn't start to show fear of
flowers when observing the other doing so. Comparable "learning
biases" have been found for humans in various areas (for example, Cook
et al. 1986; Marks and Nesse 1994; Seligman and Hagar 1972).

Evolutionary Psychologists conclude that the assumption that the human
mind is composed mainly of a few content-free cognitive processes that
are "thought to govern how one acquires a language and a gender
identity, an aversion to incest and an appreciation for vistas, a
desire for friends and a fear of spiders—indeed, nearly every thought
and feeling of which humans are capable" (Ermer et al. 2007, 155) is
inadequate. Such mechanisms would be "limited to knowing what can be
validly derived by general processes from perceptual information"
(Cosmides and Tooby 1994, 92) and thus incapable of efficiently
solving adaptive problems (see section 2d). Instead, Evolutionary
Psychologists claim, "our cognitive architecture resembles a
confederation of hundreds or thousands of functionally dedicated
computers" (Tooby and Cosmides 1995, xiii), the so-called "modules":

Modularity: The mind consists of a (possibly large) number of
domain-specific, innately specified cognitive subsystems, called
"modules."

c. Adaptationism

Since cognitive mechanisms are not directly observable, studying them
requires some indirect way of discovering them (see section 2b).
Evolutionary Psychologists adopt the kind of adaptationist reasoning
well known from evolutionary biology that also characterizes many
works in sociobiology (Wilson 1975). Ever since Charles Darwin
(1859/1964) proposed his theory of evolution by natural selection,
evolutionary biologists quite successfully offer adaptationist
explanations of physiological features of living things that explain
the presence of a trait by claiming that it is an adaptation, that is,
a trait current organisms possess because it enhanced their ancestors'
fitness. During the 1970s, sociobiologists argued that "social
behaviors [too] are shaped by natural selection" (Lumsden and Wilson
1981, 99; for the original manifesto of sociobiology see Wilson 1975)
and started to seek adaptationist explanations for cognitive,
cultural, and social traits, like the ability to behave
altruistically, different mating preferences in males and females, or
the frequently observed parent-offspring conflicts.

Evolutionary Psychologists have inherited sociobiology's adaptationist
program: "The core idea … is that many psychological characteristics
are adaptations—just as many physical characteristics are—and that the
principles of evolutionary biology that are used to explain our bodies
are equally applicable to our minds" (Durrant and Ellis 2003, 5). Our
mind, they argue, is a complex, functionally integrated collection of
cognitive mechanisms, and since the only known natural process that
can bring about such functional complexity is evolution by natural
selection (Cosmides and Tooby 1991, 493; Symons 1987, 126; Tooby and
Cosmides 1990b, 382), these cognitive mechanisms are likely to be
adaptations to the adaptive problems of our ancestors. This,
Evolutionary Psychologists hold, intimately links psychology with
evolutionary theory: "Because the architecture of the human mind
acquired its functional organization through the evolutionary process,
theories of adaptive function are the logical foundation on which to
build theories of the design of cognitive mechanisms" (Ermer et al.
2007, 153–4). While evolutionary theory is used to describe the
relevant ancestral problems and to make educated guesses about the
information processing cognitive mechanisms that have been shaped by
natural selection in response, the task of psychology is to establish
that current humans actually possess these mechanisms (see section
2b).

Adaptationism: The human mind, like any other complex feature, was
shaped by a process of evolution through natural selection. Its
subsystems, the modules, are adaptations for solving recurrent
information processing problems that arose in our ancestors'
evolutionary environment.

2. Key Concepts and Arguments

According to Evolutionary Psychology, the human mind is a set of
cognitive adaptations designed by natural selection. Since such design
takes time, the adaptive problems that shaped our mind are not the
ones we know from our life as industrialists during the past 200
years, or from our life as agriculturalists during the past 10,000
years, but those characteristic of our past life as hunter-gatherers.
Since these problems varied considerably, the human mind contains many
problem-specific adaptations. The task of Evolutionary Psychology is
to discover these modules by means of what is called a "functional
analysis," where one starts with hypotheses about the adaptive
problems faced by our ancestors, and then tries to infer the cognitive
adaptations that must have evolved to solve them.

This theoretical framework of Evolutionary Psychology centers on a
couple of key ideas which will be explained in this section: (1) The
cognitive mechanisms that underlie our behavior are adaptations. (2)
They have to be discovered by means of functional analysis. (3) They
are adaptations for solving recurrent adaptive problems in the
evolutionary environment of our ancestors. (4) Our mind is a complex
set of such mechanisms, or domain-specific modules. (5) These modules
define our universal human nature.

a. Adaptation and Adaptivity

That our evolutionary history influenced not only our bodies, but also
our brains, and thus our minds, is not very controversial. But how
exactly has evolution affected the way we are, mind-wise? How exactly
can evolutionary theory elucidate the structure and function of the
human mind?

It may seem that "behavioral traits are like any other class of
characters" (Futuyama 1998, 579), so that they can be subject to
natural selection in the same way as physiological traits. In that
case, an evolutionary study of human behavior could then proceed by
studying behavioral variants and see which of them are adaptive and
which selectively neutral or detrimental. However, since natural
selection is heritable variation in fitness, it can act only on
entities that are transmitted between generations, and behavior as
such is not directly transmitted between generations, but only via the
genes that code for the proximal cognitive mechanisms that trigger it.
Hence, "[t]o speak of natural selection as selecting for 'behaviors'
is a convenient shorthand, but it is misleading usage. … Natural
selection cannot select for behavior per se; it can only select for
mechanisms that produce behavior" (Cosmides and Tooby 1987, 281).

Hence, an evolutionary approach to human psychology must proceed by
studying the cognitive mechanisms that underlie our behavior: "In the
rush to apply evolutionary insights to a science of human behavior,
many researchers have made a conceptual 'wrong turn,' … [which] has
consisted of attempting to apply evolutionary theory directly to the
level of manifest behavior, rather than using it as a heuristic guide
for the discovery of innate psychological mechanisms" (Cosmides and
Tooby 1987, 278–9). By sharply distinguishing between adaptive
behavior and the cognitive mechanisms that are adaptations for
producing adaptive behavior, Evolutionary Psychologists provide "the
missing link between evolutionary theory and manifest behavior" (Tooby
and Cosmides 1989, 37). [The drawback is that things become more
complicated since "it is less easy to sustain claims that a trait is a
product of natural selection than claims that it confers reproductive
benefits on individuals in contemporary populations" (Caro and
Borgerhoff Mulder 1987, 66). Section 2b shows how Evolutionary
Psychologists try to cope with this difficulty, and section 5a
discusses a version of evolutionary psychology that focuses on
adaptive behavior.]

We quite often do things detrimental to survival and reproduction (we
use contraceptives, consume unhealthy doses of fatty food, and blow
ourselves up in the middle of crowded market places). We also
willfully refrain from doing things that would be conducive to
survival (buy some healthy food, exercise) or boost our potential for
reproduction (donate our sperm or eggs to cryobanks). If Evolutionary
Psychology is right that our mind contains cognitive mechanisms that
are adaptations for producing adaptive behavior, then why are we
behaving maladaptively so often?

