Relationships: sexual selection and human reproduction

Question 1

what is natural selection?

Answer 1

• The individuals with characteristics that are most suited to the environment are more likely to survive and reproduce whilst those without these characteristics will die off.
• The genes that allowed the individuals to be successful are passed onto the offspring.

Question 2

What is sexual selection and the evolutionary approach

Answer 2

• if a characteristic increases the chances of reproduction then the characteristic will be adaptive/desirable because the animal will have more offspring.
• the selection of characteristics that increase mating success.
• evolutionary approach: the extent to which the (desired) behaviour/trait enhances the survival and reproduction of the individual’s genes.

Question 3

what is anisogamy?

Answer 3

• In anisogamous species, females invest more in reproduction than males -> results in 2 types of sexual selection:
  
  • INTER-sexual selection
  • INTRA-sexual selection

Question 4

what is inter-sexual selection

Answer 4

• (preferred choice of females) This is where one sex chooses traits they desire in the other sex – this selection is between the sexes.
• quality over quantity.
• preference of one sex, determines areas in which other sex must compete.
  -> peacocks: plumage
  -> Humans: eco resources, genetic fitness.

Question 5

what is intra-sexual selection

Answer 5

• Intra-sexual selection: (usually males) competition between members of same sex – this selection is within each sex – quantity strategy (indiscriminate)
• quantity over quality.

Question 6

what is the sexual strategies theory (SST)

Answer 6

• mating strategies that both males and females adopt under different circumstances.
• differs from previous theories in that it includes multiple motives each individual can have, such as short-term versus long-term mating.

Question 7

give 2 examples of female strategies for inter-sexual selection

Answer 7

• Fisher’s sexy sons hypothesis
• Zahavi’s handicap hypothesis

Question 8

what is fisher’s sexy sons hypothesis

Answer 8

• A woman chooses a man because he has a characteristic she wants (e.g. Tall male)
• Any male children she has will inherit this and will be more desirable to women.
• Over generations the characteristic becomes more pronounced – this is known as the runaway process.

Question 9

what is zahavi’s handicap hypothesis

Answer 9

• woman chooses a man with handicaps because it shows his ability to thrive despite handicaps, demonstrating genetic superiority.
• E.g. females finding males attractive who drink or take drugs in large amounts – demonstrates an ability to handle toxins, a sign of genetic fitness.

Question 10

What is sexual dimorphism?

Answer 10

• a result of mate competition.
• winners get to mate and pass on their genes. Whatever traits lead to success in these same-sex contests will be passed on to the next generation.
• Sexual dimorphism concerns the different characteristics that males and females possess:
• Males on average 12 – 15% larger than females.
• Males > deeper voice, facial hair
• These increase the chances of survival into adulthood and sexual maturity, where genes are passed to the next generation.

Question 11

Give 2 male strategies in intra-sexual selection

Answer 11

• sperm competition
• sneak copulation

Question 12

explain the sperm competition in intra-sexual selection (male strategy)

Answer 12

• Physical size matters for men.
• Behaviourally - aggression could work.
• Compete by producing bigger ejaculations and faster-swimming sperm.

Question 13

Explain sneak copulation in intra-sexual selection (male strategy)

Answer 13

• Males mate with females other than their partners if given the chance, as it increases their chances of reproductive success.
• Women gain from this by having a wider genetic diversity to their children, increasing survival chances.
• Women can also gain by being in a relationship with a resource-rich male, while copulating with a genetically fit stud.

Question 14

What is Cartwright’s theory on sexual selection

Answer 14

• both men and women prefer symmetrical faces.
• symmetry equates with reproductive fitness.
• also stated that women with symmetrical breasts are more fertile.
• supports concept that physical attractiveness is driven by increased ability to reproduce (evolutionary explanation).

Question 15

what are the evaluations for sexual selection?

Answer 15

positive:
- research support (Buss: what do women want?)
- Singh: curves in the right places

negative:
- explanation ignores social and cultural differences
- oversimplified explanation

Question 16

(+) Explain how Buss’s study ‘what do women want?’ supports sexual selection

Answer 16

• large cross-cultural study into human mating preferences -> 10,000 people, (33 countries).
• Found consistent sex differences.

Females want:
- tall and strong
- symmetrical face and body
- good financial provider

males want:
- chastity
- Healthy and physically symmetrical
- younger than me

Question 17

(+) explain how Singh’s study ‘curves in the right places’ supports sexual selection

Answer 17

• identified waist-to-hip ratio (WHR) as a universally major determinant of attractiveness.
• Used data from past 50 years of beauty contest winners and Playboy centrefolds.
• Small waist and full hips consistent desired feature.
• Optimum WHR = 0.7 (associated with fertility).

Question 18

(-) Explain how the explanation for sexual selection is oversimplified

Answer 18

• evolutionary explanation presumes heterosexuality and that all relationships are sexual
• cannot explain couples choosing not to have children, as it assumes all relationships are motivated by a desire to reproduce.

Question 19

(-) explain how explanations for sexual selection ignore social and cultural influences (Bereczkei)

Answer 19

• Partner preferences over the past century have been influenced by rapidly changing social norms of sexual behaviour.
• cultural factors such as availability of contraception.
• E.g. Bereczkei et al. 1997 - women in the workplace do not depend on men -> no longer resource-orientated.