Empirical testing of evolutionary hypotheses has used to test many theories both
directly and indirectly.
Why do empirical testing?
In fact, the general theory of evolution has been accepted as more or less true.
Below the general theory are “middle” level theories such as parental investment
and sexual selection. For example, women bear the burden of nine months of
gestation and, in a sense, have a different kind of “parental investment”.
Evolutionary psychologist predict and the test the hypotheses, based on their
investment, that women will choose mates who are willing to invest resources in
them and their children and will divorce men who fail to provide these resources.
This approach is called a deductive reasoning approach. The researcher develops
theories and goes about engaging in hypothesis test and data collection to develop
or support that theory. This is also called top down empirical research.
In contrast to this approach, the inductive reasoning approach starts with
observations and builds theory from this. This is also called bottom up empirical
research.
In either approach, accurate predictions made by theory can help to support that
theory telling researchers that they are on the right track while inaccurate
predictions call the theory into question.
From the evolutionary perspective, three main areas of interest have generated some
interesting and illuminating findings. These areas are:
 human nature
 sex differences
 individual differences
Human nature has always been at the very core of more of the grand theories of
psychology.
 Freud – sex and aggression
 Adler – striving for superiority
 Skinner – domain general learning mechanisms
 Robert Hogan – the desire for status and acceptance by the group (a grand
theory?)
From this perspective, human nature is the primary product of the evolutionary
process. Psychological mechanisms that are successful in helping humans survive
and reproduce tend to out-replicate those that are less successful. These
mechanisms are also the mechanisms that make humans different from mammals
and other lower species.
Need to Belong
Hogan argues that the most basic human motivators are status and acceptance by
the group. The most important social problems early humans had to solve in order
to survive and reproduce involved establishing cooperative relations with other
members of the group and negotiating hierarchies. Achieving status and popularity
likely conferred a host of reproductively relevant resources on an individual,
including better protection, more food, and desirable mates.
Being ostracized from a group was extremely damaging. It may have been the
stimulus for the development of social anxiety which is the distress or worry about
being negatively evaluated in interpersonal situations.
Researchers wanted to see what behaviors elicit social anxiety to see if these had
some evolutionary consequences. Some of these behaviors include:
 cowardice in the face of danger
 displaying aggression toward in-group members
 trying to lure away the mates of in-group members
 stealing from in-group members
 murdering in-group members
Do the data support this hypothesis?
Empirical evidence supports the contention that the need to belong is a central
motive.
 Groups share info, food, and other resources (increase resources results in
increase in group cohesion – radio)
 Groups offer protection from external threats and defense against rival
groups (WWII)
 Groups contain concentrations of mates needed for reproduction
 Groups provide the opportunity to receive altruism and invest in genetic
relatives
Altruism is a direct function of the recipients’ ability to enhance the inclusive
fitness of the helpers. As the degree of relatedness decrease so should the level of
altruism or helping. The data support this hypothesis.
This varies with the context (life or death vs. everyday situations), with age (youth
> elderly), with trivial helping (old > youth), and with famine situations (youth >
elderly). Keep in mind the reproductive capacity of the individual. Youth have a
greater potential than elderly individuals.
Universal Emotions
Are facial expressions interpreted the same ways across cultures? This might
represent universal criteria of adaptation. Or, if all humans share an adaptation, like
smiling to express happiness, that adaptation is likely to be a core part of human
nature.
Or, fitness affordances suggest that emotions guide the person toward goals that
have conferred fitness in ancestral environments or that would avoid conditions that
interfere with fitness.
Or that a “manipulation hypothesis” might suggest that emotions are designed to
exploit the psychological mechanisms of other people.
Research has demonstrated that seven different emotions including; happiness,
disgust, anger, fear, surprise, sadness, and contempt are recognized nearly
universally!
Emotion may be a “central component” of personality.
Sex Differences
Evolutionary psychology predicts that males and females will the same or similar in
all the domains in which the sexes have faced the same or similar adaptive
problems. It predicts that, in other domains, men and women have faced
substantially different adaptive problems over human evolution and, in these
domains men and women will be different.
For example, women face childbirth while men do not.
There may be differences in information processing between men and women as
between paternity and maternity.
Women have faced the need to find and replenish their food and supplies, especially
for their off-spring.
Evolutionary-predicted sex differences holds that the sexes will differ in precisely
those domains where women and men have faced different sorts of adaptive
problems. Men and women are psychologically different.
 What domains have men and women faced different adaptive problems?
 What are the sex-differentiated psychological mechanisms of women and
men that have evolved in response to these sex-differentiated adaptive
problems?
 Which social, cultural, and contextual inputs affect the magnitude of
expressed differences?
These include differences in aggression, jealousy, desire for sexual activity, and
mate preference.
Aggression
 Males have a propensity for aggressive behavior based on past evolutionary
demands, i.e., fighting for women and resources
 There are differences in obligatory parental obligation in raising children
 There is sexual dimorphism among males and females (12%)
 Violence occurs at the top and bottom of the hierarchy of males, too.
