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sexual selection & human reproductive behaviour

Darwin proposed that species do not just evolve through Natural selection but also “Sexual Selection”– A view that competition for mates between individuals of the same sex affects the evolution of certain traits. He decribed two processes through which sexual selection took place: intrasexual selection and intersexual selection. 

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 then able to pass on their genes whilst the losers aren’t. The genes of the successful male are then passed on to their offspring.

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 and support to the offspring (e.g. economic resources). 

Men have a greater desire for casual sex and tend to seek sex earlier in a relationship. This is because men can produce several children within a year whilst women cannot. Men have an evolutionary desire to impregnate a woman as soon as they can before moving on. This is 

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sexual selection & human reproductive behaviour

supported by Clark and Hatfield’s study which found that when 

approached by total (female) stranger, 75% of men agreed to have sex with the female stranger whilst no women agreed to have sex with the male stranger. However, this validity of this study can be questioned as the study was carried out on a university campus using students therefore the results may not be generalised to a wider population demonstrating sample bias. There are also ethical issues as the study could have caused some psychological harm as it involved deception. 

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-bearing support. Women are particularly choosey as they have to make an obligatory biological investment in the child. Females therefore look for good resources, physical strength etc. This theory is also applicable in real life as women need to know that the father of their child will be able to provide for them. Buss used 10,000 plus participants from 37 cultures and explored what males and females look in a marriage partner. Women wanted a partner with good financial prospects whilst men wanted physical attractiveness. Men also wanted younger women which indicates fertility thus providing valid support for the relationship between sexual selection and human reproductive behaviour. 

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sexual selection & human reproductive behaviour

However, Bereczkel et al (1997) found that women now advertise for males that are more family orientated therefore are less concerned about resources thus contradicting this theory of choosiness and human reproductive behaviour. 

Also Buss’s study may not provide strong support for the relationship between sexual selection and human reproductive behaviour as although they provide information about expressed mate choices, this may be different for information about actual mate choice (in which compromises are made). However, another study conducted by Buss of actual married couples from 29 cultures supported the original results that men do actually marry women that are younger than them, thus increasing the validity of this explanation. 

In contrast, some critics argue that men may in fact prefer younger women due to social power. Younger women are easier to control and therefore preferable as mates. Kenrick et al. rejected this theory by finding that teenage males are most attracted to women 5 years older than them; these women are certainly not easily controlled.

 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 

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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.

Evolutionary explanations of sexual selection have faced criticisms about being choosey and the costs that can be incurred. In real life this would require time and energy and would result in the creation of fewer children than if we were to mate with any available partner. However, they don’t outweigh the advantages of being choosy as it enables the production of high quality offspring whose genes are more likely to be passed on. 

In addition, there is the issue of gender bias in studies of short term mating. Although research consistently reports that men more than women have a desire for a variety of sexual partners and a greater willingness for causal sex, men could never have evolved this desire in the absence of willing females. Despite the fact that short term mating carries a considerable potential cost to the woman there must also be some benefits. Greiling and Buss suggest that women could profit in a number of ways for example, using short term mating as a way of leaving a poor quality wedding. As a result, explanations that emphasise the advantages of short term mating only to males, offer a gender biased view of mating behaviour.


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sexual selection & human reproductive behaviour

All in all, the evolutionary approach to sexual selection can be criticised as being reductionist. It reduces complex ideas into simplistic terms as other factors other than trying to create good offspring influences mate choice. Emotion is a big factor on helping to choose a mate. This theory is also determinist as it ignores our free will which we use on a daily basis to select whether we want to choose a person who is attractive or not. Some people stay with their partners who are infertile therefore this theory cannot be applied situations such as this. Cultural differences also influence our mate choices as in some collectivist cultures women don’t get the chance to choose their mate, instead the family does (arranged marriages).

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