Primate Sexuality: A Comparative Study

Chapter 1: introduction

1.1 Background of the study

Primates have been linked as species sharing the same evolution pattern with human beings. In fact, studies on evolution point to the fact that human beings evolved in the same family with the great apes which include Bonobos (Pan paniscus) and Orangutans (Pongo pygmaeus and Pongo abelii). Dixon (2012) explains that natural and sexual selection resulted in the differences among human beings and other primates. However, the fact that human beings share the same tree of life with these primates signifies that certain key aspects (such as sexual behavior) are quite similar. This led to increased studies to explore the sexuality and sexual behavior among the primates. In one of the studies, George Simpson (1945) divided the order primates into two main groups depending on their body morphology and behavior (sexual included). These sub-orders are the Prosimii (lemurs, lorises, galagos, and tarsiers) and Anthropoidea (monkeys, apes, and humans). From this classification, there are key differences especially in regards to sexual behaviors between members of each suborder. For instance, George explains that generally, prosimians are nocturnal (with some diurnal lemurs) and adults occupy individual overlapping home ranges. Olfactory communication is extensively used in both sexual and non-sexual contexts and females have relatively brief periods of sexual receptivity or “estrus” coinciding with the timing of ovulation. Among the anthropods, there are some variations in the sexual behaviors among members of the group. For instance, New World monkeys are arboreal and make use of urine and cutaneous secretions in social and sexual communications. The Old World monkeys rely more on visual cues than secretions in sexual communication. For instance, female adults develop large pinkish or reddish skin swellings during their follicular phase of the ovarian cycle. This is also common among some apes such as Bonobos (Birkhead et al., 1987; Hrdy, 1988; Wrangham, 1993).

Research problem

With regards to Hominoidea which comprises of apes and human beings, Dixon (2012) alludes to the fact that the social lives of members of this group are quite complex. This also exhibits differences in their sexual behavior with similarities as well as differenced being drawn from the examinations. For instance, chimpanzees and Bonobos live in flexible fusion-fission communities with a multi-male multi-female mating system. Female chimpanzee mate with multiple male partners during the fertile period and the male will likewise mate with multiple females. Sexual relationships are highly labile and thus short term in nature with little or no attachments between partners (Dixon 2012). This is significantly different from human beings for instance. Gorillas by contrast to chimpanzees are polygamous in nature with males (silver-black) competing to lead small groups of females. Successful/dominant males have considerable mating and reproductive success. A DNA typing study of mountain gorillas revealed that dominant males sire 85% of the offspring in their groups (Bradley et al. 2005). The Orangutans, on the other hand, are largely monogamous and while cases of extra-pair copulations occur, the majority of the offspring are sired by the resident male in the family. The increased studies in the sexual behavior of primates have elicited and continue to elicit interesting facts about the behavior patterns of the primates (Thompson-Handler et al., 1984; de Waal, 1987; Furuichi, 1992; Kano, 1989). This study has identified that it is important to examine the sexual relationship behavior of two types of primates, the Bonobos and the Orangutans to clearly point out the similarities and differences in the behavior of respective apes in captivity. The results of the study seek to paint a clearer picture of how these two groups of the primates sexually associate with each other since there are little existing studies painting such a comparative picture.

Research objectives

This study seeks to achieve the following objectives

1. Examine the similarities and differences in sexual behavior of male Bonobos and Orangutans

2. Examine the similarities and differences in sexual behavior of female Bonobos and Orangutans

3. Critically analyze key issues in the sexual behavior of Bonobos and Orangutans

Research hypothesis

This research is premised on the hypothesis that there exist similarities and differences in the sexual behavior of Bonobos and Orangutans and other issues shape the sexual behavior of the members of these families.

Chapter 2: a literature review

2.1: introduction

A literature review is the section of research that explores crucial and significant studies relevant to the research and the researcher analyses these studies in relation to the study objectives. This study examines the study objectives in detail by analyzing relevant supporting literature from the previous studies. The chapter will begin by discussing the similarities and differences in male sexual behavior, followed by female sexual behavior. Other sexual behavior common among the primates will also be examined in this chapter.

