Evolutionary Medicine
Miriam Nývltová Fišáková
Department of Physiology
Psychology and Behavior
• It is a truism that humans can be distinguished from other species, at least in degree,
by a large brain relative to body size. Our brain is characterized by a particularly welldeveloped
neocortex, and this feature has had a number of profound evolutionary
consequences. Our capacity to communicate, to use and develop technology, and even
the nature of the social structures we have evolved can be attributed to a large
neocortex. Humans are a social species. We evolved with characteristic behaviors adapted
to living in groups with other members of our species. Yet our societal structure has
undergone enormous changes in a few thousand years, from the small isolated clans of
foraging societies to the complex organizations of cities with populations of millions.
Increasingly, the social environment is changing in other ways. Family structure has
changed, and communication is no longer necessarily verbal and face to face; indeed,
telephone, radio, television, the internet, and social media are now all dominant forms of
communication.
• We considers how human behavior has evolved and how its evolution has influenced
behavioral morbidity, as reflected in a greater risk of some psychological and psychiatric
disorders. These forms of disorder are now a large component of the current and
anticipated burden of disease. The social environment is a major part of the selective
environment which has led to the evolution of our species. But at the same time, humans
have evolved with a rapidly changing capacity to alter their social and societal
environments. This capacity creates the potential for a mismatch between our evolved
phenotype and the environment we now inhabit. This mismatch, in turn, is likely to be a
potent source of psychological disorders.
Biological
Determinants
of Culture and
Behavior
• In everyday language, culture is usually understood as an
amalgamation of knowledge, behavior, and tradition within a particular
community or population. But creating a formal definition of “culture”
has itself been contentious. There have been intense debates among
social scientists over its precise definition, and some have argued that
culture must be viewed as a purely human characteristic. Modern
evolutionary scientists define culture as information acquired through
social learning. In this sense cultural phenomena may be observed in
other species, notably primates, cetaceans, and birds. It is obvious that
human culture evolves, and this cultural evolution is another form of an
inheritance system with the potential for both vertical and horizontal
transmission. Understanding the significance of the interplay between
biological and cultural evolution is important. The evolution of the
capacity to learn and the potential for learning to influence evolution
are also important components of evolutionary science. But what has to
be learned—and how it is learned—has changed dramatically and
rapidly in the past 12,000 years, from experiential learning within the
forager clan to the formalized and structured learning of modern
developed societies. Because of changing attitudes to what culture is
and how it originates, evolutionary explanations of human behavior
have had an especially contentious history. This contention arose in part
because of philosophical and political debate stemming from the ways
in which various disciplines have interpreted human behavior. Some
have wanted to view it as an entirely learned phenomenon, while others
argue that human behavior is built on some strongly selected and
therefore genetically determined components of brain function.
Extreme positions have been taken, or at least interpreted as been
taken, and at times the debate has been more polemical than critical.
The media have not infrequently exaggerated scientific reasoning and
observations into fatuous extrapolations of aspects of human behavior.
• We can reduce this discourse to the fundamental question of the
extent to which human behavior is determined (or influenced) by our
evolved biology. Several schools of thought have emerged to explain
the evolution of human behavior, largely based on how each school
conceived of culture, behavior, and learning. The debate was
distorted by the strong genetic determinism of late- twentiethcentury
biology. The distinguished evolutionary biologist and zoologist
E. O. Wilson, and subsequently many others including Richard
Dawkins, put forward strongly deterministic arguments in which all
aspects of behavior were essentially framed in genetic (i.e., evolved)
terms (Wilson 1975). Their critics, who included equally distinguished
evolutionary biologists such as Stephen Jay Gould and Richard
Lewontin, saw that this stance left little room for the role of active
decision- making, learning, and cultural adaptation. At its most
inappropriate extreme, some critics, particularly from the social
sciences and humanities, saw biological arguments being used to
excuse all forms of antisocial behaviors from rape to murder, a
position exploited by the media and which was a gross misuse of the
actual evolutionary theories. Social scientists take a very different
view from biological scientists: they see human behavior as being
produced by culture, learned from others. The basis of social science
is that humans are cultural organisms, and in general social scientists
perceive culture as a learned rather than innate phenomenon. They
argue that humans are quantitatively and qualitatively different from
other species in terms of the complexity of their culture. But culture
itself is a product of evolution and, as explained earlier, is not a
uniquely human characteristic. Learning can be demonstrated in many
animals. For example, some aspects of foraging are clearly learned,
feeding behaviors are culturally transmitted in some reptiles and
birds, migratory patterns are learned in some avian species, and tool
use in different groups of chimpanzees and New Caledonian crows is a
learned or culturally transmitted behavior. Some cetaceans have a
culturally transmitted whale song.
• Language provides a sophisticated capacity for communication,
and we have developed varied and complex social structures. Humans
are a prescient species, possessing consciousness; we use technology
in sophisticated ways, and we have developer belief systems
manifesting in religion and superstition. But there is an important
difference between the view that genes determine our behavior and
the argument that our evolved brain is the substrate on which
experience and the current environment shape our abilities and
behavior.
• A fair appraisal of the concepts would show that accepting
that there is a genetic basis to human behavior does not mean
that every aspect of human behavior is genetically determined.
Rather, as we have made clear throughout this book for other
systems, for neural function evolution has led to the selection
of inherited neural traits that provide a substrate on which
developmental and environmental influences (including the
social components of the environment) can act to mold
behavioral and neural phenotypes. Evolutionary biologists have
been particularly concerned with explaining how altruistic
behavior and the interplay between the sexes have emerged.
• We will extend the discussion to other aspects of human
behavior and psychology. Each of the various schools of thought
that have taken positions on the evolution of behavior can offer
valuable insights, and will draw from them to describe what, in
our view, is now a broadly held consensus on how evolutionary
principles can, and should, be used to explain human behavior
and psychology. In turn, evolutionary perspectives offer useful
insights for understanding certain psychiatric disorders.
Evolution of
the Human
Brain and
Behavior
• In considering the evolution of human behavior it is useful to bear in
mind the four questions suggested by the famous ethologist Nikolas
Tinbergen as a way of systematically understanding behavior (Tinbergen
1963). These are: what is the mechanism underpinning the behavior; what
is the function of the behavior; how does it develop during the life course;
and how does it evolve? Addressing each of these questions can help us to
understand behavior from both proximate and ultimate perspectives. The
ratio of brain size to body size in primates is about an order of magnitude
larger than that in other mammals. But even within the primate order,
humans and our ancestor species have had brain sizes that are
disproportionately large. The investment in a large brain has major
energetic considerations. The human brain consumes about 20% of the
body’s total energy but makes up only about 2% of bodyweight; the
proportion of energy consumed by the brain is considerably higher in
infancy. So a fundamental evolutionary question is why did primates, and
particularly hominins, evolve to invest so much of their energetic resources
in brain growth and function? The question does not have a single answer.
