From the Mark Scheme
For AO1 credit candidates may outline the background to research on sexual selection and human
reproductive behaviour in terms of evolutionary theory, selfish gene etc. Also relevant would be a
description of the detailed processes involved in sexual selection, including intra-sexual (mate competition)
and inter-sexual (mate choice) selection. Other factors affecting mate choice, such as parental investment
theory, and variations such as short and long term mate preferences, would also be creditable AO1
material.
Research with non-human animals may earn AO1 and AO2/AO3 marks insofar as it is made explicitly
relevant to human reproductive behaviour.
Research studies may be presented as either AO1 (illustrating the relationship between sexual selection and human
reproductive behaviour) or as AO2/AO3.
There are a variety of routes to AO2/AO3 credit. Research findings, such as Buss’s cross-cultural studies
and dating research, would be an effective source of AO2/AO3 marks. Evaluation of research eg use of
questionnaires and social desirability issues, may earn marks if the implications for the reliability and
validity of findings are clear.
Comparison with alternative approaches eg social psychological explanations, may earn marks if they are
used as effective AO2/AO3.
Candidates may also take a more theoretical approach focusing for instance on issues, debates and
approaches relevant to this area.
Issues, debates and approaches in this area include free will and determinism. If sexual selection, human
reproductive behaviour and the relationships it involves are driven by purely evolutionary considerations,
then they would be highly predictable. In fact human reproductive behaviour has changed dramatically over
the last century, with non-heterosexual relationships, widespread use of contraception, and couples
choosing not to have children. This implies that we have more control (free will) over our behaviour than is
implied by the evolutionary approach. Candidates may also refer to reductionism, cultural differences,
gender biases and socially sensitive research.
Answer Take 1
Sexual Selection theory by Darwin proposes that species do not just evolve through Natural
selection but also “Sexual Selection”– This is the view that competition for mates between
individuals of the same sex affects the evolution of certain traits. Any physical trait that enhances
reproductive success will gradually be passed down and enhanced over time.
Darwin proposed that animals possess features that make them attractive to members of the
opposite sex and allow them to compete better with members of the same sex. An example of
this in humans is the relative hairlessness of human beings compared with other great apes; such
a feature allowed our ancestors to not only keep cool but to advertise to others good hygiene
(Pagel et al). This trait therefore becomes desirable in a mate and is the result of sexual
selection. The greater loss of body hair in women would have been through greater pressures on
women from sexual selection in comparison to men. The strange case of the peacocks tail seems
to go against this however as it offers no advantage; it is heavier, more noticeable by predators
and does not help the peacock fly any better.
Different sexual selection pressure occurs between the genders due to differences in gametes
(Eggs & Sperms). Males have millions of sperms however can never be certain of paternity and
suffer little cost to reproduction therefore natural selection favours them maximizing their mating
opportunities. Females however have a limited number of eggs with each representing a huge
investment during and after pregnancy but are certain of paternity. Due to this they must be more
choosy in finding strong, healthy and committed males with resources.
There are then two types of sexual selection that take place in relation to human reproductive
behaviour: Intra-sexual selection in males and Intersexual selection in females.
Intra-sexual selection occurs in males who compete with each other for access to females. As a
consequence of this men for example have evolved indicators such as strong jaw lines, high
cheekbones triangular backs and wide shoulders as these are signs of strength and testosterone
which women will seek. High levels of testosterone can damage immune systems how- ever and
they would only be able to be displayed in strong males (Handicap principle). Thornhill et al also
found that women tended to prefer men with such traits suggesting these are indicators within
sexual selection theory for humans. Men on the other hand look for signs of fertility through youth
and physical attraction as this maximizes reproductive success for them.
Intersexual selection occurs between women who then go on to select men who show the best
indicators of providing good genes for offspring, the ability to protect her and her child, provide
status and resources. Psychologists propose it is this evolutionary behaviour that then shapes
mate selection in males and females. Males should in theory look for females showing signs of
fertility, youth and physical attraction and females should seek males showing signs of genetic
strength, masculine features and the ability to provide and protect.
Can you work out what’s missing from this essay?
Take 2
Darwin suggests that sexual selection is more important than natural selection in shaping human
reproductive behaviour. An example of sexual selection operating over time is the relative
hairlessness of human beings compared to other apes. Pagel and Bodmer (2003) claim that this
is because hairlessness allowed humans to ‘advertise’ their reduced susceptibility to infection,
this trait therefore became desirable in a mate (a consequence of sexual selection).
There are two types of sexual selection: intrasexual and intersexual. Where conditions favour
polygyny, males must compete with other males for access to a female mate. This is intrasexual
selection (selection within the same sex). In contrast, females who invest heavily in their
offspring need to make the right choice in a mate and can afford to be choosy and engage in
intersexual selection (selection between the sexes). Thus, males compete and females choose.
