Lecture 3

Question 1

Why do people get married?

Answer 1

Because they are in love; but this is a recently new idea. Other reasons include creating alliances, and reproducing to maximise fitness.

Question 2

Discuss the three marriage systems

Answer 2

Polygyny is one male with many women. Monogamy is where there is one male and one female. Polyandry is one woman with many men. These marriage systems vary between cultures and seem to be dependent on specific environmental and cultural influences. Polygyny is a common system in humans, and some argue that monogamy has to be enforced through laws in order to prevent concentration of power

Question 3

Why would a woman marry a married man?

Answer 3

Decision making model; suggests a woman can get more resources from a wealthy married man than a poor man. Also the polygyny threshold model; if female reproductive success is a function of male wealth a woman can do better as a better as a second wife of a richer man than a less richer man.

Question 4

Why aren’t cultures always polygynous

Answer 4

Low (1988): Measures of polygyny in humans, they found polygyny will only be favoured by women if there is a large difference between the quality of males. If resources can be monopolised and/or there are conditions that emphasise inequalities between men.

Question 5

What conditions makes polygyny more likely

Answer 5

More likely in inequal societies. Women will only be polygamous if there is a large difference between the qualities of males. When disease increases so does polygyny! It’s about the ability to survive.

Question 6

Who benefits from polygyny?

Answer 6

Wealthy men; monopolise a larger share of reproduction. Women; choice over who they marry.

Question 7

Who loses out from polygyny

Answer 7

The majority of men; excluded from reproduction. The first wife maybe, as it means the husbands resources are on the other wife.

Question 8

Discuss monogamy

Answer 8

Monogamy = less crime, as polygyny is related to an increase in crime - maybe because men need more resources. Monogamy is related to more investment in children from father; polygamous males are too busy looking for their next mate. Monogamy increases a woman’s power.

Question 9

Discuss how matrilineal vs patrilineal inheritance

Answer 9

In a polygamous society it makes more sense to leave wealth to sons as they need it to attract wives (patrilineal inheritance) (Hartung, 1982). BUT interests of mother and father are not always the same; mothers fitness would benefit from wealth by investing in her sons only, whereas fathers fitness would benefit from wealth by buying more wives.

Question 10

How does matrilineal and patrilineal inheritance explain the oedipus complex

Answer 10

Hartung (1982), Freud thought that conflicts arose between fathers and son’s about sexual access to mother. Hartung suggested this is not about the mother but rather that sons and mothers are both supportive of the sons polygymy and opposed to the fathers. So theres still a sexual competition between father and son, but not for the mother. Also highlights the potential fitness benefits to women in polygamous society - polygamous sons.

Question 11

What is matrilineal inheritance

Answer 11

Wealth passed down maternal line - usually from man to sisters sons. Why? It is traditionally thought to result from paternity certainty. But just how low would paternity certainty have to be? If paternity certainty is that low (r<0.25) a man may not be fully related to his sister. But if you consider affect of paternity certainty on female line over many generations, then a small uncertainty can have an affect, combined with effect on male fitness, this could explain its prevelance

Question 12

How are marriage patterns related to incest?

Answer 12

Reproduction between close relatives increases the likelihood of exposing recessive conditions.

Question 13

How do we avoid incest?

Answer 13

Incest taboos; enforced laws. There are 3 sets of rules: True incest laws; close kin, Extended incest laws; to prevent lineage concentration and families becoming too powerful, and affinal kin; laws to prevent marrying in-laws.

Question 14

Can we see incest in animals?

Answer 14

Evolutionary interpretation; Westermarck effect; Mechanism triggered by proximity etc.

Question 15

What is Kibbutzim marriage

Answer 15

Communal farms in Israel, where children raised in peer group rather than by parents. Of 2769 marriages, none were between members of a peer group.

Question 16

What did Mace and Holden (1996)

Answer 16

Matrilinerally common in horticultural societies, rare in pastoral societies. Men may prefer a roving strategy of mating when they cannot monopolise resource

Question 17

What is the evidence for incest?

Answer 17

Affinal incest laws are more extensive in patrilocal societies vs matrilocal societies; greater opportunities for adultery, reduced paternity certainty. Punishment is more extensive

Question 18

What are the three rules of incest laws?

Answer 18

True incest; close kin.
Extended incest laws; prevent lineage concentration and families becoming too powerful.
Affinal kin; laws to prevent marrying in laws (adultery prevention?)

Question 19

Do the findings of Shepher (1971) and Wolf (1995) explain incest as an idea that doesn’t exist?

Answer 19

No. Because 44% of societies still have laws to prevent incest! This number is too much is incest avoidance is automatic.

Question 20

Discuss the study of Wolf, 1995

Answer 20

In Taiwan, there are minor marriages where very young girl is adopted into a house to marry a son, or major marriages where a girl is bought into a house after puberty to marry a son. There found that fertility rates are more than 25% higher in major marriages, and divorce rates are 2.5 times higher in minor marriages.

Question 21

What conditions may cause polyandry to happen

Answer 21

Traditional evolutionary explanation suggests there is a unique solution to a improverished environmental situation. Where men are limited in ability to support wives/offspring so a woman will have multiple husbands with different tasks and have children with all of them.

Question 22

Give an example of polyandry

Answer 22

In Tibet, where there is large farms at high altitudes men have poor productivity and it is not viable to split the farm into smaller units but there is a high demand for labour. Therefore fraternal polyandry is an economic solution.

Question 23

In terms of Hamilton’s rule, why would men share a wife?

Answer 23

Assume two brothers are in a polyandrous relationship; it means they are both related to each others children as well. The mean number of offspring in monogamy is 3.1, whereas mean offspring under polyandry is 5.2. The senior brother W(m) = 3.1, and W(p) = 0.5(5.2) + 0.25(5.2) = 2.6+1.3=3.9. However, does not work if we consider all forms of polyandry separately and assumes junior brother will get no offspring otherwise. Senior brother does worse under polyandry, and junior brother does well as his options are limited. Parents do better under polyandry and women do better under polyandry. Paternity skew of 69% would make polyandry adaptive for senior brothers, 98% could still be adaptive for junior brothers.

Question 24

What makes a marriage break down in polyandry relationships?

Answer 24

Economic opportunities for the younger brothers (elder brothers have greater reproductive access). This allows them to pursue monogamous marriages, but they may have to pay a larger economic price.
Number of brothers; as reproductive competition increases, more likely to split and birth-order negatively correlated with number of children.

Question 25

How do women manage a polyandrous marriage?

Answer 25

Makes reproductive sense for them to stay in polyandrous marriage. May not be about what is adaptive but about what is economically viable.

Question 26

Summarise this lecture

Answer 26

Main theme is the complex interaction between culture and biology - cultural rules/laws help serve the interests of lineage survival and inclusive fitness.
Cultural practices that define marriage and inheritance laws are consistent with evolutionary theory. Patrilineal inheritance is associated with polygyny. Incest rules may reflect patterns more so than inbreeding avoidance. Suprising practices such as polyandry could be explained as the result of adaptive conflicts of interest, or non-adaptive economically driven cultural decision.

Question 27

What did guttentag 1983 find in the study too many women? The sex ratio question

Answer 27

The number of opposite sex partners potentially available to men or women has a profound effect on sexual behaviours and marriage/divorce patterns.

When women are scarce they are surrounded by a protective morality that favours monogamy. Men need to find a woman, even just one as there isn’t as much choice.

When men are scarce, protective morality surrounding women dissolves and men become reluctant to make a lifetime commitment.