Evolutionary Psychology

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Evolutionary Psychology
Evolutionary psychology is a recent approach to understanding human psychology that takes as
its starting place the fact that minds, just like hearts, kidneys, eyes, and thumbs, are the products
of evolution. As banal as this point may seem, evolutionary psychologists believe that an
evolutionary perspective on psychology implies an array of ontological and methodological
commitments that sharply distinguishes evolutionary psychology from other scientific theories of
mind. Among the more important of these commitments are that minds consist of many
(thousands, according to some) domain-specific modules that arose as adaptations during the
Pleistocene epoch (roughly 1.8 million years b.p. until 11.5 thousand years b.p.). These
adaptations are common to all human beings, and thus constitute a human nature. Study of these
adaptations requires hypotheses about features of the environment of evolutionary adaptedness
(EEA), as well as about which psychological properties exhibit design. Most celebrated by
evolutionary psychologists are the discoveries evolutionary psychologists have made in the areas
of mate preferences, social exchange, and parent-offspring conflict. Critics have charged that
evolutionary psychology is untestable because hypotheses about the EEA cannot be tested, that
evolutionary psychology is adaptationist to a fault, and that commitment to the existence of a
human nature is inconsistent with evolutionary theory.
1 Ontological commitments of evolutionary psychology
Brain size in the genus homo began to increase roughly 2 million years ago, which
corresponds, also roughly, to the beginning of the Pleistocene epoch. Because the time between
the end of the Pleistocene and the present day is too brief (a period of only about 550 human
generations) to have allowed much human evolution, it will have been during the Pleistocene
that modern human psychological traits evolved. Thus, the characteristics of human minds bear

an imprint of the Pleistocene environment. This fact, evolutionary psychologists believe, entails
certain consequences for human psychology.
Among these commitments is that human minds consist of many, perhaps thousands, of
domain-specific modules, each designed by natural selection in a way that will maximize the
reproductive success of the genes that produce them. Moreover, because these modules are
adaptations that have moved to fixation in the human population, they are features of a universal
human psychology. Let us examine these claims in turn.
Our Pleistocene ancestors faced numerous selection pressures. Evolutionary
psychologists refer to the selection pressures and problems that confronted our ancestors as the
environment of evolutionary adaptedeness (EEA). The EEA was not a fixed time or place.
Rather, it was the amalgam of changing geological, climatic, biotic, and, most importantly, social
conditions that had an impact on human survival. Some features of the human EEA might be
identical to features of other organisms’ EEAs. For example, our ancestors, as well as many
other organisms, had to find food, distinguish safe from toxic food, and raise offspring.
However, there were elements of the human EEA that generated specifically human
psychological adaptations. Human female ovulation is undetectable. Thus, reproductively
successful males were those who developed adaptative strategies to respond to hidden ovulation.
Human beings lived in social groups and sometimes benefited from the exchange of goods with
members of their groups. Thus, those human beings who developed the means by which to
detect whether they were being cheated would be fitter than those who did not. Similarly, those
who adopted an attitude of xenophobia toward members of other groups may have been spared
aggressive encounters.

The list of problems our ancestors faced in the EEA must be incredibly long: avoiding
incest, avoiding toxic foods, finding nutritious food, defeating aggressors, choosing a mate,
caring for children, inferring what others are thinking, preventing (or producing) deception,
gaining and keeping status, planning for the future, identifying predators, preventing cuckoldry,
and on and on. Each of these problems demands a solution that cannot serve as a solution to
other problems. In this way, psychological adaptations show their similarity to more familiar
anatomical and physiological adaptations. Lungs have the function of introducing oxygen into
the bloodstream, but they do not pump blood. Hands grasp, but feet do not. Some teeth are
specialized for tearing and others for grinding. Just as natural selection has crafted anatomical
and physiological traits for precise ends, so too the evolutionary psychologist expects that
psychological adaptations will be singularly dedicated to solving very particular kinds of
problems. Thus, there will be special collections of circuits in the brain – modules – that are
each devoted to processing particular kinds of information. For instance, evolutionary
psychologists have claimed that there is a module for the detection of sexual rivals (e.g. Buss,
Shackelford, Choe, Buunk, and Dijkstra 2000). This module presumably contains within it rules
about how to identify someone as a sexual rival and what actions to take to prevent this rival
from winning over one’s mate. In this sense, human beings come equipped with a jealousy
module. The system is modular because it is a devoted piece of computational machinery that
interacts with other modules only through clearly defined interfaces, and it is domain-specific
because it processes and responds only to information about sexual rivals and not about, e.g.
toxic food or predators.
In short, evolutionary psychology conceives the mind as comprising many such modules,
each one tailored to the solution of a particular adaptive problem that confronted our ancestors in