2.2: similarities and differences in male sexual behavior

Sexual behavior among the Bonobos and Orangutans appears to be dynamic and is based on the typical lifestyles of each class of the primates. Studies have examined the behavior of males in each of these classes during pre-copulation, copulation or post-copulation periods and a number of similarities have been recorded. First, competition between males for the female mates is real in both Bonobos and Orangutan males. Often, males take on each other in a challenge to win the females who in most cases copulate with the emerging victor (Kano 1989; Dixon 2012). Although there are differences in terms of the strategies adopted by both dominant and weaker males in order to win the females, fights often occur among males over females. The second similarity in the sexual behavior of males in both bonobos and Orangutans is exhibited when dominant males have an advantage over weaker males and thus enjoy mating rights with females. In this case, females tend to be receptive to dominant males and in turn, the dominant males would restrict weaker males from accessing females (Thomson-Handler 1984). This allows them to mate frequently with females in their group since there is little competition from the weaker males. Third, in both Bonobos and Orangutan families, mating are engaged in both for conception and non-conception. Thus, it is common for males to mate with lactating females for instance. However, such engagements tend to be male initiated and forceful on females who surrender to the males often occasioned by a battle between the two (Dixon 2012). The other common similarity in both Bonobos and Orangutans male sexual behavior is the fact that weaker males tend to prey on females (Dixson2015). Studies have revealed that even in instances where the dominant male has the copulation rights, weaker males have occasionally preyed on the females and in numerous occasions successfully copulated with them (Higham et al 2012). However, as studies point out, females too have contributed to this by seeking out and mating with weaker males. Despite the above similarities, there are quite a number of differences in male behavior exhibited by males in each class. First, among the Orangutans, flanged males initiate efforts through the use of ‘long calls’ which serve as both spacing mechanisms for defining their territories and warding off potential male intruders and also locate the females (Drea 2015). Receptive females in response to these calls will either physically follow the calls and locate the flanged male or send a responding call to accept the flanged male to associate with them. Weaker or un-flanged males resort to actively look for females. This is quite contrary to the Bonobos who due to their multi-male multi-female culture make acoustic sounds for sexual communication. The dominant male will then freely copulate with the females in their groups. However, in response to the dominant male, the Bonobo weaker males often make alliances to challenge the dominant males and get chances to mate with the females (Fox 2011).

With Orangutans, flanged males upon meeting the females often display consort ship which involves spending most of the time together with the female mate and publicly displaying their company. This consortship, as studies have revealed may last for several days, weeks or even last for up to a month, though the average period is between 5-6 days. During these interactions, copulation might occur and this also serves as a strategy by flanged males to mate-guard their female partners. This, therefore, puts the Orangutan flanged males copulation advantage over other un-flanged males (Fox 20011). The situation is however different with the Bonobos who, according to the studies, mating and reproduction success appear to be independent of rank and thus, though there might be a dominant male in the group, the battles from the alliances of weaker males gives them a chance to fairly compete with the dominant male for copulation(Thomson and Wangham 2008). Flanged males often engage in extra- consort copulation with other females in the group due to their dominance and lack of active competition from un-flanged males (Nudier 1988). However, studies also revealed tolerance by un-flanged males by flanged males was occasionally observed.

2.3 Similarities and differences in sexual behavior among females

Like their male counterparts, females in the Bonobos and Orangutans play a significant role in sexual relationships and exhibit distinct behavior to influence mating and copulation. Being from two different lifestyles, with Bonobos living a communal lifestyle and the Orangutans leading a semi-solitary lifestyle (Dixson 2015), it is interesting to point out that there are key similarities in the female sexual behavior in both families. First, sexual skin swellings play a vital role in signaling and controlling the reproductive phases of female primates (Muller et al 2007). The Bonobo and Orangutan females develop sexual skin swelling where the skin around the female genitalia develop during the follicular phase and changes in size, shape, color, and turgidity in different cycles of the MSP. Studies have however revealed that Bonobo females often exhibit exaggerated swellings with some lasting longer past the MSP (Heisterman et al 2001). The grounded signal hypothesis explains that variations in exaggerated swellings are relative to the probability of ovulation since, in some instances, ovulations have occurred past the MSP, this prolongs the sexual swellings. Females have been recorded to resume sexual skin swellings after parturition which lasts for about 1-2 years in Bonobo females after delivery. Females have also been involved in the selection of mating partners and even confuse paternity for their infants (Higham et al 2012; Thomson and Wagham 2008). Response to a long call from a flanged male by female among the Orangutan is seen as the primary way females choose their male copulation partners. Bonobos females exhibit a diverse behavior in relation to the choice of mates. This can occur by responding to acoustic mating calls from the male counterparts to choosing the partner to mate with among the group of males in the community. Sexual receptivity is attributed to females in both the bonobos and Orangutan family (Surbeck et al 2012). However, the exact behavior significantly differs. Among the Bonobos, females in the community exhibit extended sexual receptivity and mating are polygynous and polyandrous (Higham et al 2012). The Orangutans, however, tend to choose association with the flanged males and mate with one partner for a consortship period. However, there are some exceptions.

