Lecture 5 Flashcards
What is parental investment
Any investment by the parent in an individual offspring that increases the offspring’s chance’s of surviving; at the cost of the parents ability to invest in other offspring
What is parent-offsrping conflict
Parents want to invest in lots of offspring, but offspring have to put themselves first. Parents are equally related to all their offspring (r = 0.5), but offspring are always more related to themselves than their siblings.
What happens to parental investment as offspring gets older?
Parents want to stop! Costs in terms of future children outweigh the benefits of investing in current children. This might be because the current children are at an age where they can look after themselves more. There is also a point where offspring will want parental investment to stop; this is because the costs in terms of future siblings outweigh the benefits of investment in self.
Discuss the parent-offspring conflict in the womb
A mothers investment in each foetus is huge. The foetus is more related to itself than siblings, whereas mother is related to all equally. This gives the potential for conflict in level of investment mother should provide the foetus
How can we explain parent-offspring conflict in the womb?
- Spontaneous abortion
- High blood pressure
- Morning sickniss
Discuss spontaneous abortion
Up to 75% pregnancies are spontaneously aborted. The selection for good quality mother; implantation of embryo initially supported by mother, but the embryo must produce human chorionic gonadotrophin (hCG) to prevent being ejected. Haig suggests that ability to produce hCG is an honest signal of quality.
What is spontaneous abortion?
Miscarriage (usually until 20 weeks, then still birth).
Discuss what Haig (2004) concluded about spontaneous abortion
Womb conflict over calcium metabolism. Maternal-fotal unit contains 3 sets of genes. Mother + foetus shared, foetus only (father), mother only. Paternal genens demand more calcium from blood serum than other sets. Mother inactivates paternal genes in times of calcium stress
Discuss high blood pressure in terms of parent-offspring conflict in the womb
Women in late pregnancy can get high blood pressure. Can cause pre-eclampsia. It is caused by increased blood flow to foetus (controlled by foetus). Mother counters this by reducing blood pressure early on (when she is still in control). But Moore & Haig (1991) suggested that this might be paternal/maternal conflict, as paternal genes control growth rates
Discuss morning sickness in terms of parent-offspring in the womb
70% of women experience morning sickness during the first trimester. Profet (1992) argued that this functions to protect the foetus from harmful substances. (Meat, caffeine, eggs, alcohol). There is no morning sickness in meat-free cereal based diet societies, and babies are also bigger when mother has experienced morning sickness.
Is morning sickness mother drive or foetus driven?
Mothers have reduced energy intake compared to foetus. Which results in elevated insulin which suppresses mothers tissue synthesis - suggests this is more for the baby
Do parents love their children equally?
Perhaps; but parents can increase fitness by investing differentially in their offspring, depending on who is likely to give them the best fitness returns. This is called parental biases. And children should aim to maximise their parental investments. (sibling rivalry).
What is parental bias
Parents can increase fitness by investing differently in their offspring depending on who is likely to give them the best fitness returns
How can parents invest in the right baby
Parents may exhibit teaching biases, where certain traits are encourages in offspring in order to increase their fitness.
Discuss the findings of Low (1989)
Girls are encouraged to be restrained and chastle. Boys are encouraged to be strong and competitive. But these teaching biases are highly sensitive to culture - reflecting conditional strategies depending on mating systems
Discuss sibling rivalry
- First born conformist and power driven. They exploit advantage in parental attention and allows them to control later siblings. 2. Later born children are more creative, non-conformist. They are more flexible in exploiting parental resources.
What did Salmon and Daly (1998) find out in terms of sibling rivlary
Different interpretation of birth order effects. Younger children less likely to name parent as closest person. Opting out of competition altogether and pursuing non-kin alliances and more cooperative traits may be more likely in younger offspring
How can parents invest at the right time
Infanticide: highly emotive topic, but widespread and worthy of consideration. Infanticide can be considered scheduled investment, where reproductive attempts are abandoned in favour of future options.
Under what circumstances might infanticide be considered scheduled investment
Paternity uncertainty.
Poor infant quality.
Lack of parental resources.
Discuss paternity uncertainty in terms of infanticide
Evidence that men are wary of investing in another’s offspring; virgins at marriage, female circumcision, menstrual taboos, Babies likened to fathers appearance, detecting infidelity. Thus mothers infanticide might be a risk factor when women are highly reliant on male investment.
Discuss poor infant quality in terms of infanticide
Cultural taboos associated with some physical attributes, twins; poor health, stress on mother, ultimate fitness of mothers of twins lower.
Discuss lack of parental resources as a factor of infanticide
If unable to invest at the current time, wait for future opportunities; single women are more likely to terminate pregnancy unless they have reduced potential for future options
How might the sex of offspring affect investment strategies?
The trivers-willard effect (1973)
What is the trivers-willard effect?
If one sex has greater variance in lifetime reproductive output than the other, or if mothers vary in their access to resources then difference in preference for offspring of the two sexes should either evolve. When mothers have lots of resources, they should invest more in sons, when they have poor resources, they should invest more in daughters. This could result in a sex-ratio biasing or resources allocation biasing
How can you test the preference for boys or girls
- Assess parental biases.
- Asses reproductive outcomes of parents in different conditions.
But few studies do both, so how do you know that the parental biases result in increased fitness? Also, it is assumed that the two sexes have differential reproductive potential in different conditions.
Is their any evidence for parental biases in different sex offspring?
Sex-ratio biasing. Historical and anthropological studies
Discuss the findings of Rajputs (Indian caste)
- Rajputs; highly stratified society with patterns of hypergyny (women marry up the social strata), and females had fewer marriage options so sons were favoured. There was also explicit infanticide of female offspring pre-20th century.
Discuss The Mukogodo in sex ratio biasing
Hunter/gather society that was recently pastoralist. Poorer and lower class than neighbours, with women fetching low brideprice. Men are unattractive as husbands, with male neglect. 98 female children vs 66 male.
Discuss sex-ratio biasing in Inuits
Harsh environment, with high risk hunting. 19th century male biased sex-ratio (173 males, 100 females). Bias correlates with harsh conditions and hunting risks. Irwin (1989) found sex ratio is biased in order to prevent starvation. Observations were rare, but community traditions imply it could be common
What were the take home messages of this lecture?
Investing in offspring in order to maximise fitness is not always straightforward - sometimes it pays to sacrifice opportunities. Offspring always want to survive; so parent-offspring conflict can happen in the womb (morning sickness, high blood pressure, spontaneous abortion). Personality may be dependant on differential strategies to maximise fitness. Infanticide may occur as a last-resort strategy to maximise future options.
