Evolutionary explanations of Human reporoductive behaviour Flashcards
Describe the relationship between sexual selection and human reproductive behaviour
Sexual selection refers to the way that competition for mates between individuals of the same sex affects the evolution of certain traits. an example of this may be in the relative hairlessness of human bodies. this is a feature of humans which has become more pronounced over time, possibly because less hairy individuals are more attractive to the opposite sex and so have greater reproductive success. Pagel and Bodmer - put forward the view that hairlessness would have allowed humans to advertise their reduced susceptibility to parasitic infection (hairless skin is easier to keep clean). This trait therefore became desirable in a mate and led to the gene for hairlessness being more prevalent in future generations due to sexual selection. Similarly, studies of human mate preference have shown that men from a wide range of cultures find the hourglass shapeof young women attractive. this makes sense when applyinh the sexual selection theory because this shape is an indication of fertility in women.
There are two types of sexual selection - intrasexual and intersexual selection. the usual arrangement is for males to compete with other males for access to females (intrasexual selection leading to qualities such as strength and height in males) and for females to choose males they consider worthy as mate (intersexual selection which may also promote similar qualities). Women are looking to choose men with good genes which will be passed on to the women’s offspring, ensuring the offspring’s survival and their attractiveness to future mates, and so many grandchildren. This is sometimes known as the ‘sexy sons hypothesis’.
Discuss research into sexual selection and human reproductive behaviour
Montoya - has shown that females are attracted to males with masculine features such as a large jaw and prominent cheek bones. these features occur as a result of high levels of testosterone and this helps to indicate dominance and strength to females.
Buss - has shown that women in all cultures prefer men with resources or characteristics that would translate into resources in the future e.g. ambition, intelligence. This clearly supports the idea that females seek a partner who will be able to materially support a family. Males prefer women with child-like faces (big eyes, small noses and full lips) because these indicate fertility.
Describe the relationships between sexual selection and human reproductive behaviour in terms of mating strategies.
Sexual selection should lead to differences in mating strategies in men and women, as well as the differences in partner qualities described above. Men should want to be promiscuous because their reproductive success is determined by providing many offspring (quantity rather than quality). Women, however, should be more choosy (as they have limited reproductive potential and their investment in any child conceived is bound to be high) and therefore less interested in casual sex. they need to ensure they choose good quality men to produce good quality offspring.
Discuss research into the relationship between sexual selection and human reproductive behaviour in terms of mating strategies
Clark and Hatfield - support idea since they found far more males than females agreed to casual sex.
Further support for the evolutionary theory comes from the significant degree of cross-cultural agreement in ratings of facial attractiveness. This shows that criteria for facial attractiveness are not determined by cultural conventions and so lends support for the evolutionary theory which suggests these preferences are genetic, and so should apply across all cultures.
Evidence for females attempts to maximise their own reproductive success comes from penton-voak’s research which found women’s preferences for masculine features change according to where they are in the menstrual cycle. women were more attracted to masculine features in males when the women were ovulating and fertile, but more attracted to feminine features the rest of the time. This may indicate that a less masculine man may make a better long term partner (being seen as more kind and co-operative) but that women may benefit from being unfaithful when there is the highest chance of conception, in order to access genes which will provide the strongest healthiest (and sexiest) children.
Evaluate the evolutionary of theory of sexual selection and human reproductive behaviour
A limitation with much of the research documenting sex differences in mate choice is that it has focused on stated preferences rather than on real life choices. For example, personal dating ads support evolutionary ideas, with men requesting young attractive women and women requesting financially secure men. People may ideally want an intelligent ambitious partner but in reality may have to settle for less. However, studies of actual human behaviour have also supported evolutionary predictions e.g. men do choose younger women and if they divorce and re-marry they often choose women that are increasingly younger than themselves, supporting evolutionary theory.
Evidence which challenges the evolutionary explanation of sexual selection and human reproductive behaviour is that there are cultural differences in testicle size in humans. Measurements made during autopsy shows that testicle size in two Chinese samples were approximately half the size of testicles in a Danish sample. This provides evidence against evolutionary theory - which would have predicted similar sizes in human testicles because of similar pressures across the species in terms of sexual selection.
