Male mammals show a diverse array of mating bonds, including obligate monogamy, unimale and group polygyny and promiscuity. These are associated with a wide variety of different forms of mate guarding, including the defence of feeding and mating territories, the defence of female groups and the defence of individual receptive females. Female mating bonds include long-term monogamy, serial monogamy, polyandry and promiscuity. Both male and female mating behaviour varies widely within species. Variation in male mating behaviour is related to the effect of male assistance in rearing young and to the defensibility of females by males. The latter is, in turn, related to female ranging behaviour and to the size and stability of female groups. Much of the variation in mammalian mating bonds and systems of mate guarding can be attributed to differences in these three variables.

Mammalian mating systems.

A reconceptualization of stigma is presented that changes the emphasis from the devaluation of an individual's identity to the process by which individuals who satisfy certain criteria come to be excluded from various kinds of social interactions. The authors propose that phenomena currently placed under the general rubric of stigma involve a set of distinct psychological systems designed by natural selection to solve specific problems associated with sociality. In particular, the authors suggest that human beings possess cognitive adaptations designed to cause them to avoid poor social exchange partners, join cooperative groups (for purposes of between-group competition and exploitation), and avoid contact with those who are differentially likely to carry communicable pathogens. The evolutionary view contributes to the current conceptualization of stigma by providing an account of the ultimate function of stigmatization and helping to explain its consensual nature.

https://courses.washington.edu/pbafhall/514/514%20Readings/evolutionaryoriginsofstigma.pdf

Evolutionary origins of stigmatization: the functions of social exclusion.

Handbook of Parenting. Volume 2: Biology and Ecology of Parenting. Second Edition.

Hunting is often considered one of the major behaviors that shaped early hominids' evolution, along with the shift toward a drier and more open habitat. We suggest that a precise comparison of the hunting behavior of a species closely related to man might help us understand which aspects of hunting could be affected by environmental conditions. The hunting behavior of wild chimpanzees is discussed, and new observations on a population living in the tropical rain forest of the Tai National Park, Ivory Coast, are presented. Some of the forest chimpanzees' hunting performances are similar to those of savanna-woodlands populations; others are different. Forest chimpanzees have a more specialized prey image, intentionally search for more adult prey, and hunt in larger groups and with a more elaborate cooperative level than savanna-woodlands chimpanzees. In addition, forest chimpanzees tend to share meat more actively and more frequently. These findings are related to some theories on aspects of hunting behavior in early hominids and discussed in order to understand some factors influencing the hunting behavior of wild chimpanzees. Finally, the hunting behavior of primates is compared with that of social carnivores.

/pdf/hunting-behavior-of-wild-chimpanzees-in-the-tai-national-g77flnxunx.pdf

Hunting behavior of wild chimpanzees in the Taï National Park

Although Trivers' general rule has many exceptions, it accurately identifies the primary source of conflict between the sexes: in most sexual organisms most of the energy and time invested in offspring comes from females . From this basic fact it follows that , for males more than females, reproductive success is limited by the number of matings with fertile partners. For females more than males, on the other hand, reproductive success is limited by the time and effort required to garner and transfer energy to offspring and to protect and care for them (Bateman, 1948; Trivers, 1972). Males therefore are usually more eager than females to mate at any time with any partner who may be fertile , while females are usually more careful than males to choose mates who seem likely to provide good genes, protection, parental care, or resources in addition to gametes (Trivers, 1972; Alexander and Borgia, 1979). Combined with female interest in mate quality, male interest in mate quantity creates a widespread conflict of interest between the sexes (Borgia, 1979; Parker, 1979; Hammerstein and Parker, 1987). The conflict is

Male Aggression and Sexual Coercion of Females in Nonhuman Primates and Other Mammals: Evidence and Theoretical Implications