A simple answer is that the sensory and processing capacities of the brain
conferred adaptive advantages to the primate clade. For example, primates
use senses such as color vision to a greater extent than other mammals in
their search for ripe fruits. Evolutionary processes do not work on a single
trait in isolation, but operate on multipleinteracting traits. Indeed there has
been an interactive “ratchet” involving changing ecology, evolving social
structure, better communication, and better use of technology, all of which
have driven brain development.
• It is generally accepted that most adult humans operate with about
five levels of intentionality. Indeed, effective social discourse requires
this level of interaction to avoid unnecessary misunderstandings and
conflict. Clearly the higher the level of intentionality required, the more
likely it is that errors of interaction will result. Many problems in
interpersonal relationships, and even wars, have arisen as we employ
these higher levels of intentionality.
• Such advanced processing and engagement in social organization
clearly required, and was expedited by, the development of language.
• Once higher levels of intentionality had evolved, they provided the
capacity for further components of human culture to develop. They also
provided the basis for a high level of reciprocal altruism and detection of
cheaters, which have become fundamental to the structure of human
society. Higher levels of intentionality are required for the capacity to
have prescient self-awareness (including that of death), to develop
beliefs and superstitions (the forerunners of ritual and religion), to form
political structures, and to use language to communicate via the
complexities and beauty of literature. The theory of mind develops over
our life course. By the age of 4–5 years children can recognize a third
order of intentionality; before that they cannot lie convincingly. The
concept of a theory of the mind may be relevant to understanding
autism and the related Asperger’s syndrome (Baron-Cohen et al. 1997).
Those afflicted have a limited ability to interpret the intent of others,
suggesting that third-order and higher levels of intentionality have not
developer appropriately.
Evolution of
Social
Behavior
• Humans are characterized by living in groups larger than a family and, as discussed
previously, there is a compelling rationale for the view that we evolved living in clans of
about 100 to 150 individuals. Thus the social environment became a key part of our selective
environment, and selection would have favored traits that promoted fitness within that
environment. However, we also evolved in parallel with our cultural repertoire. There has
been a close link between our cultural evolution and our biological evolution, often referred
to as gene-culture coevolution. The development of consistent use of tools by H. habilis is
the first unequivocal evidence of culture in the hominin clade. Such tool-making capacity
eventually evolved through learning and cultural evolution into the technological repertoire
of modern society such as brain scanning, pharmaceutical development, nuclear weapons,
and the internet. There are many features of society which have undergone change, many of
which are self-evident. Over the past 10,000 years, virtually all human groups have changed
from being foragers living in small clans into pastoralists and city dwellers. These changes
have been accompanied by rising exposure to infection and malnutrition. The causes and
nature of trauma and conflict have also changed, with humans becoming their own main
predators, particularly through war and religious and other persecutions. There have also
been enormous changes in social structure. Organizational and thus power hierarchies
became necessary, and individual skills became differentiated: a surgeon and a lawyer
obviously have very different skills, and interpersonal interactions often now require higher
levels of intentionality.
Social Competition and Altruism
• One way that living with others influences our evolution is through social
selection. We discussed sexual selection—that is differential fitness created either
by competition between members of the same sex for the right to mate, or by
choice of mate by members of the opposite sex. Some authors have suggested that
sexual selection processes are a subset of social selection (West- Eberhard 1979),
the latter being a form of natural selection influenced by intraspecific social
competition or choice, in sexual as well as non- sexual contexts. We have discussed
the peacock’s tail as an example of a trait that evolved in the context of members of
the opposite sex choosing their mate. But consider the example of American coot
families, where offspring display highly ornamented and bright plumage to their
(gray) parents (Lyon and Montgomerie 2012).Attracting the parents’ attention is
crucial for provisioning food and so for offspring survival. We could say that sexual
selection involves fitness advantages relative to mating (and fertilization) while
nonsexual social selection influences components of fitness related to survival. Social
selection may have shaped aspects of human cooperation. Being selected as a social
partner would have enhanced survival for an individual of a species that lived in a
social group structure, particularly in environments where being an outcast would
put survival at risk. Thus there could have been selection of prosocial traits such as
empathy and altruism (Nesse 2007). One of the biggest challenges in evolutionary
biology has been to explain altruism, behavior that is apparently costly to the actor
and beneficial to the recipient, and which at first glance is at odds with the basic
tenet that selection operates on the individual. Initially altruism was used as an
argument for group selection, but problems were inherent in that concept and it
was largely abandoned. So if the unit of selection is the individual, how can behavior
that apparently does not serve the reproductive interests of the individual (i.e.,
altruism) evolve? Altruism is a common feature of mammalian groups. A meerkat
will take up a guard position to watch for a predatory raptor even though this entails
a greater risk of being spotted and becoming prey. One member, not necessarily a
parent, will guard the nest while others in the clan are out hunting. Much in human
social behavior appears to be for the benefit of others rather than oneself. As
discussed a favored explanation is provided in part by the concepts of kin selection
and inclusive fitness.
• William Hamilton, the originator of the concept of kin selection, argued that an animal would
behave altruistically with respect to other animals if they are likely to carry the same genes and thus
assist indirectly the intergenerational flow of some of its own genetic material (Hamilton 1964a, b).
This altruism would apply in the case of kin, and the closer the kinship the more likely it is that
altruistic behavior would be beneficial. This is formulated in Hamilton’s rule, which states that a
gene supporting altruistic behavior would be under positive selection whenever the benefit to the
recipient of the altruistic act (in terms of reproductive fitness) is greater than the cost to the
individual conducting the beneficial act. This benefit is clearly dependent on the degree of
relatedness: the greater the degree of relatedness the greater the benefit in terms of potential
gene flow. Indeed there is considerable empirical evidence that altruistic acts in animals are more
likely when there is a high degree of relatedness. This concept of kin selection has also been used to
explain the development of eusociality in insect species such as the honey bee. But the degree of
altruistic behavior shown towards kin may not just be determined by the degree of relatedness.
