Self-Domestication in Pan paniscus : Evolution of Hominin Sexual Behavior

1. Abstract • Does the amount of time a male spends participating in nonconceptive sexual behavior, as a prosocial behavior to males and females, increase a male’s reproductive fitness as a potential conceptive mate? • Male bonobos utilize NCS as a prosocial signal in order to form bonds through the display of an honest signal. • An increased proportion of time spent on nonconceptive sexual behavior will account for an increase in a male’s hierarchal rank in proportion to other male’s within the bonobo, Pan paniscuspopulation. • Research Question & Hypothesis • Introduction • Subjects & Methods • . • Predicted Results: • In the event that our results are confirmatory, we will be able to conclude that among bonobos, males utilize NCS as a prosocial signal in order to gain hierarchical rank, following the Costly-Signaling Exchange Theory. In the event that our results are non-confirmatory, wherein males with lower rank show increased N.C.S. behavior, such results suggest that inferior males are using NCS as an adaptive strategy to acquiremorereproductive opportunities from superior males. In the event that our results are not significant, future research should be conducted to find an alternative explanation for NCS activity in bonobos. • Discussion: • The results from this research will provide many implications for primate and hominin sexual behavior. If the results are confirmatory this will provide continued research as to the effects of self-domestication. This research will allow for increased understanding of how socioecological pressures can shape sexual behavior among primates and humans.Humans exhibit the most NCS behavior of any primate, It would be faulty to assume that such behavior does not serve evolutionary function. This research suggests that increased NCS behavior is indicative of convergent evolution with bonobos. The mechanism behind this specificconverging evolution could be explained through self-domestication. For instance in modern Westernized society, many analogous socioecological traits exist to include; reduced aggression, increased equality in relationships, mate-choice exhibited by both sexes, and reduced food competition given a surplus in resources due to agriculture. Human females like primate females favor NCS which stimulates the clitoris (Waal,2006). The potential confirmatory results imply that NCS behaviors are significantly influenced by these socioecological factors making NCS behaviors a prosocial signal. Uponreview, anadditional implication taken from the confirmatory results, discussesthe proximate function of the clitoris as it relates to the mate choice hypothesis (Puts et al., 2012, Hrdy, S. B. 1995). Extensiveresearch may corroborate shown results and serve toexplain how relationship satisfaction in modern Western human populations is influenced. Research by (Ellsworth, 2013) indicates that relationship satisfaction has been correlated with frequency of orgasm in females. See figure 1 below. • Predicted Non-Confirmatory Results • References • Predicted Confirmatory Results • Predicted Results & Discussion • Self-Domestication in Pan paniscus : Evolution of Hominin Sexual Behavior • Mark Cunningham, Ashley Henard, & David Samson • University of Nevada, Las Vegas • Research Question: • Hypotheses: • Experiments suggest that self-domestication can have multiple effects upon the behavior, morphology, psychology, and physiology of the bonobo, Pan paniscus. The purpose of our proposed study is to examine whether or not a male’s nonconceptive sexual (NCS) behavior is prosocial towards female and/or male bonobos and if this behavior is positively correlated with a male’s hierarchal rank and reproductive fitness. We hypothesize that 1) bonobo male’s nonconceptive sex acts as a prosocial signal toward females and/or other males, and 2) that higher ranking bonobo males will engage in more nonconceptive sex than lower ranking males. We detail the role of nonconceptive sex in relation to female orgasm. We show that females evaluate male signals in order to perceive a willingness to invest. We intend to use observational focal follows within a longitudinal study. We propose that male bonobos have evolved to utilize nonconceptive sexual behavior as a strategy to increase their reproductive fitness. The results will aid in research to provide parallels for understanding how human and bonobo sexual behavior can be selected by nature as a reproductive fitness strategy dependent upon a changing socioecological nature. • Model of Bonobo Self-Domestication (Hare & Wrangham, 2012) • Research shows that bonobo NCS acts include behaviors such as oral sex, genito-genital rubbing, masturbation, and penis fencing (Manson, 1997). Research goes on to show that bonobos and other primates exhibit pleasure-responses strongly indicative of orgasm ( Wall, 2006). In order for primates to utilize NCS as a prosocial utility it must provide the receiver with a physiological benefits. • Costly-Signaling Exchange Theory (Wrangham, 1993) • Subjects: • 24 bonobos categorized into three groups: 1) Dominant (n=8), 2) Sub-dominant (n=8), 3) Inferior (n=8). • Hierarchal social rank will be assessed based on dyadic interactions. • All subjects will be 7 years of age (reproductive age) or older. • Methods: • A systematic behavioral observation will be conducted of focal bonobos in the region of Salong National Park in the Democratic Republic of Congo for a period of one year. • Ethnogram coding language will be used to record observational data. • Using an ANOVA, Analysis of Variance will test for significant differences between the means of the dominant and inferior groups. • 1) Male bonobos perform NCS • 2) NCS incurs a “cost” because it is not directly beneficial to the male, making the act an inherent vulnerability • 3) NCS becomes an honest signal depicting the male’s degree of altruistic behavior • 4) Such costly sexual acts communicate male’s willingness to invest • 5) These acts also demonstrate a partner’s willingness to accept vulnerability Non-confirmatory Non-significance • De Waal, F. B. (2006). Our inner ape: A leading primatologist explains why we are who we are. Penguin. • Hare, B., Wobber, V., & Wrangham, R. (2012). The self-domestication hypothesis: evolution of bonobo psychology is due to selection against aggression. Animal Behavior, 83(3), 573-585. • Hrdy, S. B. (1995). The primate origins of female sexuality, and their implications for the role of nonconceptive sex in the reproductive strategies of women. Human evolution, 10(2), 131-144. • Manson, J.H., Perry,S., & Parish, A. R. (1997). Nonconceptive sexual behavior in bonobos and capuchins. International Journal of Primatology, 18(5), 767-786. • Puts, D., & Dawood, K. (2012). Why Women Have Orgasms: An Evolutionary Analysis. Archives of Sexual Behavior, 41(5),1127-1143. • Wrangham, R. W. (1993). The evolution of sexuality in chimpanzees and bonobos. Human Nature, 4(1),47-79. Social Rank Social Rank