the EEA. These modules constitute a collection of psychological instincts that in many cases act
as automatically as the reflexes that keep flying particles from injuring our eyes, or food from
being aspirated.
The obvious contrast to a modular, domain-specific mind is the conception of mind that
comes to us from the empiricist tradition. On the empiricist view, the mind is a blank slate,
which is to say that it comes empty of any capacities to recognize particular objects or
circumstances. It contains no knowledge of how to choose between good and poor mates,
cheater and friend, predator and prey. Moreover, unlike the evolved mind, in which
computational circuits customize their processing to the specific kinds of information to which
they have been designed to respond, the empiricist mind relies on the same broad cognitive skills
– memory, attention, problem solving, reasoning – when considering content within any domain.
In contrast, evolutionary psychologists predict, and their data support the thesis, that human
capacities to recognize, remember, and attend will differ depending on subject matter. For
instance, human beings are very good at recognizing and remembering faces, but not nearly so
good at recognizing and remembering abstract geometrical designs. Presumably, this difference
is owing, on the one hand, to the clear adaptive benefit accruing to one who can recognize
members of his or her social group and, on the other hand, to the relative unimportance of being
able to recognize abstract geometrical designs.
When evolutionary psychologists claim that the domain-specific modules that constitute
the mind are adaptations, they mean that natural selection has been the main or exclusive cause
for their existence. This is a strong thesis, for natural selection need not always play the most
significant role in a trait’s evolution. Some traits evolve simply because they are byproducts of
traits for which there is selection (Gould and Lewontin 1979). These “spandrels” are typically a

necessary consequence of introducing new traits into an exquisitely integrated collection of
previously existing traits, but there are simple examples as well. Thus, the greenness of leaves is
a byproduct of the presence of chlorophyll, for which there was selection. Similarly, belly
buttons are anatomical features that serve no function but are the necessary consequence of an
umbilical attachment. We will see below that evolutionary psychologists have been criticized for
thinking that all psychological traits, or all interesting psychological traits, are adaptations.
But there is more to be said about adaptations. Adaptations are so-called because they
modify their possessors in a beneficial way. Because adaptations are beneficial, their possessors
will be fitter than those lacking the adaptation, and over time (but not always), all members of
the population will possess the adaptation. But this account of evolution leaves unidentified the
unit of selection, i.e. the beneficiary of the adaptation whose benefiting causes the evolution of
the adaptive trait. For the most part, Darwin thought that adaptations evolve as a result of their
benefit to individuals. The lion’s sharp claws benefit the lion. Many evolutionary psychologists,
however, believe that the gene is the only unit of selection (there are exceptions, notably Boyd
and Richerson 1985). Any benefit that sharp claws confer on a lion are also conferred on the
genes that code for the proteins from which the claws are constructed. This endorsement of the
selfish gene thesis (see Dawkins 1976), although widespread among evolutionary psychologists,
seems tangential to the main goals and interests of evolutionary psychology, and at any rate is
certainly not implied by the assumption that psychological traits are adaptations. A
psychological trait can benefit a cluster of genes while at the same time benefiting an individual,
and there appears to be no reason to limit an adaptation’s bounty to a single kind of entity.
Moreover, there is nothing to prevent an adaptive psychological trait from benefiting a group of
non-related conspecifics. As various models of group selection have revealed, altruistic