From an evolutionary perspective, aged individuals have less impact on inclusive fitness than those
of peak reproductive age. This consideration is termed reproductive value, and is a measure of an
individual’s potential to contribute to the gene pool of the lineage by virtue of their age. Generally,
having a larger social network and greater number of kin has positive effects on longevity. Several
studies have shown that underextreme conditions, such as the Donner Party disaster of 1847 where
US settlers caught in a snowstorm resorted to cannibalism, those with kin within the group were
more likely to survive as they were more likely to receive support from their relatives (Grayson
1990). Kin selection is an important component of human behavior. There is much evidence to
show, for example, that people are more willing to care for a relative’s child than for one who is
completely unrelated. We loan money to relatives on an entirely different basis from non- relatives.
The grandmother hypothesis, as a favored explanation for the evolution of menopause, can only be
understood in the framework of kin selection and inclusive fitness. In general, kin selection is
affected by age, as more altruism is shown to younger kin members, be it in patterns of childcare or
willingness to invest in medical care. In many species, such as the lion, males will kill the offspring of
another male when they are able to mate with the female who mothered those offspring, whereas
they will be protective of their own offspring. This may have a parallel in humans: Daly and Wilson
(1988) observed that step- fathers are more likely to abuse or murder step- children than are
biological fathers.
• It might be argued that the practice of adoption of unrelated children, common in the West today, is inconsistent
with concepts of kin selection (Volk 2011). Indeed in many traditional societies, adoption largely has a function in kin
support, with relatives (most often the maternal grandmother, in line with the evolutionary predictions based on kin
selection and paternal uncertainty) temporarily or permanently looking after the children of their impoverished or
deceased kin. This form of kin adoption is not uncommon today, though it usually takes the form of fostering or
guardianship, where ties with the biological parents are not severed. But while for the majority of adoptions in the
developer world, involving entirely unrelated individuals not necessarily from the same social or ethnic group as the
adopters, the explanation of kinship selection does not work, there may be other evolutionary explanations. One is
reciprocal altruism, with investment in non- related children generating opportunities for economic return in later
life. Another form of return is social. In some traditional societies adoptions are used to forge ties between groups or
rebuild damaged social relationships, similar to arranged marriages practiced, for example, historically in European
dynasties or still in many Asian societies. Finally, adoption may be a byproduct of powerful adaptations, for example
motivations to procreate and to parent, offering an outlet for such feelings to infertile couples. It is interesting that in
studies looking at the qualities in an adopted child that the prospective adoptive parents prefer, it has been found
that women emphasize cues of health (presumably because of their larger investment into care of offspring) while
males valued resemblance cues (presumably because paternity is far less certain than maternity). Adoption of
unrelated children (or surrogate pregnancies and egg donation without remuneration) is only one kind of example of
altruistic behavior extending beyond relatives. We give blood not only for psychological reward but in the expectation
that others will donate blood should we need a transfusion in the future. In forager communities, it is common for
food to be shared between unrelated individuals. This can be seen as a form of insurance against potential hard
times. The potlatches (festivals involving lavish gift- giving) of the Pacific Northwest peoples are an extreme example.
Such non- kin- based apparent altruism can also be demonstrated in animals. For example, the vampire bat will give
food (blood) to other unrelated bats in the colony that were unsuccessful in the hunt in expectation of the favor
being returned at a later date.
• The favored explanation for such behavior comes from another major
tool of evolutionary biology, namely game theory, and in particular the
concept of reciprocal altruism. The basic premise is that if A does a good
turn for B in the expectation that at some later time B will reciprocate by
doing a good turn for A, then both parties will benefit. However, this only
works if B is not a cheat (a “freeloader”): if B is a cheat, A has lost and B has
gained. Working with this simple model, game theorists such as the eminent
evolutionary biologist John Maynard Smith demonstrated that evolutionarily
stable strategies can emerge based on reciprocation and cooperation. These
strategies operate best where there is a great ability to detect and punish a
cheat. Indeed, many aspects of modern society are based on detecting
cheats and punishing them through ridicule, social isolation, or physical
punishment. A higher level of intentionality may allow more individuals to
try and cheat, but it also enables others to be better at detecting cheats. A
further argument for the origins and sustenance of altruism has analogies
with the handicap hypothesis or handicap principle. To be altruistic is to
demonstrate a generosity and richness that may be of value in the
competition for a social partner. If one can afford to give, it may be a signal
of wealth and quality, values that a potential mate may find attractive.
Indeed, in modern society we regard overt non-kin-based altruism
(manifested as bravery or philanthropy) as a particularly desirable
characteristic.
Selfishness and Selfish
Genes
• We have reviewed the evidence suggesting that humans
underwent positive selection for living in groups. It could be
postulated that the psychological mechanisms allowing
humans to live successfully in groups evolved because such
eusociality allowed the clan to solve problems collectively, but
this is not an argument for group selection. In this discussion it
is important to distinguish between selfish genes and selfish
behavior, a distinction often forgotten by the popular press
and some academics. The phrase “selfish gene” was simply a
catchy shorthand introduced by Richard Dawkins to emphasize
that evolutionary processes are fundamentally about
preserving gene flow, and that selection may well be acting at
the level of the gene rather than the whole. Kin selection,
natural selection, social selection, and sexual selection are all
manifestations of processes that attempt to preserve fitness
by protecting gene flow to the next generation, either directly
or indirectly. In contrast, selfish behavior is a description of an
individual’s behavior, but even here its interpretation depends
on the level of analysis. What may have had its origin in selfinterest
can lead to non-selfish behaviors that we interpret as
being altruistic. An example might be philanthropy, which
originates from the desire of the donor for social recognition.
• Emotions
• Emotions are universal human attributes and may exist because
they offered adaptive advantage in our evolution as a species.
Emotions do not occur in isolation, but involve integrated
physiological and behavioral responses to environmental stimuli,
either at the time or in recollection. Darwin recognized that the
physical manifestations of emotions can play a role in selective
processes, and he wrote an extensive volume on emotion (Darwin
1872). More recently, the evolutionary psychologists Leda Cosmides
and John Tooby, who developer a relatively extreme position
regarding the evolution of behavior, referred to emotions as the
“Darwinian algorithms of the mind,” emphasizing that these are
selected traits. Given their universality, emotions may have been
shaped by their adaptive value in signaling and responding to
situations that are frequently and universally encountered, such as
fear, panic, and sexual desire. In general emotions are healthy
phenomena. The challenge for medicine and psychology is when
emotions become situationally inappropriate in nature or severity
and impair the functioning of the individual.
