Sexual selection Flashcards
Explain Darwin’s view on sexual selection.
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. Any physical trait that enhances reproductive success will gradually be passed down and enhanced over evolutionary 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.
Explain Zahavi’s ‘handicap principle’.
Zahavi also proposed the “handicap principle” in support of sexual selection stating if any indicator is too costly to produce and is still displayed – it must be a sign of strong genes and health. As peacocks are able to display such bright, heavy features and still survive - this may make them more attractive to females and such “rules” may apply to humans.
Why are there gender differences in sexual selection?
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 favors them maximising 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.
What are the two types of sexual selection?
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.
Explain intra-sexual selection.
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 however 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 maximises reproductive success for them.
Explain intersexual selection.
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.
What has Buss et al found?
Buss et al conducted a cross-cultural study over 37 cultures with over 10’000 people on mate preference. Males reported to prefer younger physically attractive females while females sought physically strong and athletic males with an emphasis on resources. Both are therefore engaging in behaviour that increases reproductive success supporting sexual selection theory.
Criticisms of Buss’ study?
The main issue with this research was that questionnaires were used which can be easily mis-understood across cultures. Also self-reports may be inaccurate as well as translation problems occurring through the use of third party translators. Also mate preference may not be indicative of what actually happens either in real life.
What has Dunbar et al found?
Dunbar et al conducted a study looking at 4 american newspapers with over 900 personal ads reviewing mate preference. Women offered youth and physical attraction while men offered financial status and resources. Each sought what the other wanted supporting sexual selection theory.
Criticism of Dunbar et al’s study?
The issue here was this study was based only on americans which would mean it suffers from cultural bias. In addition kindness and intelligence was rated higher in importance from both sexes which was doesn’t fully fit in with sexual selection theory.
What did Thornhill et al find?
Thornhill et al found that symmetrical faces were sought by both genders and that symmetry was a sign of strong genetic fitness and strong resistance supporting sexual selection theory. Women also sought men with masculine features while men preferred women with childlike features such as large eyes, small nose, good teeth and full lips - all indicators of youth and fertility. Again both genders engage in behaviours in these studies that increase reproductive success.
Further criticisms of the theory?
- A big criticism of the theory is that it is not scientific and based almost completely on post-hoc evidence. Sexual selection theory cannot be proven or disproven either way and Popper argued that unscientific theories are purely speculative.
- Such theories also show gender bias as they assume men are more likely to cheat on their partners and points to genetic programming as the cause. This is not possible for men without “willing” females nor do all men cheat either despite this being their most ideal strategy. The theory cannot also explain why some women actually then cheat on their partners as this goes against their ideal mating strategy involving securing a single mate who can provide support and security over the long-term. “Cuckoldry” is provided as a possible reason for this but again this is post-hoc and difficult to prove/disprove.
- . Evolutionary theories such as this can be argued to be reductionist as they simply put down mate choice due to our genetic makeup. In truth partner choice is much more complex involving cultural and social elements which are not fully considered and this theory portrays us as driven purely by nature which is clearly not true.
Name all the researchers in this section.
- Buss
- Thornhill
- Dunbar
- Zahavi
- Darwin