Intersexual selection involves preference for a member of the opposite sex who possesses
certain qualities; to compensate for this, humans have developed certain characteristics to
improve their chances of reproduction and ultimately, survival. For example, human facial
attractiveness is linked to the advertisement of ‘good genes’. Thus, individuals possessing
attractive facial features are preferred as mates because of the benefit of passing on these
attractive genes.
Buss (1989) investigated the sex differences in human mate preferences across 37 cultures. By
using questionnaires to measure the importance of factors affecting mate choice, he found that
women from all cultures showed a preference for men with resources. Men universally
preferred physically attractive and younger women, and some characteristics (intelligence and
kindness) were desired universally by both sexes.
However, a major flaw of Buss’s (1989) investigation is in the methodology. Buss used
questionnaires to assess the importance of factors affecting mate choice. It is likely that people
gave social desirable answers to prevent themselves from being judged, compromising the
validity of the study. Furthermore, although a large sample size was used, it is not a
representative sample as people living in rural areas and less educated individuals were
underrepresented. The sampling method also differed across cultures, affecting the reliability of
the findings as variables were not controlled.
Another weakness of the research documenting sex differences in mate choice is that focus is
usually drawn to preference, as opposed to real-life choices. While people may express a
preference, they often have to settle for less.
On the other hand, a strength is that there is evidence for evolutionary influences on facial
preferences. Interest in attractive female faces emerges early in the first year of infancy, this
implies that the preference for attractive faces is likely to be an evolved response (Langlois et
al. 1987).
Furthermore, research support for facial preferences comes from Penton-Voak et al. (1999).
They found that women’s preferences for attractive faces are not static. Women are attracted to
masculine-looking men during their fertile time and show a preference for feminine-looking
men during less fertile times. This may indicate that less-masculine looking men may make
better long term partners, but masculine-looking men produce the strongest, healthiest children.
In evaluating Darwin’s explanation of the relationship between sexual selection and human
reproductive behaviour, it is important to point out that it does not account for homosexual
relationships which do not contribute to reproductive success and the passing of genes. Due to
this heterosexual bias, we cannot generalise this explanation to all relationships.
Another weakness is the overemphasis placed on evolutionary factors. Nicolson (1999) suggests
that choosing a mate is likely to be based on a whole range of issues, not simply evolutionary
influences. We can therefore argue that Darwin’s explanation is too simplistic and reductionist
as it fails to account for other possible influences such as social norms.
It can also be argued that evolutionary explanations are determinist. This view suggests that we
are victims of evolution and driven by the need to reproduce and pass on good genes to our
offspring. According to this view, we would mate with someone who is physically attractive.
However, this ignores the role of free will. Rather there are other possible factors for choosing a
mate, such as personality.
Sex differences in reproductive behaviour can also be explained by an alternative perspective.
For example, the behavioural model would suggest that social learning theory has a major role
in shaping human reproductive behaviour. The media, for instance, often portrays males as
sexually promiscuous, thus it is likely this behaviour is imitated.
Take 3
Intrasexual selection is the evolutionary process by which members of one sex (usually males) compete with each
other for members of the opposite sex. The victors are able to pass on their genes while the losers are not. The
factor that made the male successful is then passed on to the offspring, helping to ensure their survival and the
passing on of their genes.
Intersexual selection refers to the fact that members of each sex have innate preferences for mates with certain
characteristics. The preferences of one sex determine the areas in which the other sex must compete (e.g. physical
attractiveness for women). These indicators reveal traits which could be passed on to offspring (e.g. height) or which
could give protection & support to the offspring (e.g. economic resources).
Men have a greater desire for casual sex & tend to seek sex earlier in the relationship. This is because men can
produce several children within a year, while women cannot: men have an evolutionary desire to impregnate a
woman as soon as they can before moving on. Men experience a decrease in sexual attraction following sex to
prevent them from spending too much time with any one woman.
For long-term mating, both sexes must invest heavily in any offspring. Choosiness is therefore high in both sexes, as
they wouldn't want to waste valuable resources if their mate is providing poor genes or little child-rearing support.
Women are particularly choosy, as have to make an obligatory biological investment in the child. Females thus look
for good resources, physical strength, etc.
Buss explored what males & females look in a marriage partner for 10,000+ folks from 37 cultures. The results
supported predictions of evolutionary explanations of sexual selection. For example, women want good financial
prospects: men with financial resources to provide for children. Men want physical attractiveness, which research
has consistently confirmed to be linked av fertility & health. Men also wanted younger women: an indication of
fertility.