Fear,
Anxiety, and
Response to
Threat
• Many aspects of our physiology defend us from external threats, and
some aspects of our emotions can be viewed as serving similar functions.
Fear and anxiety serve the obvious purpose of alerting us to danger and
maintaining a state of vigilance. They have evolved in response to threats
from predation and violence. Survival depends on the development of
sensory functions and prescient capacities to detect or predict threats from
other species. The development of a theory of mind allows us to understand
the intentions of other humans, and we need an ability to mount so-called
stress responses allowing us either to escape from predation or violence or
to fight back. There is an enormous overlap in the physiological responses to
threats of danger and to social stress. Humans rely on being members of a
group for their survival. Just as an isolated member of a herd species is at
particular risk of predation, an isolated human would have been at a
disadvantage in threat detection, in hunting and foraging, and in protecting
offspring. When placed in isolation, rats and many other species have a
marked endocrine stress response. Humans find social exclusion threatening
and stressful, as is evidenced by studies of prisoners in solitary confinement.
It is useful to distinguish between a stressor and stress itself. A stressor has
been defined as “a threat, real or implied, to the psychological or physical
integrity of an individual.” Detection of a stressor by an organism elicits a
coping strategy that may be an active (physical or behavioral) or passive
(psychological) stress response. Responses to stressors are usually short
term. However, the responses to chronic stressors may differ: the acute
stress response may become either exaggerated or attenuated, making the
effects of the sustained stressor more or less harmful. Either way,
pathological consequences arise when the coping strategy fails.
• Acute stress responses in complex organisms involve avoidance, withdrawal, or escape from the stressor, a change in central nervous
system function involving greater sensory awareness and alertness, stimulation of the sympathetic nervous system, and neuroendocrine
changes leading to activation of the hypothalamic– pituitary– adrenal (HPA) axis. Other hormones, such as growth hormone, which promotes
lipolysis, and vasopressin, which redistributes blood flow and affects kidney function, are also released by the hypothalamic– pituitary unit.
These stress responses are driven by the higher centers of the brain, from descending control by the frontal cortex (some people can become
just as stressed by being asked a question by a tutor that they cannot answer as others are when physically attacked; the Trier test is a stress
test used in behavioral and endocrine studies that is simply a test of public speaking). The limbic system coordinates the response and plays a
role in mediating the potentiating or inhibiting effects of chronic stress. The HPA axis has built- in mechanisms for feedback control mediated by
glucocorticoid receptors at various levels of the axis, with the hippocampus being a major site of feedback. Hence, changes in the expression of
glucocorticoid receptors during development or during chronic stress can alter the magnitude of the response. In turn, activation of the HPA
axis and catecholamine release induce metabolic changes, including glycogenolysis and gluconeogenesis to provide energy resources for “fight
or flight” responses and cardiovascular responses that increase heart rate and blood pressure and redistribute blood flow. Chronic stress
responses include further neural changes: for example, elevated glucocorticoid levels can change mood and affect memory and induce a wide
variety of secondary physiological changes, many induced by chronic hypercortisolemia. Exposure to chronic stress in early life has been
associated with later risk of depression.
• Changes in the physical, biotic, or social environment can
all act as stressors. These conditions offer different challenges,
yet the response is stereotypical.
• The stereotypy suggests that the stress response originally
evolved to deal with one set of conditions, for example threat
from a predator, but then became co- opted and selected as an
advantageous response to another set of conditions (i.e., it is
an exaptation). An Olympic athlete poised to sprint at the start
of a race shows many of the same physiological responses as a
rabbit that sees a fox or a swimmer who faces a shark. The
stereotypical nature of the response is fail- safe, in that it
heightens awareness of a situation in which threats may arise,
even if they have not yet done so. This is akin to the “smoke
detector principle”: false alarms are better than failing to react,
so selection may have favored the response being set on the
“sensitive” side (Nesse 2001). Anxiety allows us to acknowledge
current threats and anticipate and avoid potential threats.
These clearly have an adaptive origin, but if expressed
inappropriately can manifest in an inappropriate form as the
psychiatric disorders of anxiety and phobia. More severely
threatening life experiences may manifest as post-traumatic
stress disorder.
Love, Jealousy, Marriage, and Inheritance
• Given the centrality of reproduction to evolutionary biology,
much research in evolutionary psychology has focused on human
behavior in relation to mate selection, pair bonding, sexually selected
traits, familial investment strategies, the role of each gender in
society, and the nature of male–female relationships. Again it is
important to recognize that whereas we will focus on evolutionary
determinants here, humans will overaly other cultural behaviors on
top of these evolutionarily determined fundamentals. Strictly from the
point of view of evolutionary biology, the pattern of interaction
between parents of sexually reproducing species has evolved to
maximize the fitness of their offspring. Where they can, females
choose their mate in the expectation that the mate will be able to
contribute to her fitness by supporting the nurture of their offspring.
This is true for both polygynous and monogamous mating structures.
Sexual selection has operated to favor females with those
characteristics most likely to support successful pregnancies. Pair
bonding helps reinforce this interaction, and romantic love may be a
mechanism that evolved to help reinforce this bonding. Equally,
jealousy can be envisaged as a response to the breaking of these pair
bonds. The long nurturing period required for human offspring and
the nature of human culture means that humans can continue
throughout life to affect the potential fitness of their offspring.
Complex social arrangements have emerged to enable them to do so.
Again, from an evolutionary perspective, the concepts of property
inheritance, marriage, dowry, and so forth are all mechanisms to
protect the status and wealth of offspring in an attempt to promote
their reproductive success. Different societies have developed
complex rules of inheritance and marriage systems, and these can
often be understood in terms of the ecology of a particular society.
For example, in many societies male reproductive success is linked to
wealth and a father’s inclusive fitness might be greater if he
concentrated his wealth in the hands of fewer of his male offspring
rather than benefit them evenly. This is seen in some pastoralist
societies where large herds of cattle are more viable than smaller
ones, and thus spreading cattle evenly might reproductively
disadvantage all of a man’s sons. In such societies reproductive
success is generally greater for older brothers than for younger ones.
There are echoes of this approach seen in primogeniture (where the
first-born son inherits all), which has been practiced in some European
societies.
