Mechanism of birth in chimpanzees: humans are not unique among primates

Abstract

Researchers have argued that the process of human birth is unique among primates and mammals in that the infant emerges with its face oriented in the opposite direction from its mother (occiput anterior) and head rotation occurs in the birth canal. However, this notion of human uniqueness has not been substantiated, because there are few comparative studies of birth in non-human primates. This paper reports the mechanism of birth in chimpanzees (Pan troglodytes) based on the first clear, close-up video recordings of three chimpanzee births in captivity. In all three cases, the foetus emerged with an occiput anterior orientation, and the head and body rotated after the head had emerged. Therefore, these characteristics are not uniquely human. Furthermore, in two of the three cases, the chimpanzee newborns landed on the ground without being guided from the birth canal by the mother. The fact that the human newborn emerges with an occiput anterior orientation has thus far been taken as evidence for the necessity of midwifery in modern humans, but this view also needs revision. Our observations raise the need to reconsider the evolutionary scenario of human birth.

Comparative primate obstetrics: Observations of 15 diurnal births in wild gelada monkeys (Theropithecus gelada) and their implications for understanding human and nonhuman primate birth evolution

“…Some have argued that this fetal emergence pattern (long considered unique to humans; Weaver & Hublin, ) appeared after Homo diverged from Australopithecus (Franciscus, ; Rosenberg & Trevathan, ; Ruff, ; Tague & Lovejoy, ; Trevathan, ; Weaver & Hublin, ). Others argue that the shift occurred much earlier (Berge & Goularas, ; Berge, Orban‐Segebarth, & Schmid, ), a view recently corroborated by observations of three captive chimpanzees giving birth to infants in the occiput anterior position (Hirata et al, ). Our finding that gelada infants are routinely born facing the mother's face is consistent with the hypothesis that the shift to the occiput anterior fetal emergence pattern typical of humans occurred after hominoids (hominins and great apes) separated from Old World monkeys.…”

“…Despite their importance, the events surrounding parturition remain poorly understood in wild nonhuman primates (Caine & Mitchell, ; Rosenberg & Trevathan, ; Trevathan, ). Behaviors surrounding birth have been well documented in a few captive primates (e.g., patas monkeys: Chism, Rowell, & Richards, ; chimpanzees: Elder & Yerkes, ; Nissen & Yerkes, ; cynomolgus monkeys: Timmermans & Vossen, ) and reports from captivity have provided important insights into the evolutionary mechanics of the birth process (e.g., Hirata, Fuwa, Sugama, Kusunoki, & Takeshita, ; Stoller, ). However, captivity and provisioning can alter animal behavior and bodily functions (reviewed in Costa & Sinervo, ; Fusani, Canoine, Goymann, Wikelski, & Hau, ), so studies of the birth process from a greater diversity of wild primate populations are needed to advance our knowledge of the social and ecological factors that have shaped primate births.…”

“…Nocturnal births are thought to be adaptive in diurnal species because they enable females to give birth when their group mates are at rest, thereby preventing females from being left behind and reducing their vulnerability to predation and agonism from conspecifics (Duboscq, Neumann, Perwitasari‐Farajallah, & Engelhardt, ; Jolly, ). For species that build sleeping nests, like chimpanzees, there is the added benefit that a nest can act as a safety net if the infant falls during delivery (Hirata et al, ).…”

“…Despite the importance of the birth process, we know surprisingly little of the factors that have shaped the evolution of these five defining attributes of human births. Unfortunately, few studies have compared patterns of birth among nonhuman primates to those of humans in key areas of evolutionary interest, including infants' orientation when emerging from the birth canal, maternal or conspecific aid to infants during delivery, or maternal consumption of the afterbirth (Hirata et al, ; Rosenberg & Trevathan, ; Trevathan, ; Turner et al, ). Comparative data from studies of wild nonhuman primate births can potentially shed light on the extent to which the unusual features of human births were outcomes of the hominin shift to habitual bipedalism and big brains (Trevathan, ).…”

From PPROM to caul: The evolution of membrane rupture in mammals

“…B. Chimpanzee and neonate with ruptured gestational sac (Hirata et al, 2011). Image by permission of The Royal Society (http://www.youtube.com/watch?v=dfd0fzX9M5g).…”