Parental investment theory was introduced by Robert Trivers in 1972. In this theory, Trivers linked the levels of parental investment in their offspring with the potential of this offspring’s survival in the future, as well as the parental ability to invest in a new offspring once the current one is grown. In that way, parental investment was viewed as a direct connection with the processes of natural selection mentioned by Darwin (Trivers 52-53). Parental investment may differ in its degree between the representatives of sexes. To be more precise, in most cases, one of the sexes has a more obligatory investment in offspring than the other. The sex with a higher level of obligatory investment tends to treat the processes of mating and sex with more caution and carefulness, thoroughly picking potential partners. At the same time, the sex with a lower level of obligatory investment in offspring typically displays more aggressive sexual behaviors and is less selective in terms of choosing a potential partner.
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In particular, among mammals, females are the higher-investing sex in terms of parenting. In that way, as it was mentioned previously, the major implication from this tendency is a more selective attitude towards the choice of a mating partner among women. At the same time, men are the lesser-investing sex, and, as a result, they stereotypically are more sexually aggressive and are less choosy in regard to picking partners for short term relations.
In addition, Bjorklund and Shackelford noted that due to the differences in the degrees of obligatory parental investment, men and women have different attitudes to their partners’ infidelity (87). To be more precise, men display stronger emotional reactions to the idea that their female partners could be having casual sex with other men rather than the idea that the women developing a strong emotional connection with other men. However, the perspective of women on the same two ideas is the opposite. Women experience a stronger emotional reaction to the idea that their long-term male partners could develop a strong emotional connection with another woman.
This happens because, for women, the consequences of emotional infidelity of their partners usually meant the loss of resources that they provide (Bjorklund and Shackelford 87). Moreover, Kokko and Jennions noted that under the circumstances of men and women having different purposes in terms of parenthood, the low-degree investment of males is supported by one very significant factor (922-923). To be more precise, as males have to compete for their partners with the objective of becoming able to mate with as many as possible females, it would not be reasonable for them to invest in the parenting of a single offspring since this reduces their chances of finding another mate and having another offspring.
Moreover, Mascaro et al. explored the nature of the behavioral dimorphism in relation to the levels of parental investment in males and females and found that under various conditions, the investment of females remains to be higher than that of males (2-4). However, reevaluating the logic of the standard approach to parental investment ratios among males and females, Wade and Shuster noted that the evolution of male parental care takes place independently of the female level of investment and is directly connected to the viability rates of the offspring depending- on the paternal parental care (287-289). In other words, males and females begin forming pairs in order to care for the offspring together when the viability of the offspring increased by the paternal investment becomes higher than that occurring when males pursue having more offspring with different mates. It is possible to consider this tendency to be one of the factors that contributed to the change in the levels of parental care provided by contemporary humans compared to the dynamics that used to be in place thousands of years ago.
Additionally, the levels of parental investment are strongly determined by the life history of the participating males and females (Coleman and Gross 404-406). To be more specific, the individuals’ past and future plans, threats, and benefits influence their decisions as to engaging in more mating behaviors for the purpose of producing offspring. For example, one of the most significant factors that could impact one’s readiness to have offspring is the size of the existing brood. This is particularly relevant for individuals whose parental investment is of a lengthy nature. For instance, human children tend to mature much slower than those of most other mammal species. As a result, having several children to take care of, a man or a woman is likely to become less willing to have more offspring.
To sum up, the parental investment theory explains multiple sex-related differences between men and women. Specifically, these differences revolve around such concepts as eagerness and cautiousness in regard to mating, as well as polygamy and sexual promiscuity. The differences in parental investment levels contribute to a variety of cognitive and behavioral implications for men and women, such as the difference in perceptions of infidelity, varying readiness to mate and have offspring, and dissimilar criteria and strategies for the choice of partners.
Bjorklund, David F. and Todd K. Shackelford. “Differences in Parental Investment Contribute to Important Differences between Men and Women.” Current Directions in Psychological Science, vol. 8, no. 3, 1999, pp. 86-89.
Coleman, Ronald M. and Mart R. Gross. “Parental Investment Theory: The Role Of Past Investment.” Trends in Ecology & Evolution, vol. 6, no. 12, 1991, pp. 404-406.
Kokko, Hanna and Michael D. Jennions. “Parental Investment, Sexual Selection and Sex Ratios.” Journal of Evolutionary Biology, vol. 21, 2008, pp. 919-948.
Mascaro, Steven, et al. “ALife Investigation of Parental Investment in Reproductive Strategies.” Artificial Life VIII, edited by Russell Standish, Mark A. Bedau and Hussein A. Abbass, MIT Press, 2002, pp. 358–361.
Trivers, Robert L. “Parental Investment and Sexual Selection.” Robert Trivers, n.d., Web.
Wade, Michael J. and Steven M. Shuster. “The Evolution of Parental Care in the Context of Sexual Selection: A Critical Reassessment of Parental Investment Theory.” The American naturalist, vol. 160, no. 3, 2002, pp. 285-292.