Extra marital affairs may be a consequence of high maternal investment. The high cost of child rearing to women means that they want to ensure good quality offspring. They may do this by marrying a man that has good resources, so is caring and financially supportive, but then shop around for good genes from good looking men that have no resources. Although this theory is possible there is very little evidence on mistaken paternity to support it. However there is some evidence from a magazine survey of over 2700 UK women. From the results of this survey, Baker and Bellis (1990) estimated that as many as 14% of the population are products of extra marital affairs. However this study may not be credible as it is a magazine survey meaning that it is possible and very likely that the participants may lie or give social desirable answers, meaning that the results of this study lack reliability. Showing that more research needs to be done on the link between maternal investment and extra marital affairs.
Having a child that is a product of an extra marital affair is also referred to as cuckoldry. There are benefits to cuckoldry, however there are also many risks. Benefits of cuckoldry include having a child that have good genes, but also having a partner that is both emotionally and financially supportive of, what they believe to be, their child. One disadvantage of cuckoldry is the possibility of abandonment if the women's partner was to find out. Daly and Wilson (1988) also said that there is a high risk of violence by the current partner towards the woman and the other male.
Commonly parental investment is significantly less than maternal investment. It is suggested that this is due to the act that males have to protect themselves from the risk of cuckoldry, investing in a child that isn't theirs. As a result of this they try to ensure that they do not misplace their investments into non-relative through things such as adultery laws. Sexual infidelity proposes different adaptive problems for males and females. A male whose partner was unfaithful risked investing in a child that is not their own. Whereas a women whose partner is unfaithful risks diversion of resources away from herself and her family. Buss (1995) suggested that sexual jealousy may have evolved as a solution to these problems. Men are more jealous of sexual acts, whereas women are more jealous of the shift in emotional focus.
Consistent with predictions based on paternal uncertainty, differences in investment made between maternal and paternal grandparents have been found in both historical and modern societies. Michalski and Shackelford (2005) found that typically, as the parental investment theory would expect, the maternal grandmother invested most (most attentive and protected) followed by maternal grandfathers, then paternal grandmothers and lastly paternal grandfathers. Similar differences have been found in other family members such as aunties and uncles. This shows that in general individuals from the maternal line tend to invest more that family members from the paternal line.
Evolutionary explanations do provide a logical explanation of paternal investment, however some people argue that they are reductionist. For example Rowe (2002) suggests that an explanation of paternal investment based on evolutionary factors alone is severely limited. The way and extent to which a man invests in his child may be down to a number of factors such as personal and social conditions, such as the quality of the relationship that they have with their partner, and the characteristics of the child and the male himself. Belsky (1991) claims that childhood experiences such as parental divorce tend to correlate with the degree to which man invest in their own children. This shows that evolutionary explanations of paternal investment are reductionist as they do not consider the number of different factors that may affect paternal investment. It also shows that overall the explanation on paternal investment is deterministic as it assumes that all men typically invest very little in their children because they are male and ignores the possibility that in some cases a father may be more investing in a child than their mother.
Parental certainty is used to explain paternal investment. However research has indicated that parental certainty is not always an issue for human males. Parental investment theory suggest that investment by fathers would always be greater if they knew that they child was biologically theirs. However some studies have contradicted this suggestion. Anderson (1999) measured the resources (time spent with child and financial support) invested by fathers and stepfathers. From his study he found that there was little difference in the investment men made in their step children and their own biological children. This shows that the parental investment explanation of paternal investment may not be credible as its main explanation, parental certainty, may not be a determining factor to the paternal investment made by males.