The claim that the brain is an adaptation for producing adaptive
behavior does not entail that it is currently producing adaptive
behavior. Adaptations are traits that are present today because of the
selective advantage they offered in the past, and the past environment
arguably differed notably from the current one. The modern metropolis
in which we live in unprecedented large groups, consume fast food and
use contraceptives is not even 100 years old, and even agriculture
arose only some 10,000 years ago. Compared to this, our ancestors
spent an unimaginably long time in Pleistocene conditions (roughly,
the period spanning 1.8 million years ago to 10,000 years ago) living
in small nomadic hunter-gatherer bands. The cognitive mechanisms
produced by natural selection are adaptations for producing adaptive
behavior in these circumstances, not for playing chess, passing logic
exams, navigating through lower Manhattan, or keeping ideal weight in
an environment full of fast food restaurants. [Which is why we are so
bad at these things: "it is highly unlikely that the cognitive
architecture of the human mind includes procedures that are dedicated
to solving any of these problems: The ability to solve them would not
have enhanced the survival or reproduction of the average Pleistocene
hunter-gatherer" and hence "the performance of modern humans on such
tasks is generally poor and uneven" (Cosmides and Tooby 1994, 95).]

Among the day-to-day problems of our ancestors that shaped the human
mind are: "giving birth, winning social support from band members,
remembering the locations of edible plants, hitting game animals with
projectiles, …, recognizing emotional expressions, protecting family
members, maintaining mating relationships, …, assessing the character
of self and others, causing impregnation, acquiring language,
maintaining friendships, thwarting antagonists, and so on" (Cosmides
and Tooby 2003, 59). In these areas, we still behave the way we do
because our behavior is guided by cognitive mechanisms that have been
selected for because they produced behavior that was adaptive in our
ancestors' evolutionary environment. As Evolutionary Psychologists
colorfully put it: "Our modern skulls house a Stone Age mind"
(Cosmides and Tooby 1997, 85).

It is thus crucial to distinguish between a trait's being an
adaptation and its being adaptive. A trait is an adaptation if it was
"designed" by natural selection to solve the specific problems posed
by the regularities of the physical, chemical, ecological,
informational, and social environments encountered by the ancestors of
a species during the course of its evolution" (Tooby and Cosmides
1990b, 383), while a trait is adaptive if it currently enhances its
bearer's fitness. Since the environment in which a trait was selected
for may differ from the current one, "[t]he hypothesis that a trait is
an adaptation does not imply that the trait is currently adaptive"
(Symons 1990, 430). But if cognitive adaptations can neither be
discovered in the brain, nor by observing current human behavior, how
can they be studied?

b. Functional Analysis

Verifying the claim that a trait is an adaptation is difficult because
this is essentially a historical claim. A trait is an adaptation
because it was adaptive in the past, and it is unclear what the past
was like, let alone what would have been adaptive under past
conditions. According to Evolutionary Psychology, however, it is
possible to verify adaptationist claims:

Researchers can identify an aspect of an organism's physical,
developmental, or psychological structure … as an adaptation by
showing that (1) it has many design features that are improbably well
suited to solving an ancestral adaptive problem, (2) these phenotypic
properties are unlikely to have arisen by chance alone, and (3) they
are not better explained as the by-product of mechanisms designed to
solve some alternative adaptive problem or some more inclusive class
of adaptive problem. Finding that a reliably developing feature of the
species' architecture solves an adaptive problem with reliability,
precision, efficiency, and economy is prima facie evidence that an
adaptation has been located. (Tooby and Cosmides 2005, 28)

What Tooby and Cosmides suggest is a procedure known as functional
analysis. One uses evolutionary reasoning to identify the adaptive
problems our ancestors presumably awaited in their evolutionary
environment, infers from this the cognitive mechanisms that one thinks
must have evolved to solve these problems, conducts psychological
experiments to show that they are actually found in current human
beings, and rules out alternative explanations.

A bit more precisely, identifying adaptations by means of functional
analysis proceeds in six steps (Tooby and Cosmides 1989, 40–1):

Step 1 uses evolutionary considerations to formulate a model of the
past adaptive problems the human mind had to solve.

Step 2 generates hypotheses about exactly how these problems would
have manifested themselves under the selection pressures present in
the evolutionary environment of our ancestors.

Step 3 formulates a "computational theory" that specifies "a catalog
of the specific information processing problems" (Cosmides and Tooby
1987, 289) that had to be solved to overcome the adaptive problems
identified in step 2.

Step 4 uses the computational theory "as a heuristic for generating
testable hypotheses about the structure of the cognitive programs that
solve the adaptive problems in question" (Cosmides and Tooby 1987,
302).

Step 5 rules out alternative accounts of the cognitive mechanisms in
question that do not treat them as the result of evolution by natural
selection.

Step 6 tests the adaptationist hypotheses by checking whether modern
Homo sapiens indeed possess the cognitive mechanisms postulated in
step 4. If this test is successful, Evolutionary Psychologists
contend, it is quite likely that the cognitive mechanisms are indeed
adaptations for solving the problems identified in step 1. (For
examples of empirical research that, by and large, follow this
theoretical framework, see section 3.)

(One may add a seventh step which tries to discover the neural basis
of the cognitive mechanisms, so that eventually theories of adaptive
problems guide the search for the cognitive mechanisms that solve
them, while knowing what cognitive mechanisms exist in turn guides the
search for their neural basis.)

The procedure of functional analysis shows what sort of evidence would
support the claim that a cognitive mechanism is an adaptation for
solving a given adaptive problem. However, since functional analysis
itself relies on hypotheses about the adaptive problems prevalent in
our ancestors' past, the obvious question is: How can we today know
with any certainty which adaptive problems our ancestors faced?

c. The Environment of Evolutionary Adaptedness

Since the "description of ancestral conditions is one indispensable
aspect of characterizing an adaptation" (Tooby and Cosmides 1990b,
387), discovering the mind's modules requires knowing what exactly the
environment that Bowlby (1969) calls the environment of evolutionary
adaptedness (EEA) looked like. The human EEA consists in the set of
environmental conditions encountered by human populations during the
Pleistocene (from 1.8 million years ago to 10,000 years ago), when
early hominids lived on the savannahs of eastern Africa as
hunter-gatherers. Yet, the EEA "is not a place or a habitat, or even a
time period. Rather, it is a statistical composite of the
adaptation-relevant properties of the ancestral environments
encountered by members of ancestral populations, weighted by their
frequency and fitness consequences" (Tooby and Cosmides 1990b, 386–7).
More specifically, it is a "composite of environmental properties of
the most recent segment of a species' evolution that encompasses the
period during which its modern collection of adaptations assumed their
present form" (Tooby and Cosmides 1990b, 388). Importantly, "different
adaptations will have different EEAs. Some, like language, are firmly
anchored in approximately the last two million years; others, such as
infant attachment, reflect a much lengthier evolutionary history"
(Durrant and Ellis 2003, 10). Speaking about the EEA is thus at least
misleading, since strictly speaking one has to distinguish between the
EEA of a species and the EEA of particular cognitive adaptations.

There are two crucial questions with regard to the EEA: First, why
suppose that our cognitive mechanisms, even if they are adaptations,
are adaptations to exactly the problems faced by our ancestors in the
EEA? Second, how can we today determine the EEA of a particular
adaptation in enough detail?