psychological traits can evolve (see especially Sober and Wilson 1998), and their existence
needn’t pose any threat to the evolutionary psychologist’s belief that the mind consists of
domain-specific, modular adaptations.
One final point about adaptations will conclude this section on the ontological
commitments of evolutionary psychology. Most or all psychological traits, evolutionary
psychologists believe, have zero heritability. This is because heritability, within evolutionary
biology, is defined as the proportion of phenotypic variation in a population that is a product of
genetic variation. When there is no phenotypic variation in a trait, there will consequently be no
heritability of the trait (although the trait was heritable during its period of evolution).
Adaptations are more likely to have low heritability because traits that increase fitness will often
move to fixation in a population. For example, opposable thumbs have nearly zero heritability
within human beings. On the other hand, traits like body hair, height, nose size, and eye color
have considerable heritability. This can be explained on the assumption that these latter traits do
not confer any, or any significant, selective advantage. They are free to vary without making
much difference to the fitness of their possessors.
The idea that psychological adaptations have zero heritability leads evolutionary
psychologists to defend the existence of a human nature. Because all or almost all psychological
traits are adaptations, and because all or most adaptations will be shared by all members of a
population, all or almost all human beings will have the same collection of domain-specific
psychological modules. The most obvious exceptions to this shared human nature that
evolutionary psychologists acknowledge are the differences one finds between male and female
psychologies. However, we should still expect, evolutionary psychologists believe, that there is

a common human nature that men and women share, and on top of this base there will exist a
male human nature and a female human nature.
2 Methodological commitments of evolutionary psychology
The explanatory goal of evolutionary psychology is a description of the domain-specific
modules that evolved as adaptations to the selection pressures in the EEA. This description will
entail first the discovery of the modules themselves, which involves a functional description of
the module, and second an information-processing account of how the modules perform their
functions. Evolutionary psychologists are careful to point out that their subject matter is not
human behavior, e.g. running from predators, eating nutritious food, choosing fertile mates,
because behavior is not an adaptation. Behavior cannot be an adaptation because behavior is not
heritable. Indeed, there are many behaviors that an organism will never exhibit despite having a
domain-specific mechanism that would trigger the behavior in appropriate circumstances. Thus,
the evolutionary psychologist’s focus is on the proximate causes of behavior, i.e. the domain-
specific modules that persist and evolve through generations.
The primary explanatory strategy in evolutionary psychology is the task (or functional)
analysis. The strategy begins with an attribution of a function to the target of one’s analysis. The
function assignment then guides an analysis of the target capacity into simpler capacities. The
resulting analysis counts as an explanation of the target because it describes how the behavior of
the target is produced by the interaction of its simpler components. The assumption that
psychological traits are adaptations that evolved in the EEA provides a means by which to
constrain task analyses, thereby enhancing their effectiveness.
For example, in providing a task analysis of a grandfather clock, one starts with the
assumption that the clock’s mechanism has the purpose of keeping time. This function

assignment guides subsequent analysis, revealing why the pendulum is the length that it is, why
the escapement gear has the number of teeth it does, why the gear train has the ratio it does, and
so on. Indeed, knowledge that the clock is designed to tell time allows one to predict the number
of teeth on the escapement gear given the period of the pendulum. Without knowing that the
mechanism in the clock is designed to tell time, the facts listed in the task analysis of the
grandfather clock lack unity – their relationship to each other is simply brute.
Grounding the function assignments on which evolutionary psychologists depend for
their analyses of psychological modules are assumptions about the selection pressures that our
Pleistocene ancestors faced. Some of these assumptions emerge purely from speculation about
what the EEA must have been like and how our ancestors must have evolved given that they
successfully reproduced. For instance, it is a very safe bet that our ancestors must have
developed adaptations for hunting, gathering, mate selection, incest avoidance, parental care, and
cooperation. Of course, simply knowing that our ancestors faced competition for mates does not
reveal much about the psychological adaptations that evolved in response to this problem.
However, evolutionary psychologists can test hypotheses about the adaptive functions of
psychological modules by collecting observations about current human behavior. Because
psychological modules cause behavior that would have been adaptive in the EEA, experiments
designed to reveal this behavior will provide evidence about the function of the module. Thus,
evolutionary psychologists have performed studies that purport to show that men fantasize about
sex more than women and prefer nubile, promiscuous women when seeking brief sexual
encounters; women are attracted to strong, broad-chested men of high status; application of
modus tollens is easier in contexts of social exchange than it is when reasoning about abstract
matters; people report disgust at the idea of incest; there is a higher incidence of violence

