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Ayisha J

on 27 April 2014

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Parental investment is described as any investment by a parent in any offspring that increases the chance that the offspring will survive and pass on their genes, (Trivers 1972). At the heart of Trivers theory is the fact that in most species males and females do not invest equally, females initial investment is far greater than the males (eggs) which is more costly than (sperm). Males can have as many children as they want, however the amount of children a women can have is limited. Therefore women are more choosier than men.
Sex differences in parental investment; the most obvious sex difference in human parental investment is that males can opt out of parental investment when they wanted but women cannot (Daly and Wilson 1978). This theory states that the sex that makes the larger investment will be more sexually discriminating whereas the sex that makes a smaller investment will compete for access to the higher investing sex. In humans the more discriminating sex would be females.
Maternal investment; investment made by females is greater than males due to limited eggs and unlimited sperm. Another reason may be paternal certainty, females are certain about who the true parent of their child is.
Why do human females invest more?
Brain size has increased in response to adaptive pressures, this resulted in a more difficult childbirth due to enlargement of the skull. To compensate for this childbirth in humans occurs earlier in development, meaning that human infants are born immature. Females breastfeed their child and so are more burdened by the extended period of childcare. Hence human females not only make a greater prenatal contribution of resources but also make a larger postnatal contribution.
The cost of maternal investment; for females this includes a nine month pregnancy followed by years of feeding and carrying. Whereas for males it is just providing the sperm (Symons 1979). The result is an enormous difference in the potential maximum reproductive success of the sexes, so random mating for females is more costly.
Paternal investment; the minimum obligatory investment made by human males is considerably less than females (egg vs sperm). Another reason is that whilst females have to carry the embryo for 9 months and then care for the child for many years while the male can just walk away after having achieved fertilization. Therefore indiscriminate mating has more costs in terms of time and resources for a woman compared to a man (Goetz and Shackelford 2009).
Sex Differences in Paternal Investment
Paternal Investment and cuckoldry; when males do invest parentally through their resources, they are under pressure to protect themselves from cuckoldry (investing in an offspring that is not theirs). Due to this investment males have a greater concern than females about the fidelity of their partners ( Miller 1998).
Sexual and emotional jealousy; the possibility of sexual fidelity causes different adaptive problems for males and females. A man is at risk of investing in an offspring that is not his, a woman whose mate was unfaithful risked the diversion of resources away from her and her family. Sexual jealousy may have evolved as a solution to these problems (Buss 1995). Men are more jealous of sexual acts whereas women are more jealous of shift in emotional focus.
Maternal (invest more) vs Paternal
Grandparents (Michalski and Shackelford 2005).
Uncles and Aunt's ( Pashos 2007).
Research Evidence; are males less prepared than females to invest?
Geher et al (2007) studied 91 non-parent undergraduates, each completed a parental investment perception scale, which included statements such as 'I am ready to be a parent at this time in my life'. They were also exposed to various parenting related scenarios such as 'your daughter has an ear infection, your plans for the whole day have changed'. There were no sex differences in self-report responses to parenting on the parental investment perception scale, there were clear differences in ANS arousal to different parenting scenarios. Researchers concluded that as per the parental investment theory males are biologically less prepared than females to confront issues linked to parenting.
The consequences of greater investment by females...
Extra-martial affairs; women want to ensure good quality offspring to ensure that they aren't wasting their time. Therefore they marry a man who has good resources and is caring, but shop around for good genes through extra marital affairs. Baker and Bellis (1990) from a magazine survey of over 2700 UK women found that 14% of the population were products of extra martial affairs.
The benefits and risks of cuckoldry; some women attempt to offset their greater parental investment by cuckolding their partners, this way they get additional social support from their partner and an offspring with good genes. However for a woman doing this is not without risks, such as the possibility of abandonment and mate-retention strategies by the current partner (Daly and Wilson 1988).
Commentary on paternal investment...
Males do invest; joint parental care is desirable because of the benefits of successful reproduction. In any situation where males can increase the success of child rearing it will pay them to do so (Dunbar 1995). In humans males may constrict their reproductive opportunities investing in each individual offspring. Research by Reid (1997) supports the claim that males do contribute to parenting by providing resources and this investment allows the family to live in a healthier environment.
Paternal certainty is not always an issue for human males; parental investment theory would predict that investment by fathers would always be greater if they know the child is biologically theirs. They wouldn't want to spend time and resources rearing another man's child. However some studies have contradicted this assumption, Anderson (1999) measured the resources invested by father's and step fathers, men appeared to not discriminate between children born to their current partner from a previous relationship and their own children from a previous relationship.
Evidence for sex differences in jealousy; in line with the PI theory predictions about sex differences in type of jealousy (Buss et al 1992) found that male US students indicated more concern about sexual infidelity whereas female students expressed more concern about emotional infidelity. This was supported by physiological responses when respondents were asked to imagine scenes of sexual or emotional infidelity. However Harris (2003) found that men tended to respond with greater arousal to any sexual imagery which challenges the view that sex differences in jealousy are an adaptive response in males and females.
IDA- Evolutionary explanations are reductionist; Rowe (2002) suggests that an explanation of paternal investment based on evolutionary factors alone is severely limited. Men's parental behavior depends on various personal and social conditions, including the quality of relationship with the mother, and personality characteristics of the father. Belsky (1991) 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 child.
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