Lecture 14 - human reproductive behaviour

Question 1

why is the application of evolutionary theory to human reproductive behaviour a controversial area of research?

Answer 1

• cultural influences

- ethical difficulties of conducting experiments to test hypotheses

Question 2

what is evolutionary psychology (aka sociobiology)?

Answer 2

-The study of the effects the genes on human behaviour

Question 3

describe the controversies of sociobiology?

Answer 3

• Simplistic arguments over behaviours - hard to test
• Eugenics, apartheid, etc - originally thought to be scientific arguments - nazis etc - highlights differences between groups

Question 4

what is life history theory?

Answer 4

natural selection should synchronize senescence of somatic and reproductive functions

Question 5

what human function does not fit the life history theory?

Answer 5

menopause - loss of reproductive potential and long post-reproductive life

Question 6

How common is menopause?

Answer 6

extremely rare - only in humans and pilot and killer whales

Question 7

what are the 2 hypotheses to explain menopause?

Answer 7

1) mother hypothesis

2) grandmother hypothesis

Question 8

what is the mother hypothesis?

Answer 8

Avoid risky reproduction and

mortality in later life and ensure survival of existing offspring (own benefits)

Question 9

is there evidence for the mother hypothesis?

Answer 9

life history data on pre-modern Finns and Canadians shows that beyond the age of weaning, offspring fitness was not adversely affected by maternal death, presumably due to compensation by remaining family members

Question 10

what is the grandmother hypothesis?

Answer 10

Kin selection – gain inclusive fitness by helping existing offspring to reproduce (benefits to your offsprings offspring rather than own)

Question 11

what did the study on pre-modern finns find about the grandmother hypothesis?

Answer 11

the number of grand-offspring a woman has is correlated with her post-reproductive lifespan. The presence of a mother is associated with higher fecundity and higher Lifetime Reproductive Success of sons and daughters via earlier reproduction of offspring, shorter birth intervals and better survival of grandoffspring. These effects are most apparent when the grandmother is local (<20km away)

Question 12

why may the grandmother hypothesis not be the complete answer?

Answer 12

Kin-selected benefits of ‘helping’ don’t outweigh benefits of continued reproduction

Question 13

what did cant & johnstone suggest about menopause?

Answer 13

suggest menopause ALSO driven by reproductive competition between mother and daughters (in-law)

Question 14

are siblings helpers?

Answer 14

• Overall, fitness increased by older opposite-sex siblings, but reduced by older same-sex siblings
• so NO

Question 15

are aunts and uncles helpers?

Answer 15

no

Question 16

is their evidence of cooperative breeding in humans?

Answer 16

In general there is little or no evidence

Question 17

what do human mating systems depend on?

Answer 17

ecological conditions, as well as cultural influences

Question 18

describe polyandry in tibet

Answer 18

families involve one woman marrying several brothers

• 31% of females aged 20-59 were unmarried (not enough men to go around
• The effect of this polyandrous marriage system is a much reduced reproductive rate

Question 19

why does polyandry occur in tibetan buddhists and how is conflict avoided?

Answer 19

polyandry is ascribed to severe constraints on agricultural land. When resource base changes, polyandry is abandoned. Male conflict is reduced by kinship and age hierarchy among co-husbands - second son is often sent off to be in monastery

Question 20

monogamy is common but what interferes with monogamy?

Answer 20

• Extra-pair paternity

* Serial monogamy

Question 21

what is indicator of the frequency of extra pair paternity

Answer 21

the testes size compared to body size - humans have size that suggests low rate of extra pair paternity

Question 22

are their fitness benefits from serial monogamy?

Answer 22

• For males there appears to be a fitness increase with serial monogamy - more wives you have in your lifetime the more children you have - not the same for women - probably down to the existence of menopause

Question 23

describe polygyny in human societies?

Answer 23

often resource defence polygyny - e.g. wealthy high resource men have multiple wives -
Study of Kipsigis society in Kenya - mean number of reproductive wives correlates to the amount of area a man owns

Question 24

what did Currie et al find out about social evolution in human societies?

Answer 24

showed that transitions between social systems (defined by political complexity) follow predictable pathways, with sequential changes in complexity prevailing