between children and their stepfathers than between children and their biological fathers, and so
on. These facts constitute the evidence that will support or disconfirm hypotheses about the
functions of psychological modules.
Because of the role behavioral evidence plays in a task analysis, it is also sometimes
possible to use this evidence to inspire a search for a psychological adaptation that one would not
have otherwise expected. This is especially clear in cases like phobias. People fear snakes,
darkness, closed spaces, heights, and storms. Evolutionary psychologists argue that these
phobias are too universal and too well-designed to be anything but the products of psychological
adaptations to particular selection pressures in the EEA. They wear their functions on their
sleeves. Similarly, one might wonder whether the Cinderella effect (Daly and Wilson 1998,
2005), in which a stepfather exhibits more violent behavior toward his stepchildren than to his
genetically related children, is an adaptation. Assuming that the Cinderella effect is real (this is
controversial: see Daly and Wilson 2001), one can begin to investigate evolutionary explanations
for it, relying on data about the effect to inspire hypotheses about the function of the module that
produces it, which in turn will generate predictions that will either support the functional
hypothesis at hand or suggest superior alternative hypotheses.
The idea of a task analysis of course pre-dates Darwin’s theory of evolution by natural
selection. Indeed, William Harvey’s discovery of the heart’s function, which also relied on a
task analysis, preceded publication of Darwin’s On the Origins of Species by almost 250 years.
This shows that one can make effective use of functional ideas without having to ground them in
natural selection. However, evolutionary psychologists argue that appreciation of the
evolutionary history of human psychology is essential for its explanation because the human
mind is equipped with adaptations that are not always adaptive in the current environment. The

modules that constitute human psychology had moved to fixation roughly by the end of the
Pleistocene epoch. This means that human psychology is adapted to an environment that did not
include agriculture, industry, or sophisticated technology. Failure to situate psychological traits
in the EEA will hamper our ability to explain them, preventing a proper understanding of what
they are supposed to do. A favorite example of this is the sweet tooth, which was once adaptive,
but in today’s world of Cinnabon and Ben and Jerry’s is now maladaptive.
3 Criticisms of Evolutionary Psychology
Evolutionary psychology has generated considerable heat, but it is important to
distinguish the personalities involved in these disputes from the tenability of the research
program itself. Some of the most prominent evolutionary psychologists have undoubtedly
ruffled feathers with grandiose claims about the revolution that evolutionary psychology
portends, and the new paradigm in psychology that it creates. Talk of paradigms cannot help but
invoke Thomas Kuhn’s notion of a paradigm, and evolutionary psychology clearly fails to meet
Kuhn’s criteria for a new paradigm. On the other side, some critics of evolutionary psychology
have used their positions of public celebrity to accuse evolutionary psychologists of very
fundamental misunderstandings of evolutionary theory – misunderstandings that properly trained
high school students would never make. Ultimately, the success of evolutionary psychology will
depend on its ability to establish the existence and illuminate the workings of the psychological
modules it proposes. There is presently some very compelling research toward this end, and one
must keep in mind that evolutionary psychology in its current form is only decades old. With
these caveats in place, it is time to consider some criticisms of evolutionary psychology.
Some critics have argued that claims about the EEA are untestable and so hypotheses
derived from speculation about the EEA are unscientific (Gould 1997). Others have argued that