,Evolutionary Explanations For Partner Inter-sexual selection
• Inter-sexual selection is bet ween (inter) the sexes - the strategies that males use to
Preferences select females or females use to select males. Inter-sexual selection is the preferred
strategy of the female, quality over quantity (ova are rarer than sperm).
Key points: • Robert Trivers (1972) pointed out that the female makes a greater investment of time,
• Sexual selection: An evolutionary explanation for partner commitment and other resources before, during and after the birth of her offspring.
preference. Attributes or behaviours that increase reproductive Both sexes are choosy, because both stand to lose if they invest resources in
success are passed on and may become exaggerated over substandard partners. But the consequences of making a wrong partner choice are more
succeeding generations of offspring serious for the female, so it pays for her to be especially selective. Therefore, the
• Human reproductive behaviour: This refers to any behaviours female's optimum mating strategy is to select a genetically fit partner who is able to
which relate to opportunities to reproduce and thereby increase provide resources. It is this female preference which determines which features are
the survival chances of our genes. It includes the evolutionary passed on to the offspring.
mechanisms underlying our partner preferences, such as mate • For example, if height is considered an attractive male trait by females then it would
choice and mate competition. increase in the male population over successive generations. This is because, in each
generation, females will select the tallest males and thus that characteristic gradually
Sexual selection becomes exaggerated (a runaway process).
• Dar win's (1871) concept of sexual selection concerns the • Ronald Fisher (1930) developed a sexy son’s hypothesis - the genes we see today are
selection of those characteristics that aid successful those that enhanced reproductive success. A female who mates with a male who has a
reproduction (rather than survival). Some physical certain characteristic then will have sons who inherit this 's exy' trait. Then her sons
characteristics, such as a male peacock's tail, are a sign of are also more likely to be selected by successive generations of females who will mate
genetic fitness. with her offspring. Therefore the preference for this 's exy' trait is perpetuated.
• Females who select males with such characteristics are more
likely to produce robust offspring and therefore the preference Intra-sexual selection
for such a tail is perpetuated in future generations. Other • Intra-sexual selection is within (intra) each sex - such as the strategies bet ween males
characteristics, such as aggressiveness, are adaptive because to be the one that is selected. It is the preferred strategy of the male, quantity over
they provide an advantage for a male over competitors for quality (there is a plentiful supply of sperm).
reproductive rights. • There is competition bet ween males to be selected to mate with a female. The winner of
• The aggressive characteristics that allowed the animal to the competition reproduces and therefore the characteristics that contributed to his
reproduce in the first place are passed on to offspring if they are victory may be passed on to his offspring (and losers do not pass on their losing'
genetically determined and the genes that gave rise to the characteristics because they don't mate).
characteristics remain in the population. • This strategy has given rise to dimorphism (means 't wo forms') - males and females end
up looking very different because of intra-sexual selection. For example, in any physical
Anisogamy competition bet ween males, size matters. Larger males have an advantage and are
• The basis of human reproductive behaviour is anisogamy, which therefore more likely to be reproductively successful. On the other hand, females do not
refers to the differences bet ween male and female sex cells compete for reproductive rights so there is no evolutionary drive towards favouring
(gametes). Male gametes (sperm) are small, highly mobile, larger females. However, in females youthfulness is selected because males have a
created continuously in vast numbers from puberty to old age preference to mate with younger more fertile women (as indicated in humans by, for
and do not need much energy to be produced. example, a large waist-to-hip ratio).
• In contrast, female gametes (eggs or ova) are relatively large, • Intra-sexual selection also has behavioural consequences, although these are
static, produced at intervals for a limited number of fertile controversial. The characteristics that are favoured and passed on are those that allow
years and require a significant investment of energy. female is a male to outcompete his rivals, including deceitfulness, intelligence and aggression. For
much rarer resource: Anisogamy is important in partner example, males may benefit from behaving aggressively in order to acquire fertile
preference because it gives rise to t wo types of sexual selection. females and protect them from competing males. This leads to the selection of
aggressiveness in males.
