Lecture 4 Flashcards
Define parental investment
Increasing the chances of your offspring’s survival and reproduction at a cost to your ability to invest in more offspring.
Discuss parent-offspring conflict out of the womb
There is a conflict of interest because the parents prioritise their offspring equally, however, the offspring prioritise themselves and want to be prioritised because they are more related to themselves than they are to their siblings/half siblings. There is also conflict because the parents want to stop investing in their child at a younger age than the offspring want. This is because it become more costly than beneficial as the child is able to be self sufficient meaning the parents could be investing in another child. However, the child wants to be cared for for longer as it will increase their fitness further.
Discuss parent-offspring conflict in the womb
The mother has to invest in her foetus massively, however, the foetus wants full investment for itself and none for siblings. Because this investment is so high, it has been theorised that spontaneous abortions occur to ensure the foetus is of good quality. Initially, the mother supports the implantation of the embryo, however, the embryo must then produce hCG to prove it is of good quality. Otherwise, it will be aborted; sometimes it pays to sacrifice opportunities. This can cause conflict because the embryo and mother may have different cut off points. There’s 3 sets of genes within the placenta and embryo; the mother and offspring mixed, the father’s and the mother’s. The paternal genes demand the most calcium from the mother’s blood as they aren’t affected if the mother cannot produce further offspring. When in calcium stress, the mother turns off these genes to ensure she can produce further offspring resulting in a conflict of interest.
There’s also paternal-maternal conflict in terms of blood pressure. When the embryo is early on, the mother controls the blood flow to it to counter the effects of high blood pressure later on. In late pregnancy, the mother can get high blood pressure because the paternal genes control growth rates and therefore increase the blood flow to the foetus causing conflict.
There’s also parent-offspring conflict in terms of morning sickness. Some argue that it occurs to protect the foetus from harmful substances like meat and alcohol. However, it is also argued that it’s foetus driven; if the mother is sick then she has reduced energy levels. This increases her insulin levels which suppresses her tissue synthesis. A lack of tissue synthesis will mean that more energy can be used up on the foetus.
Do parents invest in their offspring equally?
No. There are parental biases meaning that they invest most in the child that is most likely to give the best fitness returns. Also, there is sibling rivalry as they want the maximum parental investment. Parents also have teaching biases where they encourage traits with the best fitness advantage, for example, boys are taught to be strong and competitive and girls are taught to be restrained. This is an example of phenotypic plasticity. However, it needs to be understood that teaching biases are sensitive to culture.
Due to sibling rivalry, each sibling fills its own niche in order to get the maximum investment it can. First born are usually power driven; they exploit parental investment whilst they are an only child and then they control later siblings. Later siblings are more creative meaning they can be flexible in exploiting parental resources. Also, later siblings are less likely to name their parent as the closest person as they have had to invest in non-kin alliances to improve their fitness. This shows how personality can form in order to maximise fitness.
Discuss investment in relation to infanticide
This can be described as scheduled investment so that the parents can invest in future options. Infanticide is most likely to occur when their is paternity uncertainty, poor infant quality or a lack of resources. If women are highly reliant on male investment then mother infanticide can occur if there is paternity uncertainty, to ensure that the male wants to invest. Infanticide is more likely to occur with twins as well because it can cause poor infant quality; poor health, increased stress for mother and a reduction in the mother’s fitness. Also, if there is a lack of resources then infanticide can occur because it would be better to invest in the future. For example, infanticide is more common among single mothers.
Discuss the Trivers-Willard effect in relation to investment
The Triver-Willard effect argues that parents invest in male offspring more when they are in good condition and females when in bad condition. This is because males need to be in good condition to reproduce so if you cannot provide that for them then you shouldn’t waste resources on them. You should, however, invest in a daughter when resources are low because they pick the males so it doesn’t matter as much what condition they are in. This only occurs when there are differences in a mother’s access to resources in a population and if one sex in the population has greater variance in reproductive success. The TWE results in sex ratio biasing and resource allocation biasing. This is explored by looking at the biasing and assessing the outcomes of parents in different conditions.
Give 3 examples of sex ratio biasing and 1 example of resource allocation biasing
- Rajputs; they have a stratified class system where hypergyny occurs meaning women marry men from the class above them. However, this means that higher class females have less options, resulting in parents investing in sons more. Female infanticide was very high in this culture before the 20th century.
- Mukogodo; this population is of a lower class than their neighbouring population. This meant that the women had lower bridal prices, making them more attractive than expensive women but it also meant that men were neglected more. This is apparent when you look at sex ratios and hospital visits; when women in this society were sick, they were taken to hospital more often than when the men were sick.
- Inuit; their sex ratio was biased in favour of men as the hunting was high risk so the population needed men in order to survive. The children were named by the community and if they were unnamed then they were left on the ice, this was to prevent free riders. It’s an example of group selection and can be explained via evolution as it gets rid of the selfish members of the society.
- Their have been studies that have found that when women are in the breastfeeding stage, they don’t ovulate. This is to ensure they don’t get pregnant as they wouldn’t be able to prioritise their resources to their newborn child.
Discuss Haig’s study
They found that infants have more wakefulness in the night in the second half of their first year. It was hypothesised that this was because it prolonged the amount of time lactating, thus prolonging the onset of the mother’s menstrual cycle. This means that the baby gets longer without a sibling and can therefore exploit the mother for resources for longer.
Discuss Gangestad’s study
They found that the placenta releases CRH which increases the release of maternal cortisol. This release of cortisol increases the mother’s release of glucose meaning more energy for the foetus. However, cortisol is harmful for the foetus so the mother has co-evolved to become less sensitive to cortisol in the HPA axis in order to protect the foetus. This shows the conflict of interest between the mother and foetus as the foetus wants higher levels of glucose and expects the mother to deal with the cortisol consequences but the mother wants lower levels of cortisol to protect the baby and in turn glucose.
Discuss Nitsch’s study
They explored sibling rivalry and found that it only occurred among same sex elder siblings. Same sex elder sibling reduced the fitness of their younger siblings as they are competition in terms of finding a mate. However, opposite sex elder siblings increased the younger siblings’ fitness, presumably because they aren’t any competition.
Discuss Schnettler’s study
Discuss Kolk’s study
They explored the sex ratios among billionaires and did not find support for the Trivers Willard effect as the population of males was the same as the U.S. average.
They also found no evidence for the Trivers Willard effect. They examined over 3 million births in relation to socioeconomic status. Not only was the sample size massive, but they also explored various aspects of socioeconomic status like income, parental wealth, educational level etc. There was absolutely no correlation between any of the variables.
