Transcript Evolutionary explanations of gender

Evolutionary explanation
of gender
Our biological sex
produces gendered behaviour
What is the driving
force behind it?
When discussing the
evolutionary explanation
make sure you first explain
the link with survival.
Selective pressures on males
and females
Gender differences have
evolved because they are
advantageous to both sexes
Mate choice: because reproduction
makes different demands on men and
women, they adopt different strategies
to choose mates.
Males produce lots of sperms and
can fertilise many females at little cost
Females produce few large eggs
once a month so they have only
300 opportunities to reproduce in
their lifetime
Males cannot be sure of paternity
Best strategy to enhance the chances
of reproducing their genes into
the next generation Careful mate
selection, monogamy, high parental
investment
Females select males displaying
genetic fitness. Like strength, status
and resources
Best strategy to enhance the chances
of reproducing their genes into
the next generation is to have sex with
as many fertile females as possible.
Physical aggressiveness to compete
with other men
Buss (1989)
Aim: to investigate if evolutionary explanations for
sex differences in human mate preferences are
found in all cultures. (if the same behaviours are
found across cultures it suggests that they could
have an evolutionary basis)
Sample: 37 samples from 33 countries, located on
six continents and five islands, number of
participants 10,047. mean age:23.05 years
Buss developed a questionnaire in which the
participants were asked to rate 18 characteristics
i.e. good financial prospects, good looks and
ambition and industriousness.
Results:
In most cultures:
“Good financial prospects”: was rated higher by
females than males
“Good looks” – All of the 37 samples showed
that males rated “good looks” in their mate more
than females did.
“ Ambition and industriousness”
In 34 of the 37 samples, females expressed a
higher valuation for “ambition and industriousness”
in a mate than did males.
Conclusions:
Buss concluded that sex differences
involving mate preferences for earning
potential, relative youth and physical
attractiveness were strongly confirmed
across cultures.
Buss’s findings support evolutionary
explanations of human behaviour;
specifically that mating behaviour should
differ according to gender, reflecting the
differences in reproductive capacities of
males and females.
However ...
The sample size in some countries were
small, only 28 men and 27 women
represented Iran.
Generalisations about mate preference can’t
be made from this small a sample.
A questionnaire may not be a valid measure of how we
select mates, for example older males do not always
seek younger females, so asking people about their
mate choice is different to measuring how they behave
in real life situations.
Schmitt (2003) did a large cross-cultural study and tested
16,288 participants from 53 countries. In each culture there
was a significant difference between women’s and men’s
preferences for variety in mates. In every case, males desired
a larger number of mates. This is consistent with evolutionary
theory, as males with low parental investment can afford to
have sex with a range of women whilst females are much choosier.
Furthermore ...
Thornhill & Palmer (2000) suggest rape has evolved as a
mechanism for sexually unsuccessful men to pass on their
genes, a number of other species use forced sex as a
reproductive strategy.
Ethics: the evolutionary theory justifies rape and other sexual
crimes and argues that they are inevitable.
The evolutionary explanation predicts that men would object
investing time and resources in a child who is not genetically
related, however this does not seem to be supported by reality
where men become step-fathers or adopt children.
Waynforth & Dunbar (1995)
Content analysis of personal ads
Findings:
Age
Males asked for Females 1-12yrs younger than them;
Females asked for Males 2-7yrs older
Attractiveness
Males mentioned own attractiveness 1.4 time less than Females but asked for
attractiveness twice as often
Resources
Males mentioned own wealth 1.7 time more than Females;
Females asked for wealth 4.5 times more than Males
The Hunter Hypothesis
The hunter-gatherer
hypothesis, Silverman and
Eals (1992), was proposed
as an evolutionary
explanation for sex
differences in spatial
ability. According to this
hypothesis, gender
differences in task
performance have arisen
from a process of natural
selection that favoured
hunting-related skills in
men and gathering–related
skills in women. One of
these skills is spatial
ability.
This hypothesis cannot
be tested directly, but
we can test its
predictions. Many
studies support this
hypothesis however
Hoffman (2011) found
that social factors
influence the
development of spatial
skills so it could be that
women are not given the
opportunity to develop
theses skills rather than
an evolutionary cause.
Human babies are not born ‘fully
formed’ because their brains are
comparatively underdeveloped. A
human foetus would have to
undergo a gestation period of 18
to 21 months instead of nine to be
born at a neurological and
cognitive development stage
comparable to that of a
chimpanzee newborn. However
the demands on the mother’s
metabolism would be too great
and the size of the pelvis is also a
limitation to the size of babies.
Furthermore, women need to
ensure the baby survives whilst
pregnant therefore invest in
their pregnancy and in feeding
the baby post birth
However in hunter-gatherer
societies child care is communal
with children being looked after
by many adults so there is less
pressure on the mother
Women did provide some food
e.g. growing vegetables and
grains. This avoided starvation of
the group when preys were
scarce.
They mainly carried out jobs
close to home
This is
speculative
(there is no
direct
evidence)
Kuhn & Stiner (2006)
Neanderthals - Did not divide
their labour and died out at
least 30 000 years ago.
Homo sapiens Divided their labour and
survived.
However there is not a single cause for the
Neanderthals’ extinction, change of climate
is also a possibility. It has also been argued
that they have been “absorbed” by the
interbreeding with modern humans.
Differences in Cognitive Style
(Baron-Cohen,2002)
Empathising –Systemising - E-S theory.
• Research has shown that women are better at
empathising (put themselves in shoes of others to
understand how they feel)whereas men are better are
systematising ((put things into sets).
• This gender difference may be the result of selection
pressure for males, who develop better hunting
strategies, and females, who focus on rearing
children.
• But this could be the consequence rather than the
cause of gender role (brain plasticity)or the effects of
socialisation of each gender.
Tend and Befriend- Taylor et al (2000)
Taylor studied animals (rats and monkeys) and humans. She
found gender differences in stressful situations:
• Women respond by- Tending (involves nurturing activities designed
to protect the self and offspring that promote safety and reduce
distress) and befriending (the creation and maintenance of social
networks that may aid in this process). This buffers the effects of
stress. Taylor who found females have raised levels of oxytocin
which reduces anxiety and increased sociability.
• Men do not show this increase in oxytocin and respond by
“fight or flight”
• This is supported by Ennis et al.(2001), sample: 67 college
students, ages 18–21 years (33 males and 34 females). Levels
of cortisol (stress hormone) were taken a week before an exam
(low stress) and immediately before an exam (high stress).
There was a significant increase in cortisol levels in males
participants, but not in females. This shows that men respond
to stressful situations by preparing to ‘fight or flight’, while
women respond with developing a support network which
buffers the effects of stress.
Evaluation of the evolutionary explanation
of gender
Deterministic
Hypotheses are difficult or impossible
to test adequately.
Relies on post hoc interpretations of
controversial evidence (i.e. skeletons
of Neanderthals at least 30 000 years
old)
Evolutionary psychologists tend to
assume that their own current cultural
context represents a universal human
nature. (Have gender roles changed
over time? Are they the same in different
cultures?)
According to Taylor: our biological
heritage is not destiny but rather a
force that "influences and interacts
with social, cultural, cognitive and
emotional factors."
It assumes that physical and
psychological traits are
predetermined and programmed
while virtually ignoring nongenetic factors involved in
human development. Even when
evolutionary psychologists
acknowledge the influence of the
environment, they reduce its role
to that of a trigger of the
predetermined developmental
instructions supposed to be
encoded in a person's genes.
Reductionist: does not take into
account moral values and free
will.