• Parenthetically, the economic historian Gregory Clark believes
that primogeniture helps to explain why the Industrial Revolution
occurred initially in England: it created a population of well-educated
but impoverished younger sons who sought status through trade and
innovation (Clark 2009).
Group Behavior and Morality
• Animals living in groups have a set of behaviors that are necessary for harmony within the group. In some species, such as the
hyena and wolf, this involves an obvious hierarchy within the group, with clear roles and rights for the alpha male or female.
Humpback whales hunt fish together in the phenomenon known as bubble net feeding, and fish school because it reduces the risk of
any individual member being eaten. Humans live within a particularly pronounced group structure. This group structure evolved
because it provided a fitness advantage for its individuals, probably for cooperative food gathering and defense against predators or
rival groups. Highly social species exhibit a number of behaviors that reinforce group bonds, such as grooming in the chimpanzee and
sexual stimulation in the bonobo. It was suggested that the evolution of language and gossip played a major role in generating and
stabilizing bonds within early human groups. As group living requires multiple behaviors and is an integrated phenotype, all these
selective pressures would have acted to determine the social and behavioral phenotype of our species. Natural selection, unlike
artificial selection, does not act on any one trait in isolation. Therefore, teasing apart and arguing for greater weight for one
component or another is neither practical nor sensible. But as we have already suggested, membership of a well-bonded social group
requires adherence to the rules of reciprocity. Human groups are particularly sensitive to freeloaders or cheaters. We respond to
cheating behavior with exposure, ridicule, embarrassment, and punishment. Frameworks of what behaviors are acceptable or
unacceptable become formalized within the group. As group size becomes greater than about 150, a formal internal structure is
required for stability. Concepts of morality may be derived in part from these context-specific frameworks necessary to control
freeloaders. They may be manifest in custom, aboos, rules, and tradition. But other factors also play an important role in a particular
societal view of morality. These include rules and concepts imposed in part by hierarchical organizations to protect the social
structure, and in part by the formalization of belief systems.
Belief and Religion
• Every human society is characterized by one or more belief systems that are
reflected in its organization, tradition, and ritual. These belief systems generally
involve some concept of the supernatural. Ritual burial implies a sense of
afterlife and has existed for at least 70,000 years. Belief in the supernatural was
almost universal until modern rationalism emerged. The issue of why and how
belief in the supernatural arose has been the subject of considerable
evolutionary reflection since the initial musings of Freud (Boyer 2001;
Norenzayan 2013). The evolutionary question is whether belief in the
supernatural has an adaptive advantage or is simply an epiphenomenon related
to other group behaviors. Supernatural belief is counter-factual and the
adaptive advantage of suspending reality is not entirely clear. Its origin is also
highly controversial. Perhaps it allowed individuals and the groups they were
members of to develop an emotional stability in the face of events (such as
drought) that they could not comprehend or predict. Ritual, which often
accompanies superstition, helps build group cohesion. Sagas and story-telling
are often part of a belief system, and these may have helped reinforce group
identity and thus cohesion. In addition, belief in the supernatural as a potential
external source of punishment or reward could help a group deal with the
problem of freeloaders. The 30,000-year-old wall paintings in the caves of
France and Spain may well be some of the earliest representations of ritual and
belief, though other explanations are possible. The organization of belief into
formalized religion from perhaps 5000 years ago occurred in parallel with the
development of larger population groups and the associated political
organization.
On the Origin of Art
• The existence of “art” across human societies throughout history has puzzled
scholars for a long time. Stylized etchings on bone and stone dating back at least
70,000 years have been found in southern Africa. Representational art dates from
at least 32,000 years ago, in the cave paintings of Western Europe, and perhaps
even longer ago in the rock art of Australia. Indeed evidence of art can be found in
all human societies, from the Australian Aboriginal painters to the audience
attending the Metropolitan Opera House in New York or the graffiti on a subway
station wall. Though some critics deny its universality, arguing that it is Western
culture that has invented art as we know it, the same major forms appear
everywhere in the world: music, dance, visual arts, and storytelling. Art does not
appear to require formal training in the way that, for example, reading does; it is
sustained despite its costs; and it provokes a strong emotional response.
Explanations of art include those that ascribe certain functions to it— for instance
as means of communication or expression— but such explanations beg the
question of why art would survive alongside other, less costly, means of
communication and expression. The ubiquity and antikvity of art have stimulated
questions about its biological origin. Darwin thought that the “high cost, apparent
uselessness, and manifest beauty” indicated the origin of a trait/ behavior in sexual
selection (Darwin 1871). Dance, for instance, often occurs in mating rituals. But
sexual selection can only account for some aspects of art. Drawing on a large body
of evolutionary and humanities literature, the literary scholar Brian Boyd has
explained the evolutionary origin of art in play (Boyd 2009). Play, which is widely
found among animals and is an essential part of human early development, is
understood as a way to develop, finetune, and practice mental, physical, and social
skills within a safe context. Art is an advanced form of cognitive play that builds on
several aspects that are unique or especially evolved in humans. One is the
preference for patterned information. Humans search for patterns— discernible
order in things, actions, and situations— in order to understand the underlying
rules, to make inferences, and thus make predictions. Musical motifs, visual
themes, storylines, can all be understood as patterns with which the human mind
engages and plays. But art could not evolve without the shared attention and
sociality characteristic of humans: think of chanting, dance, body adornment; of
traditional styles of pottery and woodcarving; or indeed of folk poems and
storytelling traditions. The intense emotional response provoked by art might make
it more effective than other forms of communication and expression. Indeed, art
fosters intense group cohesion: an example would be sports teams (and their
audiences) singing national anthems before international games. These properties
of art can explain why art, in various forms, was extensively used by religion: who
can separate Christianity from the soaring, highly decorated forms of Gothic
cathedrals or spectacular visual representations of the textual tradition, for
instance Michelangelo’s paintings on the ceiling of the Sistine Chapel.
• David Sloane Wilson and others have suggested that organized
religion became a major way to control freeloaders and stabilize a
large group (Wilson 2002). Some have argued that organized religion
largely developed as a political tool within a hierarchical control
system. Many societies have conflated political rule and concepts of
deity. Until the seventeenth century, British monarchs were
considered to have divine powers of healing, and today they are still
nominally head of an organized religious structure. A common
hypothesis is that religion evolved as a way of confronting the
problem of inevitable death, and that complying with the group’s
behavior would hopefully lead to a deferred reward. But Wilson also
suggested that the religious group needs signs of commitment from
an individual if they are to receive the rewards of group membership.