Sexual promiscuity is another behavior exhibited by females in both families. Among the bonobos, females mating with different males is a common phenomenon due to the fact that males do not claim ownership of females (Kano 1989). This allows females to mate with multiple males in the community. The multi-male multi-female lifestyle further supports their behavior. In contrast, female promiscuity among the Orangutan females occurs in a different form. Flanged males usually mate-guard and protect their females against other males during the mating and copulation period. Despite the mate-guarding attempts, females often mate promiscuously with both flanged and un-flanged males (Knott 2001; Fox 2002). The mating of females with the flanged males is largely cooperative and in most instances, unflanged males prey and forcefully mates with the female. Studies have revealed that in some instances, however, females have chosen to mate with un-flanged males by displaying perceptivity towards them and resisting the mating attempts from flanged males. Females have played a significant role in manipulating mating success with male counterparts. Both Bonobos and Orangutan females have significantly influenced the copulations success to favor their desired choice. The Bonobos females have used the exaggerated sexual swelling to confuse males giving them an upper hand of choosing who would father their children (Surbeck et al 2012). Among the Orangutan, however, though flanged males have higher copulation chances, females have used the promiscuous mating pattern to give the un-preferred, un-flanged male mating success and copulation (MacKinnon 1974). The occupation of the social rank points to the main differences between the Bonobo and the Orangutan females. Among the Bonobos, females are often dominant over males and occupy higher social ranks in the community. This gives them the decision making authority over males in the lower ranks and in turn plays a vital role in the sexual behavior in the community. First, females occupying higher social ranks determine the mating with males and can choose the males to mate with (Heistermann et al 2007). Secondly, due to the prolonged mother-son relationships, females often use their power to defend their sons when attacked by other males and this closeness increases the mating success of their sons with other females in the group. However, this is so different from the Orangutan where females occupy the lowest ranks and always subject to males and thus submit, either receptively or forcefully to the demands of males, sexual, to be specific.

Among the Bonobos, co-feeding and coalitions among unrelated females are often facilitated by sexual interaction. These bonds reduce the relative power of males and overall intensity of intra-community injury producing aggression. In this family of primates, mating between males and females is often enhanced by the search for foods and the coalition among females seeks to establish peace among males especially in aggressions related to mating (Thomson-Handler 1984). The Orangutan females, however, exhibit totally different patterns. They often travel in pursuit for long calls for mating from other dominant males in the neighborhood and often abandon their current flanged males in pursuit of new partners (Mapple 1980). In this case, they often orchestrate a male-male encounter and aggression where dominant males battle out and the winner gets the right to mate and copulate with the females.

Other sexual behaviors among the Bonobos and Orangutans

Homosexuality: this is a behavior that has been observed in primates. The Bonobos and the Orangutans, both in captivity and in wild have exhibited behaviors of homosexuality (Hrdy 1988; Rodman and Mitachi 1986). Among the Bonobos, female-female sexual mountings are quite common. Among the Orangutans, male-male mountings have been observed. Though the reasons for homosexuality among these primates are difficult to explain and justify, studies have explained that the occurrence of homosexuality among the primates doesn’t eliminate a heterosexual form of sexual behavior (Dixon 2012). The primates remain heterosexuals with male-female mating both conceptive and non-conceptive being the priority adult primates. Sexual exploration and development: throughout the growth and development, primates have explored their sexuality as they grow. Infants have grown and socialized to have a keen interest in sexual behavior. Orangutan and Bonobo infants have often witnessed mature males mating with females (Knott 2001). Additionally, they have also engaged in activities to explore their sexuality. Among the orangutans, masturbation is quite common among the infants where they have either solitarily explored their genitals or have masturbated other cross-sexual peers (Drea 2015; Dixson 2015). Adult-immature sexual interactions are also common among the Bonobos and Orangutans. For instance, sons have occasionally mounted themselves on their mothers, while mature adults, especially the weaker males have sexual encounters with young females.