 Men die on average 7 years earlier than women
 Findings on aggression support the evolutionary, universal nature of
aggression and across many cultures
Jealousy
 May be related to the risk on not passing on genes
 Women appear to respond to imagining their partner emotionally involved
with another
 Men appear to respond to imagining their partner having sexual intercourse
 The “double shot” involves men believing that their woman will have
intercourse they will become emotionally involved while women have a
“reverse double shot” believing that if their mate becomes emotionally
involved they will have intercourse.
 Findings on jealousy support the universal nature of this issue and across
many cultures
Sexual variety
 With less investment in parenting the member will be less discriminating
and choose multiple mates, so, men will be far more likely to seek and be
interested in multiple women
 Huge study (n=16288) males desired 13 partners over 30 years and women
2.5 partners
 Appears to be a large and universal effect
Mate preference
 Women place more value on financial resources and the qualities that lead
to those resources (ambition, industriousness, and dependability) while
men place more value on physical appearance (a cue to fertility)
 Multi-culture research supports this contention
 Interesting studies on consent to sex with a stranger
o Supports the contention of increased sexual interest in men
o Stranger approached women and found the following results:
 55% would go on a date
 6% would go back to his apartment
 0% would have sex with him (issue of safety?)
o Stranger approached men and found the following result:
 50% would go on a date
 69% would go back to her apartment
 75% would have sex with her
Women often reacted with a feeling of insult while men often reacted with a feeling
of flattery.
Men had twice as many sexual fantasies as women with multiple partners in those
fantasies
When contacted by “a close personal friend” the results were very different:
o Acquaintance approached women and found the following result:
 91% would go on a date
 5% agreed to have sex with him
o Acquaintance approached men and found the following result:
 96% would go on a date
 50% agreed to have sex with her
Safety does not seem to be an issue as none of the respondents voiced concern over
their safety. Differences may be due to longstanding evolutionary differences
between men and women.
Same is true for extramarital affairs. Some 48% of American men and only 5% of
American women expressed a desire to engage in extramarital affairs.
Individual differences
 Adaptive self-assessment of heritable qualities
o A secondary reaction to heredity
o Skinny men vs. muscular men and their choice of aggressive
strategies based on things like individual’s size, strength and fighting
ability.
o The same is true for cooperativeness
 Frequency dependent alternative strategies
o The two sexes exist in roughly equal numbers because of frequency
dependent selection. If one sex becomes rare relative to the other,
evolution will produce an increase in the number of the rarer sex.
Frequency- dependent selection, cause the frequency of men and
women to remain roughly equal.
 Women’s mating strategies should center on two key qualities of potential
mates:
 Parental investment a man could provide
 The quality of his genes
o There is a trade off between selecting a man for his parenting abilities
and selecting a man for his genes.
 Restricted sexual strategies (a woman seeking a “highinvestment” mate makes a restricted sexual strategy which is
marked by a delay in intercourse and prolong courtship to make
sure there is commitment)
 Unrestricted sexual strategies (a woman is seeking “quality of
his genes,” there is no delay on her part in seeking intercourse
as this would defeat the main adaptive reason for her mating
strategy)
 These strategies are maintained by frequency dependent
selection
 The same may be true for psychopathy
 This is also a frequency-dependent selection strategy
 Psychopathy is marked by irresponsible and unreliable
behavior, egocentrism, impulsivity, inability to form long
term relationships, superficial charm, and a deficit in
social emotions like love, shame, guilt, empathy, and
remorse!
 More common among men than women
 Psychopathy is moderately heritable
 Psychopathy is often an exploitive sexual strategy
 Psychopathic men are often sexually precocious, have sex
with a large number of women, have more illegitimate
children, and are more likely to get divorced if they marry
than non-psychopathic men
 This short-term exploitive sexual strategy would increase
in populations marked by high geographic mobility in
which the costs to reputation associated with this strategy
are muted.
 This leads to the alarming idea that we may be witnessing
an increase in psychopathy in modern times as a result of
our mobility
 Cooperators and cheaters
 The increase in mobility may result in increases in the
psychopathic “strategy”
 Finally, environmental triggers result in specific sexual
strategies
o (father absent vs. father- present homes)
Limitations:
1) Because of the long history of human adaptation to the environment, it is
not possible to know, with certainty, what the precise selective forces on
humans have been.
2) Evolutionary scientists and evolutionary psychologists have just scratched
the surface of understanding the nature, details, and design features of
evolved psychological mechanisms.
3) Modern conditions are undoubtedly different from ancestral conditions in
many respects so that was adaptive in the past might not be adaptive in the
present.
4) Sometimes it is easy to come up with different and competing
evolutionary hypotheses for the same phenomenon. Competing theories
can be pitted against each other by allowing empirical research to evaluate
these theories.
5) At times, evolutionary theories have been accused of being untestable and
non-falsifiable. This is not true especially when one considers the research
on aggression, jealousy, and sexual selection strategies.