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Parental Investment in Mammals

Mammals are another large group that emerges with regard to parental care strategies, and obviously the group that Humans fall into.  The vast majority of mammals display female-only parental care, with roughly ten percent providing bi-parental care, and no instances of male-only care (Gross 2005).  For mammals, female parental investment is initially greater than male parental investment.  Females produce a relatively large egg which is in and of itself a greater investment than the small male sperm.  Additionally, if that egg is fertilized, the absolute minimum investment of a female is the term of her pregnancy-which is by no means a small investment.  This investment is much greater than the initial male investment, which at a minimum is his sperm (Trivers 1972).  For example, the only investment male orangutans-primates like ourselves-provide is sperm (Diamond 1992).  While it is true that the majority of mammals follow this pattern where males invest only their sperm and females invest in an egg, pregnancy and child rearing, humans fall into the minority of mammals which share parental investment between the two sexes (Gross 2005, Woodward and Richards 2005).

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