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Transcript of Parental Investment
Parental Investment (PI)
Theory states that PI is any investment by a parent to an individual offspring.
To be worthwhile it is also supposed to enhance the chance of survival of the offspring even though it may be at the cost of other offspring.
Men can opt out of investing in their child whereas females have prenatal and postnatal responsibilities. Males can afford to devote little in comparison to females
(Daly and Wilson, 1978)
Males have potentially unlimited gametes (sperm), however women only have a certain number of gametes (eggs). Women therefore have to be more
in their choice of partner as they need the
in a partner. Men compete for the
The minimum investment for males is much less than females.
Females have to carry and protect the developing baby for 9 months before it is even born. Then they have to wean the child for years after, whereas males can walk away after achieving fertilisation.
mating is much less costly to men.
(Goetz and Shackleford, 2009)
When males do invest their resources, they are at risk of
(raising a child which isn't their own), which then means they have wasted their resources.
Men are more jealous of
because if their mate is unfaithful they risk cuckoldry, whereas women are more jealous of
because if there mate is unfaithful they run the risk of losing valuable resources.
Sexual jealousy may therefore have evolved from this problem
Increased brain size through
by our ancestors, results in difficult childbirth. Meaning that children are born prematurely compared to other animals and mothers have to invest more time and care into the infants over a longer period.
Therefore human mothers have greater
prenatal and postnatal contributions.
A benefit of maternal investment is that the mothers have
that the child is theirs.
Maternal investment is far greater than paternal investment.
Baker and Bellis (1990)
estimated that 14% of the population were a product of an extra-martial affair.
For women extra-marital affairs can mean that they have good quality offspring: marrying a man with good resources and get the good genes from affairs with 'studs'
The are also risks associated with
such as abandonment and the use of male-retention strategies by the current partner.
Maternal investment can be linked in with
due to parental certainty, because unlike males females can be certain that they are the parent of the offspring this therefore means that they are carrying on their genes.
On the other hand this evolutionary explanation doesn't explain why cuckoldry occurs.
Maternal and Paternal grandparents also differ in investment towards grandchildren. Maternal grandmothers invest the most, followed by maternal grandads. Paternal grandparents invest the least. This backs up the theory that women have a far greater investment in their offspring.
Males do Invest
Despite them being able to easily walk away, men do stay and in humans they restrict their reproductive opportunities and invest in their own children.
supports the claim that human males invest by
, meeting the woman's
Parental Certainty isn't always a problem
For some men it would seem that cuckoldry isn't a problem.
compared resources invested to children, with biological
fathers and step-fathers.
He found that there was no difference between either. There was no discrimination between their children and their step-children.
Are Males Biologically less prepared?
Geher et al. (2007)
studied 91 non-parent undergraduates to see whether males are biologically less prepared than females to invest. They found
no differences in self-report responses
males showed clear ANS arousal
when faced with different parenting scenarios. Researchers concluded that males are less prepared, which is consistent with the predictions from PI theory.
Research comparing human PI to chimpanzee PI has suggested that male parenting is either a
dramatic evolutionary change
or a contribution of
suggests that evolutionary explanations of paternal investment are reductionist
as there are various other contributing factors to