, Evaluation (research support for inter-sexual selection)
P: One strength is evidence supporting the specific role of female choosiness in
heterosexual partner preference
E: Clark and Hatfield sent male and female psychology students out across a university
campus. Their approached other students individually and asked ‘I have been noticing Evaluation (Social and cultural influences
you around campus. I find you to be very attractive, would you go to ben with me underestimated)
tonight?’ And no single female student agreed to the request however 75% of males did P: One limitation is that evolutionary theories
immediately. overlook the influences of social and cultural factors
E: This supports the view that females are choosier than males when is come to on partner preference.
selecting sexual partners and that males have evolved a different strategy to ensure E: Partner preferences over the past century have
reproductive success undoubtedly been influenced by rapidly changing social
CA: However some psychologist may argue that both males and females adopt similar norms of behaviour. These develop much faster than
mating strategies when seeking long-term relationships and both are choosy and look evolutionary timescales imply and have instead come
for partners who are loving, loyal and kind. about due to cultural factors (e.g. availability of
C: Despite this its still a weakness because the findings of the study suggest that contraception). Women's greater role in the workplace
females are more picky when choosing a partner means they are no longer dependent on men to provide
for them (despite the ongoing inequality in earning
Evaluation (Research support for intra-sexual selection) power). Tamas Bereczkei et al. (1997) argue that this
P: Another strength is evidence to support the predictions of sexual selection theory. social change has consequences for women's mate
E: David Buss (1989) carried out a survey of over 10,000 adults in 33 countries. He preferences, which may no longer be resource-
asked questions relating to a variety of attributes that evolutionary theory predicts oriented.
are important in partner preference. He found that females placed greater value on E: Therefore, partner preferences today are likely to
resource-related characteristics than males did, such as good financial prospects and be the outcome of a combination of evolutionary and
ambition. Males valued physical attractiveness and youth (as signs of good cultural influences. Any theory that fails to account
reproductive capacity) more than females did. for both is a limited explanation.
E: These findings reflect consistent sex differences in partner preferences and support CA: However some psychologist may argue
the predictions from sexual selection theory. evolutionary explanations are still valuable because
CA: However some psychologist may argue that Buss’s findings do not necessarily cross-cultural patterns in mate preferences remain
demonstrate evolved, biological preferences. Instead, they may reflect cultural and remarkably consistent despite social change
social influences. C: Despite this, it’s still a limitation because by
C: Despite this, its still a strength because the findings clearly demonstrate the overlooking the influence of social and cultural we a
differences bet ween males and females when selecting a partner which increases limiting knowledge of sexual selection.
usefulness
• Inter-sexual selection is bet ween (inter) the sexes - the strategies that males use to
Preferences select females or females use to select males. Inter-sexual selection is the preferred
strategy of the female, quality over quantity (ova are rarer than sperm).
Key points: • Robert Trivers (1972) pointed out that the female makes a greater investment of time,
• Sexual selection: An evolutionary explanation for partner commitment and other resources before, during and after the birth of her offspring.
preference. Attributes or behaviours that increase reproductive Both sexes are choosy, because both stand to lose if they invest resources in
success are passed on and may become exaggerated over substandard partners. But the consequences of making a wrong partner choice are more
succeeding generations of offspring serious for the female, so it pays for her to be especially selective. Therefore, the
• Human reproductive behaviour: This refers to any behaviours female's optimum mating strategy is to select a genetically fit partner who is able to
which relate to opportunities to reproduce and thereby increase provide resources. It is this female preference which determines which features are
the survival chances of our genes. It includes the evolutionary passed on to the offspring.
mechanisms underlying our partner preferences, such as mate • For example, if height is considered an attractive male trait by females then it would
choice and mate competition. increase in the male population over successive generations. This is because, in each
generation, females will select the tallest males and thus that characteristic gradually
Sexual selection becomes exaggerated (a runaway process).
• Dar win's (1871) concept of sexual selection concerns the • Ronald Fisher (1930) developed a sexy son’s hypothesis - the genes we see today are
selection of those characteristics that aid successful those that enhanced reproductive success. A female who mates with a male who has a
reproduction (rather than survival). Some physical certain characteristic then will have sons who inherit this 's exy' trait. Then her sons
characteristics, such as a male peacock's tail, are a sign of are also more likely to be selected by successive generations of females who will mate
genetic fitness. with her offspring. Therefore the preference for this 's exy' trait is perpetuated.