Evolutionary Psychologists offer two related arguments in response to
the first question. The first draws attention to the large amount of
time our ancestors spent in Pleistocene conditions compared to the
brief stretch of time that has passed since the advent of agriculture
or industrialization: "Our species spent over 99% of its evolutionary
history as hunter-gatherers in Pleistocene environments. Human
psychological mechanisms should be adapted to those environments, not
necessarily to the twentieth-century industrialized world" (Cosmides
and Tooby 1987, 280). The second argument maintains that since natural
selection is a slow process, there just have not been enough
generations for it to design new cognitive mechanisms that are
well-adapted to our post-agricultural industrial life: "It is no more
plausible to believe that whole new mental organs could evolve since
the Pleistocene … than it is to believe that whole new physical organs
such as eyes would evolve over brief spans. … [and] major and
intricate changes in innately specified information-processing
procedures present in human psychological mechanisms do not seem
likely to have taken place over brief spans of historical time" (Tooby
and Cosmides 1989, 34).

Both arguments seem to suffer from the same difficulty. The 10,000
years that have passed since the Pleistocene correspond to roughly 400
generations, and if the selection pressure and the heritability
(roughly, a measure of the response to selection) are high enough,
quite a lot can happen in 400 generations. In particular, no one needs
to hold that "whole new mental organs could evolve since the
Pleistocene." In order to undermine the claim that we are walking
fossils with Stone Age minds in our heads, it is sufficient to show
that significant changes can occur within 400 generations. The same
observation threatens the first argument: How much time our ancestors
spent in one environment as compared to another is completely
irrelevant, if the selection pressures in one differ radically from
those in the other.

In response to the second question, Evolutionary Psychologists point
out that, first, we can be relatively sure that the physical
conditions were comparable to the ones today—"an enormous number of
factors, from the properties of light to chemical laws to the
existence of parasites, have stably endured" (Tooby and Cosmides
1990b, 390)—and, second, we can be relatively certain on
paleontological grounds that a great deal of our ancestors spend a
great deal of their time on African savannahs as hunter-gatherers.
Yet, since it is in response to the social problems faced by our
ancestors that our cognitive adaptations are said to have evolved,
what matters is not so much the physical environment (which may have
stayed constant, by and large) but the social environment, and the
question is what we can know with any certainty about the social life
of our ancestors, given that social traits do not fossilize.

Evolutionary Psychologists contend that with regard to the social
environment little has changed, too: our ancestors arguably had to
attract and retain mates, provide care for their children, understand
the intentions and emotions of those with whom they engaged in social
exchange, and so forth, just as we do. However, such general knowledge
about the EEA seems to be of little use, for discovering cognitive
adaptations requires formulating a computational theory that provides
"a catalog of the specific information processing problems" (Cosmides
and Tooby 1987, 289; italics added), and that goes significantly
beyond being told that our ancestors had to find mates, care for
children, find food and so forth (for more on this see section 4c).

d. Domain-specificity and Modularity

Empiricism in philosophy, behaviorism in psychology and the rules and
representation approach to artificial cognitive systems characteristic
of GOFAI ("good old fashioned artificial intelligence"), roughly
speaking, shared the belief that our mind contains only a few
domain-general cognitive mechanisms that account for everything we can
learn, be it speaking and understanding a language, solving algebra
equations, playing chess or driving a bike. In contrast, Evolutionary
Psychologists insist that "[f]rom an evolutionary perspective, the
human cognitive architecture is far more likely to resemble a
confederation of hundreds or thousands of functionally dedicated
computers … than it is to resemble a single general purpose computer
equipped with a small number of domain-general procedures" (Tooby and
Cosmides 2000, 1171).

Evolutionary Psychologists have advanced three arguments for this
modularity, or massive modularity, hypothesis. In short, a
domain-general psychological architecture cannot guide behavior in
ways that promote fitness for at least three related reasons:

1. What counts as fit behavior differs from domain to domain, so
there is no domain-general criterion of success or failure that
correlates with fitness.
2. Adaptive courses of action can be neither deduced nor learned by
general criteria, because they depend on statistical relationships
between features of the environment, behavior, and fitness that emerge
over many generations and are, therefore, not observable during a
single lifetime.
3. Combinatorial explosion paralyzes any truly domain-general
system when encountering real-world complexity. (Cosmides and Tooby
1994, 91)

Simply put, the idea behind the first argument is that "[t]here is no
such thing as a 'general problem solver' because there is no such
thing as a general problem" (Symons 1992, 142). Our ancestors faced a
host of different adaptive problems, and "different adaptive problems
frequently have different optimal solutions" (Cosmides and Tooby 1991,
500): what counts as a successful solution to one, say choosing a
mate, arguably differs from what counts as a successful solution to
another, say choosing nutritious food. Hence, there is no
domain-general criterion of success or failure: "A woman who used the
same taste preference mechanisms in choosing a mate that she used to
choose nutritious foods would choose a very strange mate indeed, and
such a design would rapidly select itself out" (Cosmides and Tooby
1994, 90). Hence, because different solutions can be implemented only
by different, functionally distinct mechanisms, there must be as many
domain-specific subsystems as there are domains in which the
definitions of successful behavior differ. "The human mind … is
composed of many different programs for the same reason that a
carpenter's toolbox contains many different tools: Different problems
require different solutions" (Tooby and Cosmides 2000, 1168). In
response to this argument, the critics have pointed out that there is
no reason why a cognitive system that relies on a few domain-general
mechanisms that are fed with innate domain-specific information should
not be as good as a modular cognitive architecture (see, for example,
Samuels 1998, 587).

According to the second argument, a domain general decision rule such
as "Do that which maximizes your inclusive fitness" cannot efficiently
guide behavior because whether or not a behavior is fitness enhancing
is something an individual often cannot find out within its own
lifetime, given that the fitness impact of a design feature relative
to alternative designs "is inherently unobservable at the time the
design alternative actually impacts the world, and therefore cannot
function as a cue for a decision rule" (Tooby and Cosmides 1990b,
417). As Buss has put it: "the relevant fitness information only
becomes known generations later and hence is not accessible to
individual actors" (Buss 1995, 10). For instance, whether one should
prefer fatty food over vegetables, or whether one should decide to
have children with potential partner A or with rival B are behavioral
decisions whose impact on one's fitness clearly cannot be learned
empirically at the time these decisions have to be made. While in the
former case, it may help to have a look at what others are doing, that
strategy is of no avail in the latter case. And even in the former
case the appeal to the possibility of learning from others only pushes
the problem one step further because "[i]mitation is useless unless
those imitated have themselves solved the problem of the adaptive
regulation of behavior" (Cosmides and Tooby 1987, 295).

As Ermer et al. (2007) have put the point, the problem for
domain-general cognitive architectures is that we are living in
"clueless environments":

Content-free architectures are limited to knowing what can be
validly derived by general processes from perceptual information
available during an individual's lifetime. This sharply limits the
range of problems they can solve: When the environment is clueless,
the mechanism will be, too. Domain-specific mechanisms are not limited
in this way. They can be constructed to embody clues that fill in the
blanks when perceptual evidence is lacking or difficult to obtain
(Ermer et al. 2007, 157).

