Flashcards in Part 4 - Humans and Levels of Selection Deck (54)
One controversy associated with evolutionary psychology/sociobiology is that it is often reduced to very ... arguments, e.g. defined evolved gender roles.
It can be difficult or considered ... to carry out certain tests on human subjects - hard to gather useful data.
Another controversy that has arisen since the time of Darwin is the idea of .... Evolutionary theory has been used to justify ideologies such as ... and ....
eugenics, apartheid, nazism
A third controversy concerns .... When we exhibited certain behaviours we are not consciously considering its effect on our .... However, this is not true of any animal really (probably), e.g. a cuckoo chick pushing a reed warbler egg out of its nest is not considering its fitness benefits, they're evolved behaviours that do not need to be rationalised.
Why is menopause problematic?
Life history theory tells us that natural selection should synchronise the senescence of somatic and reproductive functions - why would the body remain functional long after reproduction stops?
What is menopause?
The loss of reproductive potential and long post-reproductive life
- not exclusive to humans - found in 2 other organisms - shortfin pilot whales and killer whales.
Menopause exists in every society, regardless of modern medicine. Across societies, the median age of a woman's last birth is .... The average age for menopause is .... This leaves a post-reproductive life of generally over 20 years.
Pilot whales have a median age of last birth of 36 (similar to our own), leaving 30+ years of post-reproductive life. Killer whales are longer lived, with a median age of last birth of ..., leaving up to ... years of post-reproductive life.
What are the main hypotheses for the menopause?
a) mother hypothesis - to avoid risky reproduction and mortality in later life and ensure survival of existing offspring
b) grandmother hypothesis - kin selection - gain inclusive fitness by helping existing offspring to reproduce
a) By collecting life-history data on pre-modern (before oral contraception and modern medicine) Finns and Canadians, Lahdenperä et al. (2011) found that ... of children beyond age 15 was not affected by the age at which their mother died in canada, and in finland there was only a reduction in lifespan if the mother died when the child was between ... years old (...-... age). In both populations, there was no effect of the child's age when the mother died on lifetime reproductive success.
So evidence suggests that, beyond ..., offspring fitness was not affected by maternal .... From this analysis, the mother hypothesis cannot explain the post-reproductive ... of human females.
lifespan, 0-2, pre-weaning
weaning, death, longevity
a) Why? It is likely ... for by other family members.
- capacity for compensation reduced prior to weaning as this requires maternal resources
b) Grandmother hypothesis - number of grandchildren should be correlated with...
Is this the case?
There is a strong positive correlation - on average there are 2 extra grandchildren for every 10 years post menopause (across Finnish and Canadian populations)
- supports grandmother hypothesis
b) found that a living grandmother was associated with:
- higher ...
- higher ...
- earlier ...
- shorter birth ...
- increased survival to ...
Only if grandmother was ...
Younger grandmas had more of an effect.
do not have the same effect - non-significant effect on lifetime reproductive success of daughters.
Cant and Johnstone (2008) argued that the grandmother hypothesis is not the complete answer. This is because...
the kin-selected benefits of helping do not outweigh the benefits of continued reproduction.
They suggest that menopause is also driven by...
reproductive competition between mother and daughters (and daughters in-law)
Lahdenperä et al. (2012) also tested this hypothesis in their Finnish population. They found that there was very little overlap, at the population level, between the production of ... and the production of ..., i.e. mothers and their daughters very rarely overlap in their production of offspring.
Overlap of a mothers offspring with her daughter-in-law's offspring...
reduced the survival of 1st and 2nd generation offspring (no effect when mother and daughter overlap reproduction)
So a combination of the ... effect and reproductive ... between mothers and their daughters ... ... seems to provide a good explanation for the occurrence of menopause in humans.
There is evidence that similar processes are at play in the whales in which we observe menopause.
grandmother, competition, in law
Are humans cooperative breeders?
Assessing Finnish populations again (Nitsch et al, 2013), a positive effect of...
number of elder siblings on survival to sexual maturity was found (particularly true of males and elder brothers on females)
- not a significant effect of number of elder sisters on female survivorship
However, the number of elder same sex siblings an individual has has a negative effect on....
This may be because in many societies there is ... inheritance of resources, meaning the more elder brothers you have, the fewer resources you will have when you come to reproduce yourself.
And in females, this may be because in many societies there is a wealth transaction when you get married, and younger siblings will have less chance of marriage and less money left over - fewer offspring on average
the number of offspring they produce
Overall, fitness is increased by older ...-... siblings, but reduced by older ...-... siblings. This means there is no ... effect of having siblings on an individual's fitness - siblings are (probably) not ....
opposite-sex, same-sex, net, helpers
Are aunts and uncles helpers?
A similar analysis bu Nitsch et al. (2014) reached the same conclusion (using data from the same population) - no net effect of having aunts or uncles on fitness
A study by Pettay et al. (2016) used data from the same population to plot offspring survival for co-breeding wives against that of non-co-breeders. What was found?
Again, no/non-significant effect.
From this Finnish population, at least, it appears there is little evidence for ... ... in humans, beside the ... effect.
cooperative breeding, grandmother
- this is not necessarily true in all societies (read coursework paper)
As in any other mammal, males have a higher ... ... than females.
The view that humans are monogamous is largely a western idea. If we look across 849 human societies across the world, we find that 0.5% are ..., 16% are ... and 84% are ....
polyandrous, monogamous, polygynous (prevailing mating system)
Polyandry is practiced in small populations across the world, e.g. ... and ....
These are ... communities living at high ... in harsh environments.
Typically there are 2-3 co-husbands per wife (usually ...). 33% of males aged 10-59 were in polyandrous marriages. 31% of females aged 20-59 were unmarried. Unmarried women, on average, have 0.7 children, married women have, on average, 3.3
Why has this polyandrous system arisen in this environment?
Incredibly harsh environment (can reach -40 to -50C, very short growing season, little agricultural land). If land is split up between sons, resources would be very quickly depleted. It appears that polyandry is a strategy designed to avoid overexploitation of the environment.
However, muslim communities in this area of kashmir do not practice polyandry, so culture also influences mating system.
- Environment and culture dictates mating system.
How is conflict within these polyandrous families controlled?
The fact that a woman marries brothers reduces conflict (kinship). At least raising nieces and nephews, even if they don't produce any offspring themselves. There is also an age hierarchy (eldest brother marries usually in early twenties. Youngest brothers likely not of reproductive age yet. Also, often the second brother is sent to the monastery to become a monk.