This is made more difficult in more promiscuous mating arrangements where there is a risk of cuckoldry, as they cannot be certain of the fidelity they try to ensure that care is not misdirected towards non relatives. A man whose mate is unfaithful risks offspring not his own, a woman whose mate was unfaithful risks a diversion of resources.
Buss suggested that sexual jealousy may have evolved as a solution to this problem. Men are more jealous of the sexual act itself, while women are jealous of the shift in emotional focus and the loss of resources and investment into another woman.
There are 2 consequences of the high cost of maternal investment. It would mean that females want male providers but also want good quality children. A way to achieve this would be to marry a man with good resources and caring, but ‘shop around’ for men with good genes through extra marital affairs. Baker found results from a magazine survey with 2700 UK women that 14% of the population could be due to extramarital affairs, supporting this theory that women want the best genes for their children, whilst being able to have a man provide financial support. However the small sample size means it’s difficult to generalise the data to a much larger uk population. Also the sample suffers from cultural bias, with it only focused on UK women, meaning results may be ethnocentric and not generalisable across other populations. Along with this the results being from particular types of magazines may attract a certain demographic, including people which may engage in behaviours, causing a biased result, therefore it is hard to establish cause and effect from such survey results.
The theory can be supported by Buss, who shows a link between the Parental investment theory and sexual jealousy. He found that male US students indicated more concern over sexual infidelity, but women were more concerned about emotional infidelity. This supports the theory as it suggests that females care more about an emotional investment, but men care about the sexual investment.
The theory can be criticised by Anderson who measured resources given by dads and stepdads and found that men didn’t discriminate between their own children and children from other relationships. This criticises the PIT as that would say that paternal investment would be greater if the child was biologically his, as males don’t want to spend resources on another man’s child, but this research suggests that men will invest equally in children that are not their own.
Another criticism of the theory is that it’s reductionist. Rowe suggests that parental investment can’t be down to evolutionary factors alone, and that men’s parental behaviour depends on personal and social conditions, including the quality of the relationship with the mother, and characteristics of the child. The theory is also deterministic as it does not factor in people’s ability for conscious thought and free will. Many females care for children that re not her own in relationships, as do men. Couples even adopt, putting equal amounts of energy in, despite there being no biological link, proving our ability to break away from our genetic programming.
Dunbar criticises PIT as he suggests that males restrict their reproductive opportunities and invest more in individual offspring as this is more desirable due to the high costs of successful reproduction. This critics the theory as it shows that men have a choice and are not interested in unlimited offspring like the theory suggests.
The parental investment theory also suffers from a gender bias, as it portrays men to be more susceptible to cheating and infidelity, but in truth this is not the case and there are cases of both genders behaving this way as a man cannot mate without a willing female either.
Gross and Shine support the theory as they found with internal fertilisation, care is carried out by 86% of females while external fertilisation has 70% paternal care by males, supporting the idea that parental certainty plays a huge factor in the parental investment made by each gender.
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