Studies such as Buss' may suffer from a validity problem, as although they provide information about expressed
mate choices, this may be different to info about actual mate choice (in which compromises are made). However,
another study by Buss of actual married couples from 29 cultures supported the original results. For example, men
do marry younger women.
Although Buss' study supports the idea that men prefer younger women, this may not be because of fertility. Some
critics have tried to explain this in terms of social power: younger women are easier to control and are therefore
preferable as mates. Kenrick et al. rejected this hypothesis by finding that teenage males are most attracted to
women 5 years older than them: these women are not easily controlled.
Evolutionary explanations of sexual selection have faced some scepticism as being choosy about sexual partners can
be costly, as it requires time and energy, and would result in the creation of less children than if we were to mate
with any available partner. These disadvantages of being choosy are real, but they do not outweigh the advantages
of being choosy: choosiness allows the production of high-quality offspring whose genes are much more likely to be
passed on.
The claim that males are more likely than females to seek short-term mating opportunities is supported by research.
Clarke & Hatfield found that 75% of males were willing to have sex with an attractive stranger, but no females were.
This suggests that males have evolved such mechanisms to increase reproductive success.
Research suggests that female mate choice varies across the menstrual cycle. Penton-Voak et al. found that females
preferred more masculine faces during more fertile phases & more feminine faces during less fertile phases. This
suggests that females may choose a partner whose feminine features suggest kindness & cooperation in childrearing, but mate with a male who possesses desirable qualities in offspring.
Visual & chemical indicators can tell men when women are at their most fertile stage in the menstrual cycle.
According to evolutionary explanations, men would find women most attractive at these times. Miller et al.
analysed tips earned by lap dancers. They earned almost twice as much money in these phases, showing that men
are most attracted to women when in the most fertile phase of the menstrual cycle.
There may be a gender bias in research on short-term mating. Although short-term mating can be costly to females,
they could also profit from it. They may use short-term mating as a way of ending a relationship with a poor-quality
male or as a way of producing more genetically diverse offspring.
Take 4
Human reproductive behaviour is an evolutionary approach; it tries to explain human behaviour from the
point of view of how it might have evolved. It is based on the idea that our behaviour is influenced by instincts
left over from our evolutionary past when they were adaptive, so increasing our chances of survival. Sexual
selection is the process in which a species changes over time as a result of the passing on of the genes that
make one individual more attractive than another. This happens because members of the same species
compete with other members of the same sex for a mate. The members who have features that make them
more attractive are more likely to reproduce and pass on their genes. This theory is important in explaining
why males and females of some species look so different, for example, male and female peacocks because
the males have long brightly coloured tails which reduce chances of survival with predators however as
female peacocks are attracted to this feature, it shows that males with better tails have more chance of
reproducing and passing on their genes therefore the characteristic evolves in the species even though it
reduced survival.
There are two types of sexual selection, intrasexual selection (mate competition) and intersexual (mate
choice). Intrasexual selection is when member of one sex (usually males) compete with each other for access
to members of the opposite sex. The victors are able to make and pass on their genes, whereas the losers
do not. Whatever trait leads to success in these same sex contests will be passed on to the next generation.
Intersexual is a form of selection which involves the preferences of one sex for members of the opposite sex
who possess certain qualities, for example, if females prefer tall men, over time there would be an increase
in the number of tall males in the population. The preference of one sex determines the areas in which the
other sex must compete. This may be in terms of plumage (in peacock) or economic resources (in humans).
Ridley pointed out that in the past 100,000 years the human species has hardly evolved at all and therefore
our psychology is very much as it would have been when we were all hunter gatherers. He believed that men
are driven to behave in ways that will maximize the probability that they will reproduce. (Gain resources, gain
power, lure women, mate with as many women as possible etc.) Where as women are driven by the desire
to secure the best genes possible for their children and to be protected by a powerful man in order to
maximize the chances of their children surviving. Thornhill and Palmer went further and proposed that rape
has evolved as a mechanism to allow unsuccessful men to reproduce. This theory has proved highly
controversial. Rose and Rose believe that this amounts to justifying rape ad a good this for a species.
Buss aimed to test the hypothesis that the factors affecting mate choice in men and women are consistent
across a range of cultures and therefore demonstrating the role of evolutionary factors. Buss used
questionnaires to measure the importance of factors affecting mate choice. He found that 36/37 cultures
women emphasized good financial prospects in a mate than did men and in 29/37 cultures women placed
significantly more emphasis on ambition and industriousness than did men. This is in line with evolutionary
theory as they are trying to secure a mate with good resources to care for them and their children. In all 37
cultures men rated ideal age of a mate as younger than did women and looks were more important in men
than women in all 37 cultures. This is because youth and attractiveness signifies fertility. Therefore most
findings supported the idea that men and women differ consistently in the characteristics they find attractive
in a potential mate. This shows evidence of intersexual selection as males and females look for different
things in a potential mate.