Demography provides critical data to increase our understanding of the evolution, ecology, and conservation of primate populations. The chimpanzees of the Mahale Mountains National Park, Tanzania, have been studied for more than 34 yr on the basis of individual identification and standardized attendance records. From this long-term study, we derived the following demographic data: The major cause of death was disease (48%), followed by senescence (24%) and within-species aggression (16%). Fifty percent of Mahale chimpanzees died before weaning. The median ages of female life history variables were: first maximal swelling, 10.0 yr (n = 5); emigration, 11.0 yr (n = 11); and first birth, 13.1 yr (n = 5). The median period of adolescent infertility was 2.8 yr (n = 4) when calculated from the age at immigration to that at first birth. Female fecundity was highest between 20 and 35 yr of age, with an annual birth rate of 0.2. Twenty-six females that were observed from a young age (10-13 yr) to death at various ages (15-40 yr) gave birth to an average of 3.9 and weaned an average of 1.4 offspring. Twenty-five females that were observed from middle age (18-33 yr) to death in older age (31-48) gave birth to an average of 2.7 and weaned an average of 2.0 offspring. The post-reproductive lifespan for female chimpanzees was defined as the number of years that passed from the year when the last offspring was born to the year when the female died, minus 5. Twenty-five percent of old females had a post-reproductive lifespan. The interbirth interval after the birth of a son (x = 72 mo) tended to be longer than that after the birth of a daughter (x = 66 mo). The extent of female transfer, which is a rule in chimpanzees, is influenced by the size and composition of the unit group and size of the overall local community.

Demography, female life history, and reproductive profiles among the chimpanzees of Mahale

and Summary

A unit-group (K-group) of chimpanzees has shown a drastic demographic change in the course of 17 years (1966–1983) of field study. K-group had 6 adult males in 1966. Initially, the group lost adult males one by one between 1969–1975. The number of adult males in the unit-group was the main factor influencing the immigration of strange, cycling females and the emigration of cycling females, although nulliparous females born into K-group regularly emigrated to other unit-groups, regardless of the number of adult males within K-group. When the number of adult males in the group dropped to only two in early 1978, many cycling females began to associate with the males of a larger unit-group (M-group), as well as those of K-group. When K-group lost one of the remaining adult males and became essentially a “one-male” group in 1979, all the fertile, cycling females began to associate mostly with M-group and radically expanded their ranges, although their core areas tended to be closer to their original ranges. During this time the “alpha” male of K-group tried to restrict the ranging of “his” females to his normal range with a variety of herding techniques. The extent of the range expansions by immigrant females was influenced by their ages and ages of their youngest offspring. Parous females usually did not transfer or re-transfer permanently as long as their offspring were alive and the number of adult males within their group was more than three. Juvenile males occasionally followed their mothers and transferred between unit-groups. Some males refused to transfer even though their mothers transferred permanently. The destiny of these juvenile males who transferred is not clear, as such cases were rare. Annual ranges of immigrant females roughly coincided with those of the resident adult males of the unit-group. This observation effectively rejects the male-only community model of chimpanzee social organization (Wrangham 1979a). By the middle of 1983, K-group consisted of four animals: one lactating female with her infant daughter and one old post-reproductive female with her adolescent son. The loss of adult males was partly attributed to inter-unit-group aggression. Neighbouring unit-groups expanded their ranges at the expense of a small unit-group with few adult males. The large-scale transfer of cycling females to M-group is regarded as a female reproductive strategy, as such migration may lead to a greater number of available mates, and decrease the possibility of attacks from large neighbouring unit-groups, and moreover the females can still utilize their familiar feeding areas.



Zusammenfassung

Im Verlauf einer 17 Jahre dauernden Feldstudie durchlief eine bestimmte Schimpansengruppe (“K”) drastische demographische Veranderungen. 1966 enthielt sie 6 adulte Mannchen, verlor aber von 1969–1975 eins nach dem anderen davon. Als 1978 nur noch 2 adulte Mannchen da waren, schlossen sich viele der sexuell aktiven Weibchen abwechselnd diesen und den Mannchen der benachbarten groseren M-Gruppe an. 1979 war nur noch ein K-Mannchen ubrig, und alle sexuell aktiven Weibchen hielten sich meist bei den M-Mannchen auf. Dadurch erweiterten sie ihr Streifgebiet beachtlich, behielten aber das Heimatgebiet auserdem bei. Das letzte K-Mannchen versuchte mit verschiedenen Mitteln, “seine” Weibchen in seinem Gebiet zu halten.



