Parental investment

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Outline and evaluate the evolutionary explanation of Parental
Investment (24 Marks):
Trivers defines parental investment as any investment made by the parent in an
individual offspring that increases the offspring's chance of surviving at the cost of
the parent's ability to invest in other offspring.
Female investment tends to be far greater because female gametes (eggs) are
limited and more costly to produce than male gametes (sperm). They also invest
more because they carry the baby for 9 months and breastfeed the baby after it's
born. Also, a mother can always be positive that the baby is hers whilst a father can
never be too sure thus they invest less. The great vulnerability for men is that they
invest too many resources in a child that may not be there's. For a man, an unfaithful
mate meant that he risked investing in offspring that were not his own. This is known
as cuckoldry. For women, an unfaithful mate may have led to the diversion of
resources away from her and her family. Buss suggested that sexual jealousy might
have evolved as a solution to these problems. Men may be more jealous of their
mate engaging in sexual contact with other males whilst women are more jealous in
the shift of emotional focus. Women are also generally choosier in the selection of
partners because they have more to lose from the negative match. A female's best
strategy is to select a resourceful, fit male to increase the survival of offspring. As a
result, it will lead the offspring to spread their genes so that they are passed on to
the next generation.
Buss (1995) suggested that sexual jealousy is higher in males than females. This is
related to the fact that for males it is a priority to have faithful women in order to
avoid investing in offspring that isn't theirs. His study in 1992 supports this as males
showed a higher galvanic skin response when asked to imagine sexual infidelity by
their partner, than females. However, Harris found that males have greater arousal
from any sexual imagery whether it's relevant to them or not. She suggests that sex
differences in jealousy are more likely to be a product from social learning than
evolutionary hard wiring. Daly and Wilson explain that males devote most of their
time and effort in courtship to ensure high levels of reproduction; this can explain
why less time remains for investment. However, a limitation of this study is that
results have been found using animals and may not be generalizable to humans as
we are different mechanism thus act differently. Therefore this decreases the
reliability of the evolutionary explanation for parental investment.
However, in reality fathers do invest in their children and do help out. Increasing
brain size over the years has led babies to be born prematurely thus more
investment by both parents is needed in order for the offspring to survive. According
to the parental investment theory, males are more likely to care for their biological
children than non-biological. However, Anderson et al (1999) suggest that this is an
oversimplification as he found that males treated their step-children and biological
children who were living with them similarly. This in itself can be explained by the
evolutionary theory as males care for their step-children in order to gain greater
access to their mother.

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To verify if the lack of commitment was due to nature or nurture, Geher asked 91
students from New York University to complete a parental investment perception
scale to measure how they see themselves as parents in the future. There were no
difference between males and females. This suggests that men and women are
socialised to invest in their offspring. However, when asked a question on actual
parental investment level (e.g.…read more


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