However there are many strengths and weaknesses. For example in the case of homosexuality, Buss’s
argument cannot account for homosexual relationships which clearly do not contribute to the survival of the
species. Same sex relationships seem to have existed in most cultures throughout recorded history, so
explanation for sexual selection cannot explain these relationships, therefore it cannot be generalised to all
relationships.
A second weakness related to mate choice in real life. Buss’s survey of mate choice suffers from a serious
problem of validity. The research has focused on preferences rather than on real life choices. For example,
people may express a preference for an ideal partner (intelligent, kind etc.) but may have to settle for less.
This therefore means that the study does not tell us about actual mate choice. However a study of real life
marriages has conformed many of these predictions, such as, men do choose younger women (Buss).
One major flaw of this study is in the methodology. Although a large sample size was used, Buss did not use
a representative sample. In his study people living in rural areas were underrepresented as were those
individuals who were less educated as the study relied on people completing a questionnaire. The sampling
method created another problem as is varied widely across cultures and he used opportunity and selfselecting samples, both of which are not random and could introduce sampling bias.
However there is research evidence to support Buss’s ideas. Schmitt tested the idea of sex differences in
mating preferences and surveyed over 16000 people from 53 countries. Schmitt found that men reported
wanting to have sex with more people than women did, supporting the idea of sex differences in human
reproductive behaviour.
Another sex difference is facial preferences. Facial preferences can also play an important role when
choosing a mate. The evolutionary view is that human facial attractiveness is liked to good genes. Research
has shown that females are attracted to male’s faces that have “masculine” features such as large jaw and
prominent cheek bones. These characteristics are seen as a result of the testosterone, but the hormone may
also become a handicap because it is also know to supplement the immune system. This means that only
“healthy” individuals can afford to produce these masculine traits indicating their dominance and strength of
their immune system to women who are then more likely to select them as possible mates. (Thornhill and
Gangestad). Males also have clear facial preferences, preferring females with more child like faces,
including large eyes, small noses and full lips. These characteristics indicate youth and fertility, making them
more attractive as potential mates (Thornhill and Gangestad). Interest in attractive female faces emerges
early in the first year of infancy this implies that the preference is more likely to be an evolved response rather
than a learned behaviour. There is also a significant degree of cross cultural agreement in rating of
attractiveness (Perrett). This shows that the criteria for facial attraction is not determined by cultural
conventions.
Intersexual selection has been discussed in Buss’s research but there are also consequences for intrasexual
selection. Sperm competition is a type of intrasexual competition and it is important in determining which
male is successful in fertilising her egg. This perspective suggests competition for fertilisation not females.
This has resulted in males evolving larger penises, larger testicles, larger ejaculates and faster swimming
sperm. Harvey and May suggested that ethnic difference in testicle size may reflect adaptive differences in
mating strategies within different populations. Measurements made during autopsy showed that testicle size
in two Chinese samples was approx half the size of testicles in a Danish sample. This could be due to the
norm of arranged marriages in Chinese culture and therefore a reduction in sperm competition as they will
have a sexual relationship with one partner.
One evaluation point is the fact that some psychologists argue that evolutionary psychology is not the answer
to everything, Nicolson argues that the relevance of evolutionary factors has been overemphasised; she
argues that this is not how people really live and choose partners and decisions are more likely to be made
on a whole range of issues. She suggested that evolutionary influences on human reproductive behaviour
are lost in today’s social context. This therefore suggests that evolutionary explanations are reductionist as
they are too simplistic and focus on innate instincts and ignore another other important contributory factory.
This approach ignores the role of social or cognitive factors.
It could also be argued that evolutionary explanations are deterministic. It assumes that all men will be
motivated to have a high number of sexual partners and be less inclined towards a long term committed
relationship and that all women are motivated by the resources a male has to offer. This ignores the role of
free will and choice that both males and females have in deciding what relationships they want. There are
cases of males that settle down with one person at an early age and women who do not decide to settle
down and have children.
Sex differences in reproductive behavior could also be explained by an alternative perspective. It could be
argued using the social approach that the idea that men are motivated to sleep around is something that is
created and reinforced by society and socialization. Behavioural approaches would also explain this via the
role of the media. The media could have a role via social learning theory as there are many social models in
the media where males are exposed to this behaviour. Sexually promiscuous behavior is also celebrated by
the male peer group and this could be an alternative reason for this sex difference.
There are loads more on the inter net – which one do you like best? Can you see common themes and styles in
these essays?