At this point, a natural question to ask for the critic would be how
natural selection is supposed to operate if "relevant fitness
information" is indeed not available. As Buss puts it: would the
result of a really "clueless environment" not be extinction, rather
than adaptation?

Cosmides and Tooby's third argument for the claim that domain-general
systems could not live up to the tasks our mind regularly solves
concerns the general computational problems faced by such systems. As
they put it, a domain-general architecture "is defined by what it
lacks: It lacks any content, either in the form of domain-specific
knowledge or domain-specific procedures, that can guide it toward the
solution of an adaptive problem" (Cosmides and Tooby 1994, 94).
Therefore, they argue, a domain-general system must evaluate all
alternatives it can define, and this raises an obvious problem:
"Permutations being what they are, alternatives increase exponentially
as the problem complexity increases. By the time you analyze any
biological problem of routine complexity, a mechanism that contains no
domain-specific rules of relevance, procedural knowledge, or
privileged hypotheses could not solve the problem in the amount of
time the organism has to solve it" (Cosmides and Tooby 1994, 94).
Given that a specialization-free architecture contains no rules of
relevance, or domain-specialized procedural knowledge, to restrict its
search of a problem space, it could not solve any biological problem
of routine complexity in time.

These theoretical considerations (see Samuels 1998 and Buller 2005,
ch. 4 for criticism), together with the empirical support for the
modularity hypothesis that comes from cognitive science (see section
1b), have led Evolutionary Psychologists to the conclusion that "the
mind is organized into modules or mental organs, each with a
specialized design that makes it an expert in one area of interaction
with the world" (Pinker 1997, 21). The mind is a Swiss Army knife
containing evolved, functionally specialized computational devices
like, for example, "face recognition systems, a language acquisition
device, mindreading systems, navigation specializations, animate
motion recognition, cheater detection mechanisms, and mechanisms that
govern sexual attraction" (Cosmides and Tooby 2003, 63).

Although there can be little doubt that the mind is modular to some
extent, it is currently a hotly debated question exactly how modular
it is. Is it really massively modular in the sense that it is a
collection of hundreds or thousands of modules, or is it modular in a
weaker sense (see, for example, the debate between Carruthers 2006,
Prinz 2006, and Samuels 2006)? Interestingly, even the most ardent
advocates of Evolutionary Psychology have recently acknowledged that
"[t]he mind presumably does contain a number of functionally
specialized programs that are relatively content-free and
domain-general," but they have insisted that "these can regulate
behavior adaptively only if they work in tandem with a bevy of
content-rich, domain-specialized ones …" (Ermer et al. 2007, 156; see
also Tooby and Cosmides 1998, 200).

e. Human Nature

According to Evolutionary Psychologists, since the modules of which
the human mind is made up have been constantly selected for during a
vast stretch of time there is ample reason to think that "human
universals … exist at the level of the functionally described
psychological mechanism" (Tooby and Cosmides 1989, 36; italics added).
That is, the modules discovered by functional analysis constitute "an
array of psychological mechanisms that is universal among Homo
sapiens" (Symons 1992, 139), they are "the psychological universals
that constitute human nature" (Tooby and Cosmides 1990a, 19). As a
consequence, Evolutionary Psychology has the potential to discover a
"human nature [that] is everywhere the same" (Tooby and Cosmides 1992,
38).

Apart from the observation that enough time has passed with constant
selection pressures for our cognitive modules virtually being driven
to fixation, Cosmides and Tooby have offered two arguments for the
universality of our psychological adaptations (see also Buller 2005,
73–4). The first argument is more or less a plausibility argument,
according to which since our bodies and our minds are both the result
of evolution by natural selection, and our bodies are universal, so
should be our minds:

[T]he fact that any given page out of Gray's Anatomy describes in
precise anatomical detail individual humans from around the world
demonstrates the pronounced monomorphism present in complex human
physiological adaptations. Although we cannot directly 'see'
psychological adaptations …, no less could be true of them. (Tooby and
Cosmides 1992, 38)

The second argument first appeared in Tooby and Cosmides (1990a), has
been repeated in Tooby and Cosmides (1992) and is treated by
Evolutionary Psychologists as a definite proof of universal panhuman
design. In a nutshell, the argument is that since in sexual
reproduction a child's genome is a mixture of its father's and its
mother's genes, and since cognitive adaptations are complex and thus
not coded for by a single gene but require hundreds or thousands of
genes to work in concert for their development, "it is improbable that
all of the genes necessary for a complex adaptation would be together
in the same individual if the genes coding for the components of
complex adaptations varied substantially between individuals" (Tooby
and Cosmides 1992, 78–9).

If there is a complex series of interdependent adaptations
required to produce a sex, a behavioral strategy, or a personality
type, there is only one way to ensure the necessary coordination. All
of the parts of the genetic programs necessary to build the integrated
design must be present when needed in every individual of a given
type. The only way that the 50 genes, or 100 genes, or 1,000 genes
that may be required to assemble all of the features defining a given
type can rely on each other's mutual presence is that they are all
present in every individual. (Tooby and Cosmides 1990a, 45)

Evolutionary Psychologists are thus not claiming that human behavior
or culture is the same everywhere. Quite obviously, there is
significant behavioral and cultural diversity throughout the world.
What they claim is that the genes that are required for our cognitive
adaptations to develop, and thus the cognitive adaptations themselves,
must be the same all over the world, although, of course, the behavior
that results from them may differ (for more on this, see section 4a).

3. Examples of Empirical Research

Evolutionary Psychology has sparked an enormous amount of empirical
research covering nearly any imaginable topic, including issues as
diverse as language, morality, emotions, parental investment,
homicide, social coercion, rape, psychopathologies, landscape
preferences, spatial abilities, or pregnancy sickness (see, for
example, Buss 1999, 2005; Barkow et al. 1992 for an overview).

For instance, Margie Profet (1992) has argued that pregnancy
sickness—a set of symptoms like food aversion, nausea, and vomiting
that some women experience during the first three months of
pregnancy—is an adaptation for protecting the embryo against maternal
ingestion of toxins abundant in natural foods by lowering the typical
human threshold of tolerance to toxins during the period of the
embryo's maximum susceptibility to toxins. Irwin Silverman and Marion
Eals (1992) have argued that from an evolutionary point of view the
male advantage in spatial abilities usually found in psychological
experiments does not make sense. Although hunting, the primary task of
our male ancestors, clearly required spatial abilities, no less is
true of gathering plants, the primary task of our female ancestors. In
order to be efficient foragers, our female ancestors must have been
able to encode and remember the locations of thousands of different
plants. When Silverman and Eals designed spatial tests that measured
subjects' ability to recall the location of items in a complex array
or objects in a room, they found that women indeed consistently
recalled more objects than men did, and recalled their location more
accurately.

David Buss has argued that there are major differences between males
and females regarding mate choice and jealousy that are evolved
responses to different selection pressures (see, for example, Buss
1992, 1994, 2000; Buss and Schmitt 1993). For instance, he reasoned
that because men need to guard against cuckoldry, while women need to
guard against losing their mate's economic resources, men should be
concerned more by signs of sexual infidelity than about the loss of
their partner's emotional attachment, while women should be troubled
more by cues that signal emotional infidelity than by signs of sexual
infidelity. Buss et al. (1992) asked males and females from the USA,
Europe and Asia whether they would be more distressed by sexual or
emotional infidelity:

Please think of a serious committed romantic relationship that you
have had in the past, that you currently have, or that you would like
to have. Imagine that you discover that the person with whom you've
been seriously involved became interested in someone else. What would
distress or upset you more (please circle only one):

(A) Imagining your partner forming a deep emotional attachment to
that person.

