Parental investment

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Parental investment can be defined as ‘any investment by a parent in an offspring that increases the chance that the offspring will survive at the expense of that parent’s ability to invest in any other offspring alive or yet to be born’ (Trivers 1972). Males and females are unequal in their investments of their offspring. 

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The female’s initial investment is a lot greater as the female gamete (egg) occurs a lot less and are more costly to produce compared to the male gamete (sperm). A female can only have a limited number of offspring at one time, which is most commonly one, whereas potentially at one time a male could have thousands of offspring at one time. 

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Because of this biological inequity females therefore must be choosier when it comes to picking a potential mate as they are more favourable to quality of males and their resources, whereas males mainly compete for quantity of females.

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In human female’s maternal investment is a nine-month pregnancy followed by years of feeding and carrying. While the minimum paternal investment would have been a few moments of copulation and a teaspoon of seamen (Symons (1979). This shows there are enormous differences in the potential maximum reproductive success in the sexes, which makes the random mating all the more costly for human females. 

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But there are consequences of greater investments from females which can include extra- marital affairs. As females want to ensure good quality offspring so they don’t ‘waste their efforts’. This could be done by marrying a man who has good resources and is caring but to ‘shop around’ for good genes through extramarital affairs with ‘studs’ who are attractive men advertising good genes but have no resource. 

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Finding data about this topic as finding accurate data for mistaken paternity are notoriously elusive, but there is some evidence of this from a magazine survey of over 2700 UK women. From the results of the survey Baker and Bellis (1990) estimated that as many as 14% of the population were products of extramarital mating’s. 

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But studies like this could have many ethical issues, such as psychological harm to the participants such as stress. The results of these surveys could cause the participants to be distressed by the fact that they could not be their father’s child. This could also cause many family arguments if the ‘father’ didn’t know about the extra-marital affair. 

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This could be prevented by fully debriefing what the survey is about and the results that could be found, and the participants should be allowed to withdraw at any time of the experiment, and all results and names should be kept confidential. 

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But not all males leave as soon as the female gets pregnant, if they stay this can be seen as paternal investment. The minimum obligatory investment for human males is a lot less than the females. 

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Several reasons for this are women can only produce a certain amount of offspring whereas males it could be potentially unlimited. Another factor could be that the females have to carry around the developing embryo for 9 months and care for them many years after the birth, but the males could just walk away if they wanted to. 

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Therefore indiscriminate mating would cost a lot more for females in terms of resources and time, whereas indiscriminate mating in males is a lot less costly (Goetz and Shackelford 2009). But joint parental care is more desirable as there are obvious benefits in the success of the reproduction. Dunbar in 1995 said that in any situation where males can increase the success in childrearing it will pay them to do so.

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. In human males they may restrict their reproductive opportunities and invest more in each individual offspring, as research by Reid (1997) supports the claim that human males do contribute to parenting by providing resources and this investment.  This allows the family to live in healthier environments, resulting in a decrease in infant and child mortality.

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But when males to invest parentally they under the pressure of the possibility of cuckoldry, which is the investing in offspring that are not their own. Because human males make a considerable investment in their children, they have greater concern about the fidelity of their mates (Miller 1998) as it isn’t as obvious that the male is the father of the offspring compared to females as they carry the child and you cannot carry another women’s child naturally. 

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So males try to ensure that their care is not misdirected towards non-relatives. Parental investment theory would predict that investment by fathers would always be greater if they know the child biologically theirs, as they would not want to spend time and resources bringing up another man’s child.

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But some studies contradict this as Anderson (1999) measured the resources invested by fathers and step-fathers for example time spent with the child and financial support given. Men appeared not to discriminate between children born to their current partner from a previous relationship- step children, and their own children from a previous relationship- their biological offspring. 

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This can also be linked to grandparents as the predictions based on paternal uncertainty show differences in maternal and paternal grandparents shown in both historical and modern societies (Michalski and Shackelford 2005). 

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Usually maternal grandmothers invest more in terms of attentive care and protectiveness in their grandchildren, followed by maternal grandfathers, while paternal grandmothers and grandfathers invest the least. 

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Similar differences have been found for aunts and uncles from research by Pashos (2007) so therefore individuals appear to invest more in the maternal line compared to the paternal line. 

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But evolutionary explanations are reductionist, as Rowe (2002) suggests an explanation of paternal investment based on evolutionary factors alone is severely limited. Men’s paternal behaviour depends on various personal and social conditions, which includes the quality of the relationship with the mother, the characteristics of the child and the personality characteristics of the father. 

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But all men are different and it comes down to individual differences. Some men may feel it is necessary to provide resources for a child they never see of isn’t there’s, while others won’t give any resources whether the child is there’s or not. 

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The mother may refrain from telling the male that he is a father in the first place, there are many cases of this and these may not be put into account if you are doing a study that only involves the mother’s answers. This could lead to a loss inn validity and reliability, and the results could not be generalised to other countries or cultures and individual differences is a large part of this research.

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But Belsky (1991) found 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. But correlations lack reliability as they do not show causation only cause and effect and so could hide some of the important factors involved.  

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