This could take the form of sacrifices, tithes, or changed behavior
(e.g., not eating meat on specific days). Paying a price to be a
member of a group reduces the risk of someone being a freeloader.
The risk of being involved in cheating is not only exclusion from the
group but also punishment by some higher authority such as deity or
supernatural force. Wilson developed this hypothesis to argue that
religion evolved through a group- selection process. His position
remains controversial, and this discussion, alongside related ones,
plays a considerable part in the framing of multilevel selectionist
arguments. Those who would focus on individual-level selection and
reject any concepts of group-level selection would argue that the
adaptive value of reciprocal altruistic behavior and group living for an
individual provides a sufficient evolutionary explanation. Within the
context of the parallel processes of biological and cultural evolution,
ritual and religion can be seen to have adaptive advantage for the
individual and a group selection argument is not necessary.
Learning
• Humans are born in a relatively immature neurological state compared with other primates. Nevertheless, the
human infant is not born with a total inability to perceive or react to its world, and is certainly not as immature as
more altricial species such as the rat. Much experimental and clinical data now show that human babies have very
active sensory processes. They prefer symmetrical objects and images of an organized (rather than a scrambled) face.
Their sense of smell has also developer to the point that they can identify the smell of their mother. By the age of 9
months, babies are clearly able to recognize and respond to the psychological state of others, and by 15 months they
can persuade their mother to react by pointing to an object. Learning then becomes a process of acquiring skills and
changes induced through interactions with adults, which leads to new skills. Humans have evolved “goal-based”
imitative learning, which allows the growing child to learn about the goal and the actions necessary to reach it.
Gradually this permits children to engage in their culture, and this process is greatly accelerated by the acquisition of
language. By the age of 4 years children have moved to a level of cognitive development for which at least secondlevel
intentionality can be demonstrated. Learning from experience is a key adaptive capacity of many species, but is
particularly well developed in humans. Learning by forming associations between events, called associative learning,
is present even in children and is a necessary precursor to inferential reasoning. The capacity to learn is regarded by
some as simply another module of them mind in the context of orthodox evolutionary psychology. Others regard it as
flexible and generic, rather than domain specific. Again, we see this argument as unnecessary in the context of this
book. Humans have evolved with a brain capable of assessing environmental information, storing information as
memories, and thus guiding decisions and consequent behavior. Rather than trying to encode all possible responses in
our genes, selection has endowed us with an advanced organic “computer” that can learn by association and
experience, and make appropriate decisions. Indeed, in developmental learning, experience reinforces particular
synaptic pathways and neuronal networks. Human learning is effectively a process of reinforcement by positive
outcomes and avoidance following negative outcomes. Thus we learn to seek ripe fruits, but not to eat toadstools.
Evolutionary Perspectives on Psychology
• We have highlighted how many aspects of human behavior can
be better understood by including evolutionary as well as cultural
perspectives. In doing this we have taken an integrated perspective,
namely to examine to what extent a behavior can be considered to
advance or protect fitness. The field of evolutionary psychology has
also considered how the mind itself evolved. There are marked
similarities between this discussion and considerations of how
language evolved. Several schools of thought, based in part on
different conceptual approaches, have emerged. Whereas the term
“evolutionary psychology” can be used narrowly to describe a single
one of these schools (that founded by Leda Cosmides and John
Tooby), we will use it here in its broadest and most inclusive sense.
Two extreme views exist: first, that the brain is a universal tool able to
respond flexibly to a variety of situations, and alternatively that the
brain has evolved as a series of domain-specific modules. The most
prominent advocates of the modular view, the evolutionary
psychologists Cosmides and Tooby, proposed that there were strong
selection pressures for each capacity of the mind to have evolved as
an independent module (Barkow et al. 1992). There were perhaps
thousands of modules, each for a different behavior; for example a
module to detect freeloaders, a module to learn language, and so
forth. A key concept in their thinking was that of the environment of
evolutionary adaptedness (EEA). This was the putative environment
that existed through the bulk of human existence, at least until the
end of the Neolithic, during which selective pressures acted on human
physiology and behavior to lead to the current portfolio of human
behaviors. The modular model implies that behaviors have an
adaptive origin and must largely be genetically determined. One
limitation of the concept of EEA is that there was in fact no single
EEA—rather a large number of different environments in which
Paleolithic humans lived (Foley 1995).
In contrast, the opposing model would suggest that most behaviors are learned, but can only be learned because of the evolved neural substrate. This dichotomy is an exaggeration made by
advocates of particular schools of thought in order to make specific points, and is to some extent unnecessary. What is clear is that humans have evolved with a neural infrastructure that is
capable of learning, and with a series of cognitive abilities able to cope with novel situations and living within a complex social organization. But there is some stereotypy in a number of
behaviors and emotions, and evidence for genetic determinants suggests that a finer grain of selection has operated. There is a renewed interest in the role of genetic assimilation as a
process by which learned behaviors are converted into genetically based behaviors. Indeed, the first description of what we now term genetic assimilation was called the Baldwin effect after
the psychologist James Baldwin who was one of the first theorists to describe how behavior might affect evolution (Bateson and Gluckman 2011). Despite its limitations, the modular model
does emphasize an important point. The human brain evolved under very different social and macro-environmental conditions from those in which humans now commonly live. If these
modules were based on appropriate psychological adaptations when they evolved, then there will now be a mismatch between those modules and the modern constructed world. There will
therefore be situations where the adaptations that underlie human behaviors have lost their adaptive advantage, and may instead become manifest as maladaptive pathologies. This
argument has echoes of that used to describe the evolutionary origins of metabolic disease. Key to this school of thought has been the understanding of how the original selective
circumstances led to a particular module of behavior being selected. For example, a module for fear of dangerous animals such as snakes could be envisaged. Jealousy could also be
conceived as a module that had an adaptive advantage, as a jealous individual was more likely to have a selective advantage over someone who took a passive view of being the victim of
infidelity.
In the arguments over the origins of language, linguistic researchers view universals, patterns that appear in all natural languages, as having a selected origin. The debate among linguists on
this issue has been extensive and somewhat vexed, and the evidence for universals is not compelling. Similarly, there are obvious universals manifest in the human emotions, in the patterns
of infant development, and in many aspects of social interactions such as mate choice and avoidance of incest. These can be taken as evidence for an evolved mind. While there is
considerable merit in this approach, the caveats are equally valid here. Certainly, not all aspects of human biology need have an adaptive origin. There is a danger of falling into the trap of
“just-so stories,” since spandrels and exaptations may apply equally to neural functions as they do to other aspects of biology. For example, while jealousy has been suggested to have an
adaptive origin, there are no data to suggest it has a genetic basis and it might merely be the by-product of other capacities of the brain. Obviously there are limits to the empirical proof that
is possible in evolutionary psychology, although the science is no less important for this.