Conclusion

This chapter has provided an in-depth exploration of the sexual relationship among the primates with the focus on Bonobos and Orangutans. In so doing, the study has identified key similarities of sexual behavior among the Bonobos and Orangutan males and females. From the discussion, it can be noted that male-male competition for mating is quite common with both dominant and weaker males adopting strategies to maximize their mating chances and copulation. Females, on the other hand, have exhibited alignment with dominant males and involved in determining the mating success of the male counterparts. The respective lifestyle patterns among the families have justified the sexual behavior among the Bonobos and Orangutans. Finally, other homosexuality, masturbation, and adult-immature sexual interactions are also common to members of the two primate families

Chapter 3: research methodology

3.1: introduction

This chapter presents the tools and systems used in the study. Specifically, the chapter explains the research approach, data collection approaches, research design as well as how reliability and validity are achieved in the study.

3.2: research approach

A research approach is an action plan that directs the research in a systematic manner. Qualitative (unstructured), quantitative (structured) and mixed methods are the three main approaches in research (Creswell 2009). In order to find appropriate results as envisioned in the study objectives, all researches have to follow a systematic approach. Williams (2007) explains that researchers normally select the qualitative approach in studies requiring textural data, quantitative approach in those requiring numerical data and mixed method for those studies involving both textural and numerical data. Furthermore, social researches are largely qualitative since certain aspects of study such as behavior cannot be quantified. For this reason, this study will adopt a qualitative approach. Various characteristics of behavior shall be compared and contrasted critically in line with the study objectives. Specifically, the study subjects will be observed and grouped into male or female, Orangutan or Bonobo and the respective sexual behavior observed recorded. From this categorization, similarities and differences will be established between the two groups or among members of the same group. This will then be presented in data analysis and findings. The most commonly observed behaviors of the subjects will be accorded a higher score and comparisons drawn from the behaviors observed among the Bonobos and Orangutans vis-à-vis the studies presented in the literature review. The logit model (maximum likelihood approach) testing will be relied upon during data analysis

3.3: data collection

Data are raw facts that have not been organized, processed or analyzed and virtually have less meaning and few benefits. Mohajan (2016) describes data as structured or unstructured, with little information to be used in a specific context. Researchers have to identify and use these data to generate valuable information that can be presented to support facts and justify their respective studies. This study utilizes secondary data by collecting, processing and analyzing data from previous relevant studies conducted and published by other researchers.

3.4: research design

A research design is a blueprint for the collection, processing, measurement, and analysis of data (Kothari 2004). In this study, the researcher has defined study objectives and hypothesis and seeks to test the hypothesis using critical analysis of experimental findings relevant to the study.

3.5: reliability and validity of the study

Validity in research is concerned with the truthfulness and accuracy of scientific findings (Hashim et al 2007; Robson 2011). This describes how well the data collection and analysis of the research captures the reality being studied. Reliability is concerned consistency, dependability, and replicability of the study in research (Neuman 2012; Cresmell 2009). To enhance reliability and validity, this study will be focused on collecting and analyzing data only from studies that have been published by other researchers.

3.6: ethical issues in research

Ethics is a vital tool in research. Ethics is maintained in this study by upholding the integrity of the study whereby appropriate techniques and methodologies have been considered throughout the study. Potential risks anticipated in the study includes exposure to extreme environmental conditions while observing the subjects, perceived aggression from the Subjects and difficulty in clearly observing the sexual behaviors of these primates. Additionally, the observation of sexual behavior of the subjects may occasion to observing the animals mating and reporting such behavior raises ethical concerns in terms of terminologies used.

Conclusion

This chapter presented a detailed framework that shall guide the study. The researcher outlined that the qualitative approach shall be adopted in data collections and analysis, with the representation of information in tabular and diagrammatic forms to aid analysis. Data shall be collected from the secondary sources with a commitment to observing the ethics of the study and enhance the reliability and validity of the study findings.

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