Sexual Selection & Human Reproductive Behaviour.

Question 1

Evolution - Darwin:

Answer 1

• Darwin noticed evolution favours development of some feature that are attractive to opposite sex.
• Favourable features make it more likely for possessor to attract a mate and pass on their genes.
• Increased reproductive fitness central to evolutionary success.

Question 2

What does sexual selection explain?

Answer 2

Why some human characteristics provide advantage for human reproductive behaviour as they are attractive to potential males.

Question 3

What is natural selection?

Answer 3

Process whereby organisms better adapted to their environment tend to survive and produce more offspring. Survival of the fittest.

Question 4

What is sexual selection?

Answer 4

Involves natural selection of characteristics increasing reproductive success. Survival of the hottest. Evolutionary explanation of partner preference.

Question 5

Relationship between sexual selection and human reproductive behaviour:

Answer 5

Leads them to use different strategies to maximise their reproductive potentials.

Question 6

What is sexual dimorphism?

Answer 6

Refers to differences in size and shape between females and males of same species. Usually secondary sexual characteristics.

Question 7

Waist-to-hip ratio: Singh (1993, 2002)

Answer 7

• Studied evolutionary theory on partner preference in terms of waist to hip ratio.
• Males find any hip and waist sizes attractive that have ratio of 0.7.
• Combination of wider hips and narrower waist is attractive as it’s ‘honest signal’ the woman is fertile.
• Shows evolutionary factors reflected in patterns of human reproductive behaviour through partner preferences.

Question 8

What is anisogamy?

Answer 8

• Differences between male and female sex cells - gametes.
• Male and female sexual behaviour subject to different selective pressures.
• Reproductive success = production of healthy success.

Question 9

Consequence of anisogamy.

Answer 9

No shortage of fertile males, but fertile women are rare ‘resource’.

Question 10

Male gametes (sperm).

Answer 10

• Extremely small and highly mobile.
• Created continuously in vast numbers from puberty to old age.
• Do not require great expenditure of energy to produce.

Question 11

Female gametes (eggs).

Answer 11

• Relatively large and static.
• Produced at intervals for limited number of fertile years.
• Require huge investment in energy.

Question 12

Intra-sexual selection (male strategy).

Answer 12

Quantity over quality. Refers to competition of males to be able to mate with a female, winner of competition reproduces and gets to pass on characteristics that contributed to victory onto offspring.

Question 13

Inter-sexual selection (female strategy).

Answer 13

• Quality over quantity. Ova rarer than sperm and require greater energy to produce. Female needs to select partner who can provide resources and is genetically fit, so is choosy as doesn’t want consequence of making wrong choice.
• Female strategy is to select genetically fit partner who’s able and willing to provide resources.

Question 14

Trivers (1972).

Answer 14

Emphasises the female makes a greater investment of time, commitment and other resources before, during and after birth of her offspring.

Question 15

Fisher (1930): ‘Sexy Son’s Hypothesis’:

Answer 15

Women mate with males who have desirable characteristics and their ‘sexy trait’ is inherited by her son. Increases likelihood females will mate with her son. Attractive male offspring possess best chances of procreating and passing on mother’s genes to next generation.

Question 16

Strength: research support for inter-sexual relationship.

Answer 16

P: Research support for inter-sexual relationship.
E: Clarke and Hatfield (1989) – male and female students sent out across uni campus and approached other students with question: ‘Would you go to bed with me tonight?’ Not a single female agreed to this, 75% of males did.
C: Supports suggestion female choosiness and males have evolved different strategy to ensure their reproductive success.
I&D: Means evolutionary explanations more reductionist by today’s standard, should now take more holistic approach.

Question 17

Strength: research support for intra-sexual selection.

Answer 17

P: Research support for intra-sexual selection.
E: Buss (1989) tested p’s from 37 cultures, finding males prefer young, physically attractive females. While females prefer resource rich, ambitious males.
C: Supports sex differences due to anisogamy and partner preferences derived from sexual selection theory.

Question 18

Limitation: the relationship ignores social and cultural influences.

Answer 18

P: The relationship ignores social and cultural influences.
E: Partner preferences changed due to the influence of changes of social norms and sexual behaviour. Chang et al (2011) compared partner
preferences in China over 25 years - some had changed, others remained the same, corresponding with the huge social changes in that time.
C: Suggests both evolutionary and cultural influences must be taken into account when explaining human reproductive behaviour.