(B) Imagining your partner enjoying passionate sexual intercourse
with that other person.

(Buss et al. 1992, 252)

Nowhere did women report sexual infidelity to be more upsetting than
men, and on average, 51% of the men, but only 22% of the women chose
option B above (for data and critical discussion, see Buller 2005,
316–45). These results have been taken to confirm Buss' evolutionary
hypothesis about sex differences with regard to jealousy (for a
dissenting view see, for example, DeSteno and Salovey 1996; Harris and
Christenfeld 1996).

The flagship example of Evolutionary Psychology is still Cosmides and
Tooby's work on cheater detection. In the 1960s, the Swedish
psychologist Peter Wason devised the so-called "Wason Selection Task"
in order to investigate how good subjects are at checking conditional
rules (Wason 1966). He gave subjects a rule of the form "If P, then Q"
(for example, "If a person goes to Boston, then that person takes the
subway"), and showed them four cards. Two of the cards exemplified the
P- and not-P-option, respectively (for example, "Boston" and "New
York"), and two of them exemplified the Q and not-Q-option,
respectively (for example, "subway" and "cab"). The subjects were told
that the unseen sides of the P and not-P-cards could contain an
instance of either Q or not-Q, and vice versa, and that they should
indicate all and only the cards that would definitely have to be
turned over in order to determine whether they violated the rule.
Since a material conditional is false if and only if its antecedent is
true and its consequent is false, the logically correct response would
be to pick the P- and the not-Q-card. However, Wason discovered that
most subjects choose either only the P-card or the P- and the Q-card,
while few choose the P- and the not-Q-card. More importantly,
subjects' performance was apparently influenced by the content of the
rules. While 48% correctly solved the Boston/transportation problem,
successful performance dropped to less then 25% for the rule "If a
person has a 'D' rating, then his documents must be marked code '3′"
(with the options 'D', 'F', '3′, '7′), and increased to nearly 75% for
the rule "If a person is drinking beer, then he must be over 21 years
old" (with the options "drinking beer," "drinking coke," "25 years
old," "16 years old") (Cosmides and Tooby 1992, 182–3). By the 1980s,
the psychological literature was full with reports of such "content
effects," but there was no satisfying theory to explain them.

Evolutionary biologists had long been puzzled by our ability to engage
in altruistic behavior—behavior an individual A performs for the
benefit of another individual B, associated with some significant cost
for A (like warning calls, help in raising offspring, saving a
drowning child, and so forth). How could a tendency to behave in a way
that increases another individual's fitness at some non-negligible
cost to oneself be produced and retained by natural selection? Robert
Trivers (1971) argued that altruistic behavior can evolve if it is
reciprocal, that is, if A's act a has benefit bB for B and cost cA for
A, B reciprocates with some act a* with benefit bA for A and cost cB
for B, where bA outweighs cA and bB outweighs cB. Interactions that
satisfy this cost-benefit structure constitute what is called a
"social exchange." Since in social exchanges both A and B incur a
net-benefit, Trivers reasoned, altruistic behavior can evolve. Yet,
the problem is that once a propensity for altruistic behavior has
evolved, it is obviously better for an individual to cheat by
accepting the benefit of an altruistic act without paying the cost of
reciprocation. In the long run, this would lead to an increase in the
number of cheaters until altruism was driven to extinction. In order
for altruism to evolve, Trivers (1971, 48) concluded, natural
selection must "favor more acute abilities to detect cheating."

Cosmides and Tooby saw a connection between the need to detect
cheaters in acts of social exchange and the content effect discovered
by Wason (Cosmides 1989; Cosmides and Tooby 1989, 1992). Since the
ability to test abstract logical rules would not have had any adaptive
value in the EEA, we should not expect natural selection to have
endowed the human mind with some general conditional reasoning
capacity. Rather, natural selection should have designed a module that
allows us to detect those who accept the benefit without reciprocating
accordingly in situations of social exchange. Consequently, we should
be better at testing social contract rules that say "If person A
provides the requested benefit to or meets the requirement of person
or group B, then B will provide the rationed benefit to A" (Cosmides
and Tooby 2000, 1260) than at testing conditional rules that do not
describe such conditions.

When Cosmides and Tooby categorized "content effects according to
whether they conformed to social contracts, a striking pattern
emerged. Robust and replicable content effects were found only for
rules that related terms that are recognizable as benefits and
cost/requirements in the format of a standard social contract"
(Cosmides and Tooby 1992, 183). They argued that the content effect
found in Wason Selection Tasks is due to the fact that some tasks
involve a social contract rule.

In order to substantiate this hypothesis, they conducted a series of
experiments designed to rule out alternative explanations of the
content effects. One plausible explanation, for instance, would be
that our cognitive system is able to deal better and more effectively
with familiar problems (like the drinking/age problem) than with
unfamiliar problems (like the letter/number problem). They therefore
compared performance on unfamiliar social rules with performance on
unfamiliar non-social rules. If familiarity is the issue, then
subjects should perform equally bad on both unfamiliar rules. If,
however, the increased performance in the drinking/age problem is due
to the fact that here the subjects are dealing with a social contract
rule, then performance should be better on the unfamiliar social than
on the unfamiliar non-social rule.

Cosmides designed two unfamiliar Wason Selection Tasks. One rule read
"If a man eats cassava root, then he must have a tattoo on his face"
(with the options "eats cassava root," "eats molo nuts," "tattoo," "no
tattoo"). The other read "If you eat duiker meat, then you have found
an ostrich eggshell" (with the options "duiker," "weasel," "ostrich
eggshell," "quail eggshell"). The first was accompanied by a story
according to which the inhabitants of a Polynesian island have strict
sexual mores that prohibit sex between unmarried people and thus mark
married men with a facial tattoo and do not permit unmarried men to
eat cassava root, which is a very powerful aphrodisiac. The second
story said that anthropologists who notice that the natives frequently
say that if someone eats duiker meat, then he has found an ostrich
shell hypothesize that this is because duikers often feed on ostrich
shells. Thus, the first rule clearly represents a social
contract—having a tattoo is the requirement one has to meet if one is
being permitted the benefit of eating cassava root—while the second is
a non-social rule which simply expresses the hypothesis that duikers
and ostrich eggs are frequently found in close proximity.

The results confirmed the cheater detection prediction (Cosmides and
Tooby 1992, 186–7): 75% correctly answered the unfamiliar social
problem, but only 21% the unfamiliar non-social problem.

