Sexual Selection Flashcards
(32 cards)
Who came up with the idea of sexual selection?
Darwin
Explain what natural selection is
Darwin explained evolutionary change in terms of natural selection.
The process whereby organisms better adapted to their environment tend to survive and produce more offspring
–> A characteristic that increases an individual’s ability to reproduce successfully must be highly adaptive and those with these genes will go on to produce successive generations, whilst weaker genes will die out
What are the problems with natural selection?
Some species have evolved characteristics that are positively detrimental to their survival, such as stags’ antlers and peacocks’ tails
What did Darwin come up with after natural selection to overcome the problems?
Sexual selection
Explain what is meant by sexual selection
The evolutionary explanation describing why humans prefer some partners over others
Men and women attempt to maximise their chances of reproduction (since reproduction is more important that survival)
We consider what we need from the opposite sex
What is sexual selection
A key part of Darwin’s theory explaining how evolution is driven by competition for mates, and the development of characteristics that ensure reproductive success
What is sexual dimorphism?
The condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs.
The condition occurs in many animals and some plants.
Explain what is meant by sexual dimorphism?
- In many species, males have characteristics (e.g. brighter colouration or exaggerated tails) that serve to attract females.
- Suggests that males are competing for the attention of females.
- Suggests that, in many species, females do the choosing.
What is anisogamy?
- The difference between sex cells.
- A type of reproduction where gametes of 2 sexes are dissimilar (in terms of size and number).
- Important for partner preference as gives rise to 2 different mating strategies
Explain anisogamy in terms of humans
Males
- Produce millions of sperm
- Very little cost
- So their best strategy is to mate with as many females as possible to produce the maximum number of offspring.
Females
- Produce 400 eggs in a lifetime.
- Huge biological cost during pregnancy and breast feeding.
- So their best strategy is to be very discrimating and more selective as need good genes.
What is intrasexual selection?
- Mate competition
(i.e. between males for females). - Means the male who wins can pass his genes on to the next generation.
- Can lead to aggression (towards other men for a woman, and to women with child (bc of sex with others)).
- Male preference for youthful and fertile women (leads to reproductive success) and good hip:waist ratio.
What is intersexual selection?
- Mate choice
- The female is choosing which male to mate with.
- Women look for traits in a man that they want their son to have (sexy sons hypothesis)
Outline short-term mating preferences for sexual selection
- We possess a range of mating strategies evolved for short-term mating success.
- According to parental investment theory, men evolved a greater desire for casual sex, and would ideally seek sex earlier in a relationship.
What did Buss (07) say about short-term mating for sexual selection?
Over the period of a year, a man who managed to impregnate a large number of females would have passed on more copies of his genes than a less successful male - but female who had sex with the same number of males in a year is likely to produce only one child - the less time a man permits to elapse before he has sexual intercourse with a woman, the larger number of women he can impregnate in a given time
What did Buss & Schmitt (93) say about short-term mating for sexual selection?
In contrast to women, men appear to lower their standard in the context of short-term mating - they also show a marked decrease in attraction following sex - evolved adaptation to bring about a hasty departure which prevents them spending too long with one woman.
Outline long-term mating preferences for sexual selection
Both sexes typically invest heavily in any offspring so sexual selection favours high levels of choosiness in both sexes - as women have an obligatory biological investment in children, predicted to be very particular about their choice of mate, however males are also choosy.
What does Buss (03) say about long-term mating preferences for sexual selection?
Females are attracted to males who are able to invest resources, able to physically protect and show promise as a good parent
Name 3 evaluative points for sexual selection
+ Evidence supporting sexual selection pressures through evolution.
+ Evidence supporting the idea females are more selective.
- Evidence suggesting it’s incorrect that patterns still have strong evolutionary basis.
+ AO3 - Evidence supporting sexual selection pressures through evolution.
- Research by Singh (1993) suggests that there are some sexual selection pressures which have been
constant in terms of evolution and in terms of modern times
~ E.g. the hip to waist ratio - If this ratio is around 0.7, then this demonstrates to potential mates that
the female is fertile and able to carry children over a long period of time. - Birth easier when
the female has larger hips and a narrower waist. - Therefore, this suggests that some evolutionary
pressures are still relevant in modern times.
+ AO3 - Evidence supporting the idea females are more selective.
- Evidence by Clark and Hatfield (1989) supports the idea that females are more selective when it comes to
potential mates. - Due to their greater energy and genetic input into the pregnancy and care for the
child. - These researchers found that 75% of college
males, compared to 0% of females, would be willing to sleep with a stranger if this stranger had
approached them and complimented them! - This supports the idea that men have an evolutionary predisposition to want to impregnate as many women as possible.
- This due to the high rates of sperm
production and little energy/resources required to do so.
Also supports the differences in mate selection strategies used by females and males i.e. intra- and inter-selection.
- AO3 - Evidence suggesting it’s incorrect that patterns still have strong evolutionary basis
- Evidence by Chang et al (2011)
- Suggests it’s incorrect to assume current reproductive patterns still have a
strong evolutionary basis
~ an interactionist approach would be more accurate –> where the
influences of both culture and evolution are combined together. - Changing social and cultural norms means women no longer place a large emphasis on
resource-availability when looking for a new partner (as suggested by Bereczkei et al in 97).
~ women are now more financially independent, with the average age of marriage currently exceeding
30. - This suggests that some evolutionary pressures for inter-sexual selection no longer apply in the
modern climate.
Explain males’ preference for younger women for sexual selection
- More likely to be fertile
- Female reproductive value peaks and declines relatively early in life.
Explain mate-choice in real life for sexual selection
- Good waist:hip ratio
- Nurturing characteristics )to be good mother)
- Youthfulness (fertility)
- Good genes - symmetrical face
Collectivist cultures
- Chastity
- Domestic
Individualistic cultures
- Shared child care
- Less worried about chastity
Explain gender differences in short-term mating strategies for sexual selection
- Men generally relax their mate preferences in short-term mating, whereas women increase their selectivity in short-term mating, especially for physical attractiveness.
- Men also prefer short-term mates who are easily sexually accessible.
