Title:
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Tests of Predictions from Kin Selection Theory, Life History Theory and the Evolutionary Psychology of mate choice in Modern Societies
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In this thesis, I demonstrate how sociological data can be used to test predictions derived
from evolutionary psychology, sensu lato. In the first section of the thesis, I test hypotheses
from kin selection theory. Firstly, I test the hypothesis that relatedness influences adult
sibling ties. Using a large scale dataset on family relationships from the Netherlands (NKPS),
I show that both maternal and paternal half-siblings differ significantly from full siblings in
sibling tie strength. In a follow up study, I also show that basic knowledge about a sibling,
namely whether the sibling is still alive or not, varies according to sibling type. If siblings
are not fully related they are less likely to have any basic knowledge about each other.
Subsequently, I test the role of birth order for family relationships and specifically
sibling ties. Kin selection theory suggests, that else being equal, firstborns will invest more
in laterborn siblings, rather than vice versa. Using the same set (NKPS), I show support for
this prediction. Unlike studies from undergraduate populations, however, I fail to find any
evidence for a 'neglected middleborn' effect. Middleborns did not significantly differ from
other birth orders in their sibling ties or their relationships with family members. The
findings on birth order studies are discussed with reference to the current literature on kin
competition, birth order and family dynamics. In the next part of the first section, I analyze
how.childlessness influences family relationships. Kin selection theory suggests that
childless individuals will be more inclined to invest in their siblings with children, than vice
versa. I find support for this prediction in a sample of Belgian women and a sample from an
historical American population. The findings of these studies are discussed with reference to
the helpers-at-the-nest hypothesis.
In the final two studies of this first section I test whether or not lineage affects of
grandparental investment in kin. Using botha Dutch sample and a British sample, I show,
that all else being equal, maternal grandparents, especially, maternal grandmothers, invest
more in their grandchildren than paternal grandparents. The results are discussed with
reference to current research on paternity uncertainty.
In the second section of the thesis, I test predictions derived from the evolutionary
psychology of mate choice, and life history theory. Firstly, I demonstrate the effect of a
biological market on human mate choice using an historical sample. If there is an
oversupply of men on the marriage market then women could demand higher status from
their partner. This prediction from biological market theory was supported. In the following
study, I test the hypothesis that female orgasm frequency is related to male quality using a
sample of Chinese women. I find that male wealth, and to a lesser extent male height,
predict female orgasm frequency. This is consistent with an adaptationist view of the female
orgasm.
In the final part of the second section, I present two studies testing hypotheses
derived from life history. In the first study, I demonstrate that in a stressed environment,
rural Guatemala, 'growing tall' is an accurate predictor of maternal fitness. In the second
study, I evaluate the generalised Trivers-Willard Hypothesis which predicts that taller and
bigger women will have relatively more sons than smaller and thinner women. I fail to find
any support for this hypothesis in British and rural Guatemalan data.
I conclude by briefly discussing why the use of a wide variety of secondary data
resources covering modern societies is important for evolutionary psychology.
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