Cosmides also hypothesized that if there is a cheater detection
module, then subjects should pick the cards that represent cheating
even if they correspond to the logically incorrect answer. She thus
switched the logical role of the P/not-P- and the Q/not-Q-cards in
both the cassava root/tattoo and the duiker meat/ostrich shell
problem. The switched rules read "If a man has a tattoo on his face,
then he eats cassava root" and "If you have found an ostrich eggshell,
then you eat duiker meat." Since the not-P- and the Q-card ("no
tattoo" and "eats cassava root") still represent accepting a benefit
without meeting the requirement, the cheater detection hypothesis
predicts that subjects should pick the logically incorrect cards in
the first case, whereas performance in the ostrich shell/duiker meat
case should be unaffected. Again, the prediction was confirmed
(Cosmides and Tooby 1992, 188–9): 67% of the subjects chose the
logically incorrect not-P- and Q-cards in response to the switched
social problem, but only 4% did so for the switched non-social
problem. (For a criticism of Cosmides and Tooby's work on cheater
detection and for further references see Buller 2005, 163–90.)

4. Problems and Objections

Evolutionary Psychology is a successful research program, but it has
its problems. Some difficulties have already been mentioned in section
2 in connection with the theoretical underpinnings of Evolutionary
Psychology (for a recent critique of Evolutionary Psychology at a
methodological and conceptual level see Panksepp and Panksepp 2000).
These and a couple of others will be briefly reviewed in this section.

a. Genetic Determinism

One of the most often heard criticisms is also one of the least
convincing. The charge is that Evolutionary Psychology is committed
to, or at least willfully embraces, a genetic determinism according to
which our behavior is determined by our genetic make-up, which, since
it is a human universal, cannot be influenced by means of social
learning, education, and so forth, Dorothy Nelkin (2000, 27), for
instance, claims that Evolutionary Psychology implies "genetic
destiny," and Robin Dunbar maintains that it seems "to be looking for
genetically determined characters that are universally valid for all
humans," observing that this makes little sense because the "number of
genuinely universal traits are … likely to run to single figures at
most" (Dunbar 1988, 168).

It is true that Evolutionary Psychologists are looking for human
universals, and it is also true that they think that if humans were
not genetically very similar, there could be no cognitive adaptations
(see section 2e). Yet, they are not committed to "a form of 'genetic
determinism,' if by that one means the idea that genes determine
everything, immune from an environmental influence" (Tooby and
Cosmides 1990a, 19). Their claim is that the cognitive mechanisms
underlying behavior are human universals, and that does not entail
that our behavior is genetically determined, or the same all over the
world. Quite the contrary: It is universally agreed among Evolutionary
Psychologists that behavior, like any other human trait, is the result
of the complex interplay between genetic and environmental factors.
Genetic determinism is false because "every feature of every phenotype
is fully and equally codetermined by the interaction of the organism's
genes … and its ontogenetic environments" (Tooby and Cosmides 1992,
83; italics added), as is nicely illustrated by the fact that not even
genetic clones, monozygotic twins, are phenotypically identical. In
fact, work in Evolutionary Psychology has emphasized the highly
flexible and contingent nature of cognitive adaptations. For instance,
Martin Daly and Margo Wilson's often cited work on violence toward
children by stepparents (for example, Daly and Wilson 1988a, 1988b) is
in fact entirely concerned with contextual factors—the presence of a
stepparent in a household, they argue, is one of the primary
predictors of fatal violence toward children.

b. Moral and Societal Issues

A related charge is that Evolutionary Psychology is defending the
status quo regarding sex, race, intelligence differences, and so
forth, by arguing that, first, there is nothing we can do, given that
these differences are the result of our hard-wired cognitive
mechanisms, and, second, there is no need to do something, because
these differences, being the result of natural selection, are optimal
solutions to longstanding adaptive problems.

The first claim is just wrong. As seen in section 4a, it is not "all
in our genes" because the environment heavily influences what behavior
issues forth from cognitive mechanisms, even if the latter are
evolutionarily hard-wired.

The second claim is an instance of what many scholars would regard as
the fallacious inference from "is" to "ought" (see Naturalistic
Fallacy). As Robert Kurzban (2002) has pointed out, Evolutionary
Psychologists are well aware that it is illegitimate to move from the
first to the second, that there is a difference "between science,
which can help us to understand what is, and morality, which concerns
questions about what ought to be." Regarding cognitive adaptations,
one cannot infer "ought" from "is" because (1) there is no guarantee
that natural selection always finds an optimal solution, (2) since the
environment has changed, something that was good for our ancestors may
no longer be good for us, and (3) the sense in which it was "good" for
our ancestors that, say, they possessed a cognitive mechanism that
pre-disposed them to kill children of their mating partners that were
not their own ("good" in the sense of "fitness increasing") is
definitely not the sense of "good" that is relevant to ethical
discourse ("good" in the sense of "morally praiseworthy/obligatory").

c. Untestability and Story Telling

One of the key problems for Evolutionary Psychologists is to show that
the adaptationist explanations they offer are indeed explanations
properly so called and not mere "just-so-stories" that feature
plausible scenarios without its being certain that they are historical
fact. Stephen Jay Gould, for instance, who famously criticized
evolutionary biology for its unreflected and widespread adaptationism
that tends to ignore other plausible evolutionary explanations (Gould
and Lewontin 1979), has argued that the sole task of Evolutionary
Psychology has become "a speculative search for reasons why a behavior
that harms us now must once have originated for adaptive purposes"
(Gould 2000, 119).

There is something to this charge, but things are more difficult.
Evolutionary Psychologists stress that "[i]t is difficult to reconcile
such claims with the actual practice of EP, since in evolutionary
psychology the evolutionary model or prediction typically precedes and
causes the discovery of new facts, rather than being constructed post
hoc to fit some known fact" (Sell et al. 2003, 52). The discussion of
functional analysis in section 2b has shown that there is a clear
sense in which adaptationist hypotheses can be tested: functional
analysis predicts the existence of yet unknown cognitive mechanisms on
the grounds of evolutionary reasoning about potential adaptive
problems in the EEA, and these predictions are then empirically
tested. The hypotheses Evolutionary Psychologists derive from their
computational theory thus allow them "to devise experiments that make
possible the detection and mapping of mechanisms that no one would
otherwise have thought to test for in the absence of such theories"
(Sell et al. 2003, 48). It is therefore not true that "claims about an
EEA usually cannot be tested in principle but only subjected to
speculation" (Gould 1997, 51) because if the purported cognitive
mechanisms fail to show up in psychological experiments, the
adapationist explanation is falsified.

First, however, this holds only for research that conforms to Cosmides
and Tooby's theoretical model (arguably, Cosmides and Tooby's work on
cheater detection, Buss' work on sex differences with regard to
jealousy, and Silverman and Eals' work on differences in spatial
abilities belong to this category). It does not apply to research that
does not generate a prediction based on a putative problem, but tries
to infer the historical function of an organism's traits from its
current structure. Profet's work on pregnancy sickness would be a case
in point: here, one already knows the trait (pregnancy sickness) and
merely speculates about its historic function, in contrast to the
other cases, where the existence of the trait (an ability to detect
cheaters, sex specific responses to jealousy, or sex specific spatial
abilities) is inferred from evolutionary considerations about the
problems prevalent in the EEA.