Baldwin effect
Evolutionary
Psychiatry
• The application of evolutionary principles to psychiatry builds on
the previous discussion. The various schools of evolutionary
psychology have given rise to diverse views on psychiatric states.
Because mental health disorders such as depression and anxiety are
particularly common, affecting perhaps 25% of the Western
population, it is necessary to consider why the evolved brain is
vulnerable in the modern world. Some psychopathologies occur at
high frequency and cannot be explained by single causes such as a
monogenic trait. In these cases, the origin of syndromes such as
affective disorders may be due to a discrepancy between our evolved
biology and the current environment, resulting in maladaptive
consequences of a selected (adapted) trait. The key issue is the
capacity to adapt to conditions that require a particular behavior. As
with metabolic physiology, there are a range of psychological
responses that can be called upon to deal with a particular situation.
Just as metabolic disease can develop when individuals live in
environments with an energetic load beyond their selected capacity to
cope, psychological systems can be limited in their capacity to adapt.
These limitations may then be revealed in different societal or social
conditions. The limits of this plasticity are genetically and thus
evolutionarily determined. It is important to note that, irrespective of
the conceptual model being used, specific genes do not link to specific
behaviors but rather to the functional neural networks that are
involved. However, this does not mean that there are no associations
between SNPs and some psychiatric disease—recent work has
identified two SNPs associated with major depressive disorder in a
population of Chinese women (CONVERGE Consortium 2015). The
debate between different schools of evolutionary psychology is
essentially over the extent to which the brain remains plastic and the
extent to which it is constrained in its plasticity by genetic
determinants.
Personality
Traits and
Disorders
• Personality traits can be defined as particular and somewhat inflexible ways
of behaving. Individuals are recognized as having quite different personalities,
and indeed we can recognize distinct personalities in domestic pets and in wellstudied
colonies of wild primates. One view of personality traits is that they
represent constrained plasticity within the behavioral system. In general,
evolutionary psychiatry assumes that a number of personality traits may have
originated through adaptive advantage, but have become maladaptive in the
current context. For example, a paranoid or anxious tendency may have
originated from an evolved and fitness-enhancing trait that helped avoid
predators. Risk-taking behavior may have been a trait that was advantageous in
finding both a mate and new food supplies. When a personality trait is
particularly exaggerated or constrained, it is considered pathological and is
termed a personality disorder. Evidence from twin studies (despite their
limitations) shows that even when reared apart, monozygotic twins exhibit
concordance for a number of personality traits (Tellegen et al. 1988). This may
reflect evidence of genetic determinants. In evolutionary terms, individuals with
antisocial personality disorder can be viewed as a manifestation of the
cheater/freeloader. These individuals, whose personality often emerges in
adolescence, are characterized by behaviors representing their willingness to
take from the group without reciprocation. Game theory explains how cheaters
can persist in a society made up primarily of reciprocators, and this theory
suggests that if they reproduce their genes will persist even if societies attempt
to exclude them. A key feature of antisocial behavior is the extent to which
deception is used to hide it. It is inevitable that some cheaters will persist in any
population.
• It is important to distinguish this type of behavior from the acting-out behaviors of adolescence. Such
behaviors are transitional and arise because physical maturation precedes complete psychosocial
maturation. Thus, adolescent acting-out behaviors occur during a period in the life cycle when there may be
additional value in showing exploratory and risk-taking behavior as a form of reproductive display. Indeed,
males show a persistent tendency towards risk-taking behavior throughout life. Many individuals can be
seen as pushy and attention-seeking, or as impulsive or aggressive. Again, such behaviors could be seen to
have had adaptive value in the mating game. There are individuals who have difficulties in maintaining
interpersonal relationships and have a poor self-image. As a result they may have a tendency towards
suicidal or other self-damaging behaviors, inappropriate temper, and chronic feelings of emptiness. These
individuals are unable to adapt to their social circumstance, often because they have a lack of insight or a
limited capacity to interpret the circumstances they are in. This manifests as a pathology known as
borderline personality disorder. Affected individuals are constrained in their ability to participate in their
group and their behaviors can be perceived as unsuccessful attempts to be integrated and accepted as
active members of the group. The recognition that they are unsuccessful can lead to overt efforts to exit the
group. Narcissism is defined by a need for admiration, and is generally associated with a lack of empathy for
others. Narcissists often have great difficulty in a social environment and in maintaining relationships, and
are highly sensitive to criticism. Again their behaviors could be viewed as an exaggerated attempt to
socialize despite limitations in their capacity to do so.
Disorders of Mood
• Emotions are the result of the brain evolving ways of controlling physiology and behavior for advantage in particular
situations. A feature of human behavior is the pursuit of individual goals which, in turn, can be mapped back to their potential
fitness advantages. For example, controlling more material resources is likely to have been advantageous for a male when seeking
a mate. Humans experience a wide range of emotions in the course of pursuing their social and physical goals. These emotions are
part of the equipment necessary for achieving these fitness-related goals and coping with any challenges encountered in doing so.
However, inappropriate or exaggerated emotions are maladaptive and can become pathological. This can occur because the
substrate is abnormal [e.g., a polymorphism at the promoter region of the 5-hydroxytryptamine serotonin-transporter (5-HTT)
gene has been associated with emotional disorders (Lesch et al. 1996)], or because the social environment exceeds the
individual’s capacity to adapt emotionally. As we have discussed, there is a compelling argument that humans are not evolved to
live in a “concrete jungle” with an enormous and broad level of interpersonal interaction. The constructs of hierarchy, family
structure, and individual role are now very different from those that existed even five generations ago in Western society, and
even more so from those that existed prior to agriculture and settlement. This dramatic change in social environment may have
exceeded the capacity of some people to adjust, and the consequences are emotional disorders such as anxiety and depression.
