This theory argues that differences in male and female reproductive behaviour are due to the amount of parental investments made by both sexes. Human males’ parental investment is relatively small compared to human females. A man has an indefinite amount of sperm and will remain fertile all his life. Therefore, they won’t have a problem producing as many children as they would like to because it doesn’t take that much time or energy to have sex. The best way for a man to maximise his reproductive success is to mate with as many women as possible. Due to their unlimited amount of sperm, men tend to go for quantity rather than quality and hence, will have a higher number of sexual partners throughout their lifetime than women do.
Women on the other hand have a very large parental investment. Women have a limited amount of eggs once they are born. Once they start their menstrual cycle they lose one every month. So in essence if we look at the number of years they have to have children, it will be around 30 years. Therefore there is a limited amount of offspring they can have as they only ovulate once a month. Following conception they have to carry the baby for 40 weeks. After they go through childbirth to deliver the baby, they have to take care of their children who are much more premature than offspring of other species, due to evolution of skull size. Due to this women will take longer in rearing their children as they will have to breastfeed. Not only will this affect her figure, but more importantly their health. Due to all these factors, women will go for quality rather than quantity as this will ensure a better father for their children.
Firstly, we can conclude that this theory offers a plausible explanation as to why there are differences towards reproduction in genders. In conjunction with the theory, Buss and Scmitt 1993 proposed the predictions that women seek good genes and go for men with money due to their high PI. As women invest so much, they want their offspring to have as many resources as possible and good genes will provide a good immune system. Men on the other hand have a low PI so try to go for as many women as possible, as well as trying to go for young women as this shows signs of fertility and health.
Alongside to this, it helps us understand differences in jealousy. It allows us to comprehend why men are more concerned about sexual infidelity whereas women are more concerned about emotional infidelity. If a man’s partner sleeps with someone else they raise the risk of raising someone else’s child. This is devastating for them as they are wasting their resources for someone that doesn’t even share their genes. Women don’t have this problem as they know it’s their child. However, if a man falls in love with someone else, then the resources will be shared amongst them. This will cause major repercussions for the women as they won’t receive all the attention they did before, the money will be shared so their lifestyle will have to change and the child will also get less attention from the father.
However, the theory is reductionist because you’re putting something as complex as why there are differences in reproductive behaviour and deconstructing it into genes and characteristics. We’re ignoring other factors that influence our mating behaviour for example our upbringing. This could influence this behaviour as those who have been brought up in a very religious family will only believe in sex after marriage and only for creation. Therefore these individuals won’t engage in one night stands or anything along those lines. There are other factors like biology, social background and past experiences, for example those who have been raped or sexually abused will have a different reproductive behaviour to those that haven’t for obvious reasons.
It doesn’t account for individual differences because not all mating behaviour is about long term relationships which results in children. There are some individuals that have sex for pleasure but will never have children as they are focused on their careers or other aspects of their life. There is evidence that there are an increasing number of women having one night stands and short term relationships. Pérusse 1993 suggest that this increasing number, especially in western societies, is due to contraception. In wealthier countries, males and females have sex more frequently, but not for procreation and socially enforced monogamy, just for pleasure. Furthermore, Sternglanz and Nash in 1999 found that one night stands don’t tend to result in pregnancy which could in turn cause more women to be willing to have sex with random men.
Moreover it is deterministic as they assume our behaviours are determined by our genes. There is free will which overpowers the genes and allows us to make our own decisions. Human behaviour isn’t animal behaviour. Ours is controlled more by conscious, cognitive factors so we may suppose that interpersonal attraction will be less governed by evolutionary pressures than it is in animals. There is free will because you can choose when you want to have sex and with who you want to have it with. This has nothing to do with evolution.
In humans, joint parental investment is much more desirable because of the high cost of successful reproduction. This means that males restrict their reproductive opportunities and invest more in each individual offspring. This results in greater male selectivity. This explains why female physical attractiveness (which indicates fertility, health and good genes) is so important compared with the lack of choosiness of other animals.
Culture also has a big role in shaping reproductive behaviour. For example, it is socially acceptable for men to be promiscuous. Those men who sleep with many women will be seen as a ‘legend’, or a role model for other men, because it’s every man’s dream to sleep with a large number of women. However, if women are promiscuous and sleep with more than a handful of people they will be shunned upon. If we look at female chimpanzees, they are very promiscuous, so males have to compete a lot. They have evolved to have large testicles to provide sufficient sperm. Gorillas on the other hand have small testicles compared to their body size because females are monogamous so there is little competition. Human males have medium sized testicles by primate standards. Baker and Bellis (1995) suggested that the norm for ancestral males was to compete, so females must have been promiscuous and had various partners. Therefore, due to these findings it wasn’t frown upon for women to be promiscuous as it is nowadays.
Lastly, we have to take into consideration the Sexual Strategies Theory which was proposed by Buss and Scmitt in 1993. They suggested that people will use long term and short term relationships whenever it suits them. This means that the range of possible reproductive behaviours is large and isn’t just limited as to how much parental investment individuals put in. Although it acknowledges that certain characteristic are desirable because they have evolutionary advantages, it also explains that we do have a choice in how we behave and what we choose to do, i.e. free will.
To conclude, we can gather that the theory does explain differences in reproductive behaviour of genders rather well, as it offers a plausible explanation. However there are various criticisms of the theory. Nonetheless, it is a theory and not a hypothesis so there is enough evidence that supports the claims of the PIT.
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