Second, the controversial claim is not that our psychological
faculties have evolved. It is that they are adaptations, and, more
specifically, adaptations for solving particular adaptive problems.
Successful psychological tests that show that current Homo sapiens
indeed possesses the hypothesized cognitive mechanisms establish that
these traits have evolved, but they fail to establish that they are
adaptations, let alone adaptations for, say, detecting cheaters or
remembering the location of edible plants. For all these tests tell
us, the traits in question could still be exaptations, or even
spandrels. In order to show that they are indeed adaptations, a point
that is forcefully made by Richardson (2008), additional information
would be needed, and it is not clear that this additional information
can be had (for a sketch of Richardson's argument see Walter 2009).

Third, there seems to be a sense in which adaptationist explanations
are still "just-so-stories." Functional analysis relies on claims
about the nature of the EEA which cannot be directly verified because
there is very little we can know with any confidence about the
conditions that obtained in the EEA. As Evolutionary Psychologists
like to point out, there are some things which have arguably stayed
constant since the EEA:

[R]esearchers know with certainty of high confidence thousands of
important things about our ancestors, many of which can be used to
derive falsifiable predictions about our psychological architecture:
our ancestors had two sexes; contracted infections by contact,
collected plant foods; inhabited a world where the motions of objects
conformed to the principles of kinematic geometry; had color vision;
were predated upon; had faces; lived in a biotic environment with a
hierarchical taxonomic structure, and so forth (Sell et al. 2003,
52–3).

The problem is that knowing that our ancestors inhabited a world with
two sexes where the motions of objects conformed to the principles of
kinematic geometry does not enable us to formulate the adaptive
problems our ancestors putatively faced in enough detail. Both our
male and female ancestors lived in such a world (as, by the way, did
the ancestors of apes, spiders and flies), and yet they evolved
different mating strategies, different responses to emotional versus
sexual infidelity, different spatial abilities, and so forth. The
descriptions of the past adaptive problems that Evolutionary
Psychologists rely on in order to explain these differences are much
more specific than the platitudes of which we can be relatively
certain, and it is unclear how we could ever be confident that we got
the specific details right. As Stephen Jay Gould puts it vividly:

But how can we possibly know in detail what small bands of
hunter-gatherers did in Africa two million years ago? These ancestors
left some tools and bones, and paleoanthropologists can make some
ingenious inferences from such evidence. But how can we possibly
obtain the key information that would be required to show the validity
of adaptive tales about an EEA: relations of kinship, social
structures and sizes of groups, different activities of males and
females, the roles of religion, symbolizing, storytelling, and a
hundred other central aspects of human life that cannot be traced in
fossils? (Gould 1997, §31; see also Gould 2000, 120)

In the case of Buss' research on the evolution of sex differences with
regard to jealousy, for instance, we can only hypothesize about such
things as group structure and size, mating structures, similarities
between ancestral and current group structures, or the alleged
differences in mating behavior in ancestral groups that are appealed
to or presupposed in the formulation of the adaptive problem (again, a
point made convincingly by Richardson 2008).

Of course, as Sell et al. (2003) point out, if our assumptions about
our ancestors' problems are wrong, our computational theory is wrong,
too, and should thus predict the existence of cognitive mechanisms
that will not be found when checked for empirically. Yet, even if this
is so, the two qualifications above apply to this move mutatis
mutandis. (For more on the role of historical evidence in the search
for adaptations and the kinds of problems that may arise, see Kaplan
2002.)

d. Psychological Inadequacy

In Adapting Minds: Evolutionary Psychology and the Persistent Quest
for Human Nature, David Buller argues "not only that the theoretical
and methodological doctrines of Evolutionary Psychology are
problematic, but that Evolutionary Psychology has not, in fact,
produced any solid empirical results" (Buller 2005, 15). What is wrong
with Evolutionary Psychology is that the psychological experiments
used to establish the existence of the hypothesized cognitive
mechanisms in current Homo sapiens are flawed because the data are
exiguous, inconclusive and do not support the claims made by
Evolutionary Psychologists, as Buller tries to show in detail for the
classical studies of Cosmides and Tooby, Buss, and Daly and Wilson on
cheater detection, mating strategies, jealousy, and discriminative
parenthood. Whereas Richardson (2008) claims that Evolutionary
Psychology is problematic as Evolutionary Psychology, Buller
challenges the psychological credentials of evolutionary psychology,
arguing that Evolutionary Psychology fails as Evolutionary Psychology.

5. Evolutionary Approaches to Mind, Culture, and Behavior:
Alternatives to Evolutionary Psychology

In its broad sense, evolutionary psychology attempts to adopt "an
evolutionary perspective on human behavior and psychology" (Barrett et
al. 2002, 1) by applying Darwinian reasoning to behavioral, cognitive,
social, or cultural characteristics of humans. Evolutionary Psychology
is one strand of evolutionary psychology, but there are others, and
the literature is full of different labels: "sociobiology,"
"evolutionary anthropology," "human behavioral ecology," "Darwinian
psychology," "gene-culture coevolution," to name just a few. These
approaches share the idea that evolutionary reasoning can enhance our
understanding of mind, culture, and society, but they disagree about
exactly how Darwinian thinking ought to enter the picture. This is not
the place to go into the details, but a brief survey of the
theoretical landscape (see Laland and Brown 2002 for a book-length
overview) may help to understand the difference between evolutionary
psychology as a general field of inquiry and Evolutionary Psychology
as a narrowly circumscribed research paradigm.

a. Human Behavioral Ecology

Evolutionary Psychologists insist that an evolutionary approach to
human psychology must ask whether a trait is an adaptation, not
whether it is currently adaptive. They thereby separate themselves
sharply from an approach Symons (1989) dubbed "Darwinian anthropology"
that instead focuses on the current adaptiveness of our behavior (for
a more reconciliatory approach see, for example, Downes 2001). Human
behavioral ecology, as it is nowadays called (Borgerhoff Mulder 1991),
originated in the late 1970s when, after the upheaval caused by
Wilson's Sociobiology, some anthropologists decided to go out and test
the controversial hypotheses of Wilson and others by means of real
data from hunter-gatherer populations (Chagnon and Irons 1979; Hinde
1974). Using quantitative ethnographic information and optimality
models, human behavioral ecologists investigate whether and how the
current adaptiveness of an individual's behavior is influenced by its
ecological and cultural environment and in which way the different
behaviors individuals develop to cope with environmental challenges
lead to and account for cultural differences between them.

