Evolutionary theories

• Sexual Selection and Human Reproductive behaviour

  The evolutionary approach sees male and females as being subjected to different selective pressures, which therefore leads them to use different strategies to maximise their reproductive success.

  These strategies tend to be dictated by Anisogamy and Parental Investment
• Anisogamy

  Anisogamy = differences between male and female sex cells.

  Males’ sex cells (sperm) are produced in large quantities, quickly replenished and created continuously from puberty to old age. On the contrary, females’ sex cells (eggs or ova) take a lot of energy to produce, are created in limited numbers during specific time intervals and their production only lasts for a certain number of fertile years. A consequence of this is that there is no shortage of fertile males to mate with, but a fertile woman is a rare ‘resource’.
• Parental investment: There are biological differences between men and women in terms of parental investment. For women, after conception they then carry the child in the womb for nine months, give birth and then breastfeed. In comparison to this, men carry a relative lack of responsibility. Therefore, there are greater consequences for a woman who makes a bad choice in a partner. If they do not choose a partner who is committed to the relationship, capable of protecting them and their child, their child may not survive and genes may not be passed on.
• A successful mating strategy would be to sleep with as many women as possible in the hope that at least in some cases their genes were passed on – this strategy is enabled by the relative lack of parental investment and anisogamy. Males cannot afford to be choosy in their choice of partner, because anisogamy dictates that females are a ‘rare resource’. Because there are many fertile males for the female to choose from, this instead leaves men competing with other men to be selected. This strategy of competing within a group of males to be chosen is referred to as INTRA-SEXUAL SELECTION
• Because of the huge parental investment for women and because women have a limited time frame for reproduction, being promiscuous would not make sense. Instead, it pays for women to be particularly choosy and select the ‘best of the pack’ to have their offspring with. This means that women end up being the selectors – this strategy is referred to as INTER-SEXUAL SELECTION.
• Inter-sexual selection – is between the sexes, the strategies that females use to select males. Preferred strategy of the female to select the ‘best of the pack’.

  Intra-sexual selection – is within each sex, such as the strategies used within a group of males to compete with each other to be the one that is selected. Preferred Strategy of the male.
• Evolutionary theory of Partner Preferences

  What men/women look for: It also follows that there will be differences in what males and females find attractive in a mate, to ensure their genes have the best chance of being passed onto the next generation
• Males tend to look for signs of ‘fertility’ (i.e. mating with a female who is already pregnant or no longer fertile would be a waste of reproductive energy). Signs of fertility in women include: big eyes and lips which represent youth, waist to hip ratio of 0.7 which shows the female is not currently pregnant and facial symmetry which suggests strong genes, as well as nurturing characteristics. (Although males are overall much less choosy due to the reasons explained above!
• Females look for features such as strength, facial symmetry, height and ability to protect and provide for her and her offspring, as these features ensure good genes and that the child will survive. The ‘sexy sons hypothesis’ suggests that a female will choose a male with desirable traits, so that this ‘sexy’ trait is passed on to her son – meaning that he is also likely to be selected by other females and ensuring that her gene line will continue.
• Because those males with these features are more likely to be sexually selected by women, this has led to Sexual Dimorphism – the differences in characteristics between males and females. Males are generally larger and more muscular than females. Evolutionary psychologists would argue this is a gender difference that has developed over successive generations because it was only these muscular males who were sexually selected by females to mate with, and so only their genes have been passed on. Women are not as muscular because this is not seen as a desirable trait by males.
• Female choosiness was illustrated by Clark and Hatfield (1989). They asked male and female student volunteers to approach opposite sex students individually on a university campus, asking the same question: ‘I’ve noticed you around the campus. I find you very attractive. Will you go to bed with me tonight?’ They found gender differences in the responses: 75% of male students agreed; however, 0% of females said ‘yes’. This is fully in line with the ‘anisogamy’ and ‘parental investment’ idea that females should be more ‘selective’ in their choice of mate, yet males cannot afford to be as choosy.
• Differences in partner preference were demonstrated by David Buss (1989), who surveyed over 10,000 adults in 33 countries. Buss found that females universally put more importance on resource-related characteristics in a partner, such as ambition, high intelligence and good financial prospects. Males, however, preferred younger mates and put more value on signs of fertility, such as WHR. This supports the theory that males choose a mate based on fertility characteristics whereas females look for characteristics to protect them and the offspring longer term again in line with evolutionary ideas.
• Further evidence comes from research carried out by Devindra Singh (1993, 2002). She studied the measurements of waist-to-hip ratio of the winners of the Miss America contest for a decade and found that men generally found any waist and hip sizes attractive, as long as a ratio between them is about 0.7. A female having larger hips and a slim waist achieves this ratio, and men unconsciously interpret this as a sign that the woman is fertile but not currently pregnant. Therefore it could be that men have evolved to find this feature attractive in order to give their genes a survival advantage.
• Evolutionary explanations ignore social and cultural influences. For the past 100 years, Western societies have experienced significant changes in terms of gender equality and women’s independence. These changes mean that women in modern Western societies may no longer be looking for a man to provide them with resources; and other qualities in a mate become more important.
• Kasser and Sharma (1999) found in their analysis of 37 cultures that females mostly valued a mate with resources in societies where women’s access to education and workplace was severely limited. This makes evolutionary explanations limited, as they only explain human mates’ choice in terms of

  evolutionary adaptiveness, ignoring other important factors, such as culture and social norms
• Most of the studies into females’ choice of mates were carried out on undergraduate students. As these women were expected to achieve a high education status leading to a secure income, their preference for high-status men may stem from a desire to have a mate with similar interests to themselves, rather than a desire to have a mate who is a provider.
• Furthermore, research into evolutionary explanations also may suffer from a problem of validity, in terms that it is measuring expressed partner preferences rather than real-life ones. This is a problem as if the supporting evidence for a theory lacks validity (is inaccurate) then this evolutionary theory of partner preferences may not be as credible as it first seems.