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Sex Differences in Parental Investment:
Parental Investment Theory states that the sex who makes the larger investment will be
more sexually discriminating, whilst the sex who makes the least investment will be
competing for access to the higher-investment sex.
Investment made by human females is considerably greater than males. This can be
explained by parental certainty, where it is difficult for the male to know if he is the true
parent as fertilisation occurs internally, but human females can be certain if they are the true
Human offspring are born earlier in development therefore, they are relatively immature
compared to other animals. Just like mammals, human female's breastfeed their young, so
they are more burdened with childcare after the birth. Therefore, human females make the
greater prenatal and postnatal contributions.
The costs of childcare are high. The minimum maternal investment would be a nine month
pregnancy followed by years of feeding and carrying. Whereas, the minimum investment for
males would simply be moments of copulation and a spoonful of semen. This is a huge
difference, hence making random mating all the more costly for females.
Due to the high costs of childrearing, females want to ensure good quality offspring so their
efforts do not go to waste. One way to achieve this is to marry a man who has good
resources and is caring. There is some evidence for mistaken paternity (having to be the
father when he is not the biological father),
Women can gain benefit from cuckoldry (when the male raises a child that is not their own
due to an extramarital affair) by receiving additional support from another male and perhaps
high-quality genes for her children. However, there is a possibility of abandonment and the
use of mate-retention strategies (e.g. threats or actual violence against the female/male) by
the current partner.
Because human males make a considerable investment in their children, they have a greater
concern about the fidelity of their mates. So, they try to ensure that their care is not
misdirected towards non-relatives.
Parental Investment Theory predicts that men would invest greater if the child was
biologically theirs. Some studies have contradicted this;
A man whose partner was unfaithful risks in raising a child that is not their own. A woman
whose partner has been unfaithful risks the diversion of resources away from her and the
family as they will be used with someone else. Therefore, sexual jealousy may have evolved
as a solution to the problem, because men become jealous of the sexual act as this results in
cuckoldry, bringing up a child which is not their own, while women become jealous of the
change in emotional focus, because this can result in the loss of resources.
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Males are able to decrease infant and child mortality by providing resources and investing
more on each individual offspring. Hence, males restrict their reproductive opportunities and
It has been suggested that evolutionary perspectives on paternal investment is limited.
Men's parental behaviour depends on various personal and social conditions e.g. relationship
with the mother, personality characteristics of the child and father.…read more