There is also a problem of gender bias in evolutionary theory as it has given men exclusivity for being promiscuous and this may ignore the benefits of promiscuity for females e.g. producing genetically diverse or better quality offspring, as suggested by penton-voak’s study. It is certainly not the case that females are always faithful and males always unfaithful, therefore this theory exaggerates differences between male and female behaviour as well as perhaps seeming to excuse such stereotypes, which is socially sensitive. Indeed, Nicolson argues that the relevance of evolutionary factors has been overemphasised and that modern relationships are not based solely on maximising reproductive potential as this theory suggest. She argues that relationship decisions are more likely to be made on a whole range of issues such as compatible interests and sense of humour. Therefore the theory is oversimplified and evolutionary influences on human reproductive behaviour are probably lost in today’s social context.
Discuss sex differences in parental investment - Maternal investment
Trivers - Defines parental investment as any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the costs of the parent’s ability to invests in other offspring. In most species, male and female parents do not invest in their offspring equally.
Maternal investment - Female investment tends to be greater because females have fewer eggs than males have sperm, and each egg is much larger, rarer and so more precious than each sperm. A female can only have a limited number of offspring, whereas a male can have a potentially unlimited number of offspring. So females invest more in their offspring and therefore have more to lose if they choose poor quality partners, so they have become more choosy. Females start investing in their offspring whilst they are still in the womb as the baby will be using nutrients supplied by the mother in order to grow and develop.
The female must carry the developing foetus for nine months and even after the birth the infants of early humans would have been dependent on their mother’s milk for several years. Breast feeding means that females are more obliged to look after their young, and that a mother will not become fertile again for many months or even years after conception. This further limits her reproductive potential (and this is clearly not the case in males) and so means she needs to be more choosy.
Another important reason for higher maternal investment in humans could be because of internal fertilization and the fact that females give birth. This means females can be certain that they are the biological mother to their offspring and so their investment will not be wasted.
Discuss sex differences in parental investment - paternal investment
Males do not have the same degree of certainty of paternity of their offspring. The great vulnerability for men is that they may use up valuable resources rasing children who are not their own (cuckoldry). Sexual jealousy in males may have evolved in response to this problem. due to the risk of cuckoldry, men are more jealous of the sex act, whereas women are more concerned about the shift of emotional focus (and consequent lack of resources) towards another woman. Males are not obliged to onvest more in each child than the energy it takes to have sex, and as males have virtually unlimited reproductive behaviour and may quickly conceive further children, their strategy is often described as ‘quantity rather than quality’. It therefore follows that each individual child will be relatively less important to them and so it makes sense that they will invests less than mothers do.
Discuss research evidence and AID sex differences in parental investment.
Research evidence does support the view that sexual jealousy is different in males and females- possibly due to the different fears faced by males and females (of cuckoldry for men, and lack of material support for women). Buss found that males were more upset at the thought of their partner having a physical relationship with someone else, (and showed greater galvanic skin response) whereas females were more upset at the thought of their partner having a deep emotional attachment with another woman. This supports the idea that males have more to lose from their partner’s physical infidelity because of the risk of losing economic support from their partner if he cares more for someone else. This is consistent with the idea that males may invest less in their offspring because of this risk of cuckoldry. However, this research has been criticised with the suggestion that males show greater arousal to any sexual imagery, regardless of its content, so this study may not after all show strong support for evolutionary theory.
According to parental investment theory, males would be more likely to share resources with children they know are their own, and less likely to share with children with whom they do not share a genetic relationship. However a study by Anderson et al suggests that this is an oversimplification of paternal investment and males do invest in their children, even when they know that the children are biologically not theirs. Anderson found that men did not discriminate financially between biological and step children born to a current partner. This seems to be contradictory to the evolutionary theory. However, and example of the ability of the theory to explain apparently contradictory evidence, is the idea that interests of the male to impress females with their skills as carers, to show their value as a potential mate. This would convince women to mate for life and reduce female infidelity. This is an example of the lack of falsifiability of evolutionary theory. This means that it is less open to scientific investigation which is a problem for psychology as a science.
There is evidence that there are gender differences in readiness to invest in children. Geher - questioned male and female undergraduates in an American university and found little difference in their answers about willingness to invest in children, when asked to imagine if they had them. However, when asked to imagine situations such as having to cancel a work appointment to look after a sick child, males showed higher ANS arousal than females. This suggests that the difference between participants’ statements about parental investment and their actual parental readiness may be due to social desirability, and actually males are less ready to invests than females, despite their claims, so supporting evolution.