• Females who select males with such characteristics are more
likely to produce robust offspring and therefore the preference Intra-sexual selection
for such a tail is perpetuated in future generations. Other • Intra-sexual selection is within (intra) each sex - such as the strategies bet ween males
characteristics, such as aggressiveness, are adaptive because to be the one that is selected. It is the preferred strategy of the male, quantity over
they provide an advantage for a male over competitors for quality (there is a plentiful supply of sperm).
reproductive rights. • There is competition bet ween males to be selected to mate with a female. The winner of
• The aggressive characteristics that allowed the animal to the competition reproduces and therefore the characteristics that contributed to his
reproduce in the first place are passed on to offspring if they are victory may be passed on to his offspring (and losers do not pass on their losing'
genetically determined and the genes that gave rise to the characteristics because they don't mate).
characteristics remain in the population. • This strategy has given rise to dimorphism (means 't wo forms') - males and females end
up looking very different because of intra-sexual selection. For example, in any physical
Anisogamy competition bet ween males, size matters. Larger males have an advantage and are
• The basis of human reproductive behaviour is anisogamy, which therefore more likely to be reproductively successful. On the other hand, females do not
refers to the differences bet ween male and female sex cells compete for reproductive rights so there is no evolutionary drive towards favouring
(gametes). Male gametes (sperm) are small, highly mobile, larger females. However, in females youthfulness is selected because males have a
created continuously in vast numbers from puberty to old age preference to mate with younger more fertile women (as indicated in humans by, for
and do not need much energy to be produced. example, a large waist-to-hip ratio).
• In contrast, female gametes (eggs or ova) are relatively large, • Intra-sexual selection also has behavioural consequences, although these are
static, produced at intervals for a limited number of fertile controversial. The characteristics that are favoured and passed on are those that allow
years and require a significant investment of energy. female is a male to outcompete his rivals, including deceitfulness, intelligence and aggression. For
much rarer resource: Anisogamy is important in partner example, males may benefit from behaving aggressively in order to acquire fertile
preference because it gives rise to t wo types of sexual selection. females and protect them from competing males. This leads to the selection of
aggressiveness in males.
, Evaluation (research support for inter-sexual selection)
P: One strength is evidence supporting the specific role of female choosiness in
heterosexual partner preference
E: Clark and Hatfield sent male and female psychology students out across a university
campus. Their approached other students individually and asked ‘I have been noticing Evaluation (Social and cultural influences
you around campus. I find you to be very attractive, would you go to ben with me underestimated)
tonight?’ And no single female student agreed to the request however 75% of males did P: One limitation is that evolutionary theories
immediately. overlook the influences of social and cultural factors
E: This supports the view that females are choosier than males when is come to on partner preference.
selecting sexual partners and that males have evolved a different strategy to ensure E: Partner preferences over the past century have
reproductive success undoubtedly been influenced by rapidly changing social
CA: However some psychologist may argue that both males and females adopt similar norms of behaviour. These develop much faster than
mating strategies when seeking long-term relationships and both are choosy and look evolutionary timescales imply and have instead come
for partners who are loving, loyal and kind. about due to cultural factors (e.g. availability of
C: Despite this its still a weakness because the findings of the study suggest that contraception). Women's greater role in the workplace
females are more picky when choosing a partner means they are no longer dependent on men to provide
for them (despite the ongoing inequality in earning
Evaluation (Research support for intra-sexual selection) power). Tamas Bereczkei et al. (1997) argue that this
P: Another strength is evidence to support the predictions of sexual selection theory. social change has consequences for women's mate
E: David Buss (1989) carried out a survey of over 10,000 adults in 33 countries. He preferences, which may no longer be resource-
asked questions relating to a variety of attributes that evolutionary theory predicts oriented.
are important in partner preference. He found that females placed greater value on E: Therefore, partner preferences today are likely to
resource-related characteristics than males did, such as good financial prospects and be the outcome of a combination of evolutionary and
ambition. Males valued physical attractiveness and youth (as signs of good cultural influences. Any theory that fails to account
reproductive capacity) more than females did. for both is a limited explanation.
E: These findings reflect consistent sex differences in partner preferences and support CA: However some psychologist may argue
the predictions from sexual selection theory. evolutionary explanations are still valuable because
CA: However some psychologist may argue that Buss’s findings do not necessarily cross-cultural patterns in mate preferences remain
demonstrate evolved, biological preferences. Instead, they may reflect cultural and remarkably consistent despite social change
social influences. C: Despite this, it’s still a limitation because by
C: Despite this, its still a strength because the findings clearly demonstrate the overlooking the influence of social and cultural we a
differences bet ween males and females when selecting a partner which increases limiting knowledge of sexual selection.
usefulness
