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Sex differences in parental investment - 1

Parental investment theory states that the sex that makes the larger investment will be more sexually discriminating, of the two sexes, it is females that are choosier. Bateman argues that this is due to the difference in production of gametes. A female is born with all of the eggs that she will ever produce in her lifetime. Where males produce many small gametes.

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Sex differences in parental investment - 2

Trivors developed Batemans principle further and suggested that the entire investment made by a parent including gestation, protection and feeding are taken into account and not just their gametes. They suggest that the sex who invests the most in the offspring can afford to be the choosiest, as they have the greatest burden. The ‘cost’ of an egg doesn’t stop after production, the women has devote a lot of time after birth ensuring the protection etc. of the child, human babies are born with a much lower maturity than most animals due to the skull size which means that they are unable to physically survive without care. Females must make a larger investment to ensure existence. In addition to this, women’s fertility declines rapidly after thirty years meaning that a women can only have an average of 12 children whilst a man can mate freely for the majority of his life. This is why women are the choosier sex. 

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Sex differences in parental investment - 3

Hatfield conducted on 96 university students, he wanted to find out which sex is the choosiest. The question that was asked was ‘I have seen you around and I find you very attractive will you…. A) go out with me B) come back to my apartment or C) come back to bed with me. He found that 75% of male students agreed to get straight into bed with someone where 0% of women agreed to sex. This supports parental investment theory, with the idea that women are the choosier sex.

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Sex differences in parental investment - 4

Further support comes from a study that Buss conducted on males and females, he asked them on average how many partners on average they would want to mate with. On average men said 17 as opposed to women who on average said 4.5. This supports parental investment theory that suggests that males want to be mate with more women in order to pass on as many of their genes and that women are choosier as they don’t want to waste their limited amount of eggs.

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Sex differences in parental investment - 5

Research that refutes the idea of low male investment comes from Dunbar who argued that joint parental care is desirable because this produces successful reproduction. In any situation where males can increase the success of childrearing, it will pay them to do so. In humans, males may restrict their reproductive opportunities and invest more in each individual offspring. Research from Reid supports the claim that human males do contribute to parenting by providing resources such as food, this investment allows the family to live in healthier environments, resulting in a decrease in infant and child mortality

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Sex differences in parental investment - 6

However Rowe suggests that an explanation of paternal investment based on evolutionary factors alone is severely limited. Evolutionary explanations are reductionist. Men’s parental behaviour depends on various personal and social conditions, including the quality of the relationship with the mother the characteristics of the child and the personality characteristics of the father. Belsky also claims that childhood experiences such as parental divorce tend to correlate with the degree to which men invest in the upbringing and care of their own children. 

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