Die Zahl der erwachsenen Mannchen in einer Gruppe bestimmt vorrangig das Zuwandern fremder oder Abwandern eigener Weibchen. Nullipare in der K-Gruppe geborene Weibchen besuchten regelmasig andere Gruppen, unabhangig von der Zahl vorhandener Mannchen. Die Grose der Gebietserweiterung abwandernder Weibchen hing von ihrem Alter und vom Alter ihres jungsten Kindes ab. Mutter wanderten gewohnlich nicht dauerhaft ab, solange ihre Kinder lebten und es wenigstens 3 adulte Mannchen in ihrer Gruppe gab. Junge Mannchen folgten gelegentlich ihren Muttern zu einer anderen Gruppe, manche Mannchen aber blieben, auch wenn die Mutter ausgewandert war. Die zugewanderten Weibchen zogen im Jahr ungefahr dorthin mit, wohin die ansassigen Mannchen gingen.



In der Mitte des Jahres 1983 bestand die K-Gruppe nur noch aus 4 Tieren: Einer saugenden Mutter mit ihrer Tochter und einer Greisin mit erwachsenem Sohn. Das Verschwinden der Mannchen ging zum Teil auf Zwischen-gruppen-Aggression zuruck. Benachbarte Gruppen dehnten ihren Wohnbereich aus auf Kosten kleiner Gruppen mit wenigen Mannchen. Das Uberlaufen so vieler Weibchen zur M-Gruppe wird als Fortpflanzungstaktik gedeutet: Die Zahl verfugbarer Paarungspartner wachst, die Gefahrdung durch Angriffe durch grose Nachbargruppen nimmt ab, aber dennoch konnen die Weibchen weiterhin die gewohnten Fresgebiete benutzen.

Group extinction and female transfer in wild chimpanzees in the Mahale National Park, Tanzania.

The mating patterns of free-ranging chimpanzees (Pan troglodytes) of the Mahale Mountains, Tanzania, were studied. Opportunistic mating (non-competitive and temporary mating) was frequently observed in a large-sized unit-group, among young, low-ranking males, and among young, newcomer, non-ovulating females. Restrictive mating (a continuous sexual relationship between a particular pair which includes possessiveness and consortship) was frequently observed in a small-sized unit-group, among middle- and old-aged, high-ranking males, and among old, resident, ovulating females. Relations between those characteristics, such as group size and composition, ages of the individuals of both sexes, female estrous stages, and life history, and the 2 mating patterns are discussed.

Opportunistic and restrictive matings among wild chimpanzees in the Mahale Mountains, Tanzania

Coalitions and alliances in humans and other animals

Long-term demographic observations on a large-sized unit-group of chimpanzees in the Mahale Mountains, Tanzania, are summarized. The unit-group, the M group, contains over 100 individuals, which makes it the largest unit-group ever reported. The age-sex composition, natality, mortality and transfers of the M group are analyzed. An attempt is made to illustrate an age-sex pyramid of the group by estimating the ages of all the individuals in the group. The results reveal that: (1) the mortality rate of the male infants within 1 year almost doubled that of female infant; (2) adult male to adult female ratio of the M group is considerably higher than any other unit-groups elsewhere; and (3) the M group contains a relatively large number of old animals over 40 years of age, suggesting that the longevity of wild chimpanzees might be greater than estimated so far.

Mariko Hiraiwa-Hasegawa

Papers

Demography, female life history, and reproductive profiles among the chimpanzees of Mahale

Group extinction and female transfer in wild chimpanzees in the Mahale National Park, Tanzania.

Opportunistic and restrictive matings among wild chimpanzees in the Mahale Mountains, Tanzania

Coalitions and alliances in humans and other animals

Demographic study of a large-sized unit-group of chimpanzees in the mahale mountains, Tanzania: A preliminary report