Anxiety
There is ample empirical evidence that anxiety can have adaptive value. Within a school, timid fish are more likely than bold fish to survive a predator. Anxiety is a
way of being alerted to potential danger, but, even so, no individual can sustain a state of maximum alertness all the time. Anxiety has an energetic cost resulting
from physiological changes such as sweating and increased metabolic rate (the effects of catecholamine release), blood pressure, and heart rate. As discussed
above, chronic stress and chronic anxiety states are very similar, so, not surprisingly, both are maladaptive and can have deleterious effects on the individual.
Phobias
Phobias may represent exaggerated forms of what would otherwise be healthy, adaptive responses that enhanced survival in their original form. Most phobias arise
from situations of perceived danger from attack, predation, or trauma. Agoraphobia and claustrophobia can be interpreted as originating from fear of exposure to
attack or inability to escape. Transient phobias are normal, and fear is an important part of learning what to be afraid of. Failure to be fearful would have been a
selective disadvantage, and it has been pointed out that the costs of an exaggerated fear response are less than the costs of not being fearful and being eaten! A
psychological disturbance arises when there is loss of the capacity to distinguish between legitimate causes of fear and responding inappropriately to innocent
stimuli. In the latter case, the psychological responses become maladaptive because they inhibit the capacity of the individual to function in society. Thus phobias
can be seen as having a hypersensitive “smoke detector” function and this understanding has proved valuable in developing therapeutic approaches (Nesse 2001).
Depression
• Happiness and sadness are universal human emotions, and changes in mood are a normal part of the life course.
Sadness is a normal response to a fitness-impairing event such as loss of a child, a spouse, material resources, or injury to
the group in which the individual lives. Sadness may be a way of becoming transiently demotivated, thus helping the
individual to avoid making decisions under stressed conditions that might be maladaptive in the long run. Being sad may
lead the individual to stop a behavior that had caused an initial loss, and promote a period of self-reflection. It may induce a
pause and a period of rethinking that could rebuild a threatened pair-bond relationship or change a hunting strategy that
had led to the loss of a group member. It may stop the individual confronting a more powerful member of the group
following loss of power or status, a situation likely to lead to an adverse and perhaps fatal outcome. Equally, sadness may
be a way of communicating within a group the need for support from other group members. It is argued that the emotion
of sadness emerged to act as a brake on some behaviors, and happiness as a way of promoting others. Essentially, they are
tools for changing the responsiveness of an individual to a particular situation and communicating with others in the group.
While these emotions may have evolved in such a manner, they have been incorporated into other components of our
existence. Inappropriate extremes of mood are reflected in pathological depression or hypomania. The socioeconomic
gradient in health is well recognized.
• A major part of our construct as a social species involves hierarchy and control. Loss of esteem, reputation, or power
induces depression. This can be seen as a response to reduced status in the battle of sexual or social selection, and as a
consequent form of submissiveness. It may allow the individual to survive to reproduce rather than being killed or expelled
from the group. There is ample evidence that individuals who are disempowered or at the bottom of hierarchies are more
stressed, and have more emotional disorders and physical illnesses.
Psychoses
• Hallucinations, paranoia, detachment from reality, and withdrawal are symptoms of
psychoses, and in particular the schizophrenia syndromes, which affect about 1% of all
populations. Generally, schizophrenics behave as if they are living in a different world
from others in their social group. Developmental and genetic factors both appear to play
a role. People with schizophrenia are characterized by having deficiencies in their ability
to exhibit higher orders of intentionality, and there are data to suggest that early life
factors may have disturbed the normal development of their neocortex. For example,
there is an increase in the incidence of schizophrenia in offspring whose mothers
experienced famine when pregnant or were exposed to viral infection during pregnancy
(Susser and Lin 1992). This finding suggests that there can be developmental constraints
imposed on behavior which are later exposed as psychopathology in some individuals.
There are also data showing that those born small are more likely to develop depressive
disorders. However, it is well recognized that there are also genetic determinants of
schizophrenia, and when a common disease with genetic determinants persists at a
steady proportion in a population the question of whether there has been a selective
heterozygote advantage will arise. That schizophrenia may be a result of balancing
selection was first proposed as early as the 1960s by such leading theorists of
evolutionary biology as Julian Huxley and Ernst Mayr (De Bont 2010). But the selective
advantage of schizophrenia has remained elusive, the most popular proposals being
(without any compelling evidence) enhanced creativity and novelty seeking. The role of
schizophrenic and drug-induced hallucinations in the origin of belief in the supernatural
and religion is an equally fertile ground for wild speculation. Most recently the origin of
schizophrenia has been explained using the “imprinted brain” hypothesis (Crespi and
Badcock 2008). This hypothesis relies on the concept of genetic conflict and the
phenomenon of imprinting arguing that, because the father of a child may not father
the mother’s later children, it is in his interest to maximize the child’s growth even at
the expense of maternal health and future reproductive success. The mother, by
contrast, would do better to limit the investment in the child to preserve some
resources for future (and possibly existing) children. As a result, genomic imprinting with
a maternal bias would arguably lead to a smaller child, more tractable behavior, and in
its extreme form, schizophrenia. By contrast, a paternal bias would lead to a large child,
willful behavior, and, in the extreme form, risk of autism spectrum disorder. This theory
has possibly received some support from Danish health registry data that indicated that
babies of above average size had a significantly higher risk for autism spectrum disorder
and a lower risk for schizophrenia, while babies below average size had a lower risk for
autism spectrum disorder and a higher risk for schizophrenia (Byars et al. 2014). The
increase in risk, however, appears small, and it is also not clear if there other causal
factors at play: for instance, while for schizophrenia the relative risk decreased from the
smallest birth weight towards larger, in the case of autism spectrum disorder the curve
appeared almost U-shaped, with small babies (under 2500 g) having a similar relative
risk to babies weighing 4500 g. This remains a field full of speculation, with some
association studies but no compelling conclusions possible at the moment.
Key Points
• • Human behavior is built on selected, and therefore genetically determined, components of brain function.
• • The evolved brain is the substrate on which individual experience and the current environment shape abilities and behavior,
giving humans the flexibility to exist in a wide range of societal environments.
• • Humans are social animals characterized by living in groups larger than their immediate family. Selection has favored traits that
promoted fitness within this environment, such as cooperation, reciprocal altruism, and the abilities to interpret the actions of other
members of our species and to detect freeloaders.
• • Emotions have adaptive value for a social species, but they can become maladaptive with consequences for psychological and
psychiatric well-being.
• • Such maladaptations may have arisen because of changes in the human social environment, or because of
genetic/developmental factors creating functional variation in pathways determining behavior.
Thank you for your Attention!