Natural selection, human behavioral ecologists argue, has created an
extraordinary flexibility—known as phenotypic plasticity—that allows
our "behavior to assume the form that maximizes inclusive fitness"
(Irons 1979, 33) across a wide variety of widely diverse habitats.
Since there has been selection for a general phenotypic plasticity, we
are not so much "adaptation executers" as rather "fitness maximizers":
"Modern Darwinian theory predicts that human behavior will be …
designed to promote maximum reproductive success" (Turke and Betzig
1985, 79; italics added). As a consequence, human behavioral
ecologists are less interested in discovering proximal cognitive
mechanisms than in checking whether the behavior they trigger is
actually adaptive (a strategy known as phenotypic gambit).

b. Memetics

A rather different approach is adopted by memetics (Blackmore 1999;
Distin 2005). Memetics tries to explain cultural characteristics and
processes and the way they influence our behavior by postulating a
process of cultural evolution that is analogous to the process of
biological evolution, but largely independent of it. Dawkins (1976)
introduced the idea that evolution by natural selection is a substrate
neutral process that can act on what he called a "replicator," that
is, any heritable entity for which there is variation in a population
and that is associated with different degrees of fitness. The gene,
Dawkins said, is the replicator in biological evolution, but the
cultural realm also has a replicator, which he famously dubbed a meme:
a meme is "a unit of cultural inheritance, hypothesized as analogous
to the particulate gene, and as naturally selected in virtue of its
phenotypic consequences on its own survival and replication in the
cultural environment" (Dawkins 1982, 290). Memes form the substrate of
cultural evolution, a process in which different memes are
differentially transmitted from individual to individual. One of the
key challenges for memetics is to spell out exactly what memes are,
and although suggestions abound, there is no agreed consensus [for
instance, according to Dawkins "examples of memes are tunes, ideas,
catch-phrases, clothes fashions, ways of making pots or of building
arches" (Dawkins 1976, 206), while Dennett (1995, 347–8) cites the
ideas of the wheel, of wearing clothes, the vendetta, the right
triangle, the alphabet, chess, perspective drawing, Impressionism,
Greensleeves, and deconstructionism as examples]. Importantly,
whatever memes are, they must be sufficiently similar to genes to
warrant the claim that cultural evolution is more or less analogous to
biological evolution, and critics of memetics argue that this
constraint is unlikely to be met (for example, Boyd and Richerson
2000; for a more optimistic view, see Blackmore 1999, ch. 5).

c. Gene-Culture Coevolution

Defenders of what is known as "gene-culture coevolution" or "dual
inheritance theory" (Boyd and Richerson 1985, 2005a, 2005b;
Cavalli-Sforza and Feldmann 1981; Durham 1991) agree with memetics
that transmitted cultural information is too important a factor to be
ignored by an evolutionary approach to human culture and behavior.
After all, one of the most striking facts about humans is that there
are important and persistent differences between human groups that are
due to culturally transmitted ideas, and not to genetic, biological,
or ecological factors. Yet, although culture is a Darwinian force in
its own right, they argue, there is no substantial analogy between
cultural and biological evolution. In both processes information is
transmitted between individuals and both create patterns of heritable
variation, but the differences are much more salient: culture is not
based on direct replication but upon teaching, imitation, and other
forms of social learning, the transmission of culture is temporally
extended and not restricted to parents and their offspring, cultural
evolution is not necessarily particulate, and not necessarily random
(Boyd and Richerson 2000).

Culture is part of human biology, gene-culture coevolutionists argue,
but accounts concerned solely with genetic factors are inadequate
because they ignore the fact that culture itself shapes the adaptive
environment in which biological evolution takes place by creating a
culturally constructed environment in which human genes must evolve.
Conversely, accounts aimed solely at explaining cultural replication
are also inadequate because they ignore the fact that genes affect
cultural evolution, for instance by forming psychological
predispositions that bias what people imitate, teach, or are able to
learn. Hence, a truly evolutionary approach to culture must
acknowledge that genesand culture coevolve, and try to investigate the
circumstances under which the cultural habits adopted by individuals
are influenced by their genes, and how the natural selection pressures
that guide biological evolution may be generated by culture.

6. References and Further Reading

a. Suggested Further Reading

* Barkow, Jerome, Leda Cosmides, and John Tooby, eds. (1992). The
Adapted Mind: Evolutionary Psychology and the Generation of Culture.
Oxford: Oxford University Press.

The manifesto of Evolutionary Psychology.
* Barrett, Louise, Robin Dunbar, and John Lycett, eds. (2002).
Human Evolutionary Psychology. Princeton, NJ: Princeton University
Press.

A very useful textbook of evolutionary psychology in the broad
sense, covering both Evolutionary Psychology and Human Behavioral
Ecology.
* Buller, David (2005). Adapting Minds: Evolutionary Psychology
and the Persistent Quest for Human Nature. Cambridge, MA: MIT Press.

A philosophical critique of Evolutionary Psychology, arguing
that the empirical tests Evolutionary Psychologists rely on to
establish that current Homo sapiens possesses the postulated cognitive
adaptations in the areas of cheater detection, mating, marriage, and
parenthood are flawed.
* Buss, David (1999). Evolutionary Psychology: The New Science of
the Mind. Boston: Allyn and Bacon.

The textbook of Evolutionary Psychology, written by one of its
most ardent advocates.
* Cosmides, Leda, and John Tooby (1992). "Cognitive Adaptations
for Social Exchange." In: The Adapted Mind: Evolutionary Psychology
and the Generation of Culture. Eds. Jerome Barkow, Leda Cosmides, and
John Tooby. Oxford: Oxford University Press, 163–228.

The classic paper on cheater detection.
* Dawkins, Richard (1976). The Selfish Gene. Oxford: Oxford
University Press.

A must-read for anyone interested in evolutionary biology in
general, in which Dawkins introduces the concept of the meme and
defends his theory of evolution from the gene's eye point of view
(also known as the "selfish gene theory") according to which the
ultimate beneficiary of the evolutionary process is neither the
species, nor the individual, nor a particular trait, but the gene.
* Laland, Kevin, and Gillian Brown (2002). Sense or Nonsense:
Evolutionary Perspectives on Human Behavior. Oxford: Oxford University
Press.

A highly laudable introduction to sociobiology, Evolutionary
Psychology, human behavioral ecology, memetics, and gene-culture
coevolution.
* Pinker, Steven (1997). How the Mind Works. New York: Norton.

A very accessible introduction to Evolutionary Psychology and to
the kinds of issues discussed in cognitive science in general.
* Pinker, Steven (2002). The Blank Slate: The Modern Denial of
Human Nature. New York: Penguin.

Another very accessible introduction to the ideas of
Evolutionary Psychology, written by one of the most gifted writers in
academia.
* Richardson, Robert (2008). Evolutionary Psychology as Maladapted
Psychology. Cambridge, MA: MIT Press.

A philosophical critique of Evolutionary Psychology from the
perspective of evolutionary biology.
* Samuels, Richard (1998). "Evolutionary Psychology and the
Massive Modularity Hypothesis." British Journal for the Philosophy of
Science, 49, 575–602.

Criticizes Evolutionary Psychology's insistence on the
domain-specificity of cognitive mechanisms, arguing that a
domain-general architecture that uses domain-specific information
would be equally good.
* Tooby, John, and Leda Cosmides (1990a). "On the Universality of
Human Nature and the Uniqueness of the Individual: The Role of
Genetics and Adaptation." Journal of Personality, 58, 17–67.

Contains Cosmides and Tooby's genetic argument (discussed in
section 2e) for the claim that our cognitive adaptations are human
universals.
* Tooby, John, and Leda Cosmides (2005). "Conceptual Foundations
of Evolutionary Psychology." In: The Handbook of Evolutionary
Psychology. Ed. David Buss. Hoboken, NJ: Wiley, 5–67.

A brief, but very valuable overview over the theoretical
background of Evolutionary Psychology.
* Wright, Robert (1994). The Moral Animal. The New Science of
Evolutionary Psychology. New York: Pantheon Books.

A simplifying introduction to Evolutionary Psychology, written
for a general audience, included here under "Suggested Readings" only
to stress that it is not to be recommended at all for anyone with a
serious interest in Evolutionary Psychology.

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