Human babies are regularly born facing the opposite direction of their mothers, a position that has often been reported to be unique to our species (Rosenberg & Trevathan, 2002). In a recent report in the journal Biology Letters, Satoshi Hirata, Koki Fuwa, Keiko Sugama, Kiyo Kusunoki and Hideko Takeshita of the Great Ape Research Institute of Hayashibara Biochemical Laboratories in Okayama, Japan report that chimpanzees also give birth to offspring in a similar position, a position called “occiput anterior”. Joseph Milton of Nature magazine reported that, “The discovery…calls into question the argument that backwards-facing babies were an important factor in the evolution of midwifery in humans.”

It has long been suggested that the regular practice of human females receiving assistance during childbirth is unique in our species and due to the typical position of human infants during the process (Rosenberg & Trevathan, 2002). Mechanically, human infants need to rotate during labor and emerge with their faces opposite those of their mothers to most effectively protect their brains. However, it has been assumed that this position makes it difficult for mothers to give birth on their own, because they can’t reach back and clear an airway for their new infants (Rosenberg & Trevathan, 2002). The result, some have argued, has been a long history of midwifery, or helpers, throughout the course of human evolution.

Hirata et al’s report has started a debate about the presumed uniqueness of human birth and what it means if chimpanzees have similar births. Interestingly, their report, which is causing so much uproar, is of three births in captivity. To further complicate matters, the researchers report to having been in the enclosures with the chimpanzees when they gave birth. While it is almost certain that their presence did not impact the orientation of the infants during labor, it is still highly irregular and not objective science. The sample size in this report, however, is a different story. Sample sizes are critical to help ensure that observations are not of anomalous phenomena. While I doubt that these three chimpanzees all had infants in irregular positions, more data is needed before conclusions can be drawn about species typical patterns during child birth in chimpanzees. Beyond this new information on childbirth in chimpanzees, more data is needed on childbirth in the other ape species. Given the long history of apes in captivity in zoos and sanctuaries, it’s surprising that those data are not already known.

If the data from this current study hold up over time, just what does it mean for studies of human evolution? Trevathan originally hypothesized that the orientation of human infants during delivery is part of the unique adaptive suite of encephalization and pelvic shape in humans, and that it was directly connected to the notion of helpers during labor (something also proposed to be unique to humans). Some researchers have taken that notion of helpers to develop hypotheses about midwifery and its history in the human lineage. While statements like the “…evolution of midwifery” are a little fanciful, most researchers agreed that the orientation of human infants during delivery, combined with the orientation of the pelvis and the difficulty of modern childbirth make it difficult for human females to deliver on their own. While it’s true that most female primates give birth on their own, there have been reports of helpers assisting during childbirth in common marmosets (Rutherford, personal communication).

One thing that was unknown before this report, and is still not completely resolved, is when the occiput anterior orientation of human infants first emerged. If these data are confirmed by further studies it could mean that this position, once thought to be unique to humans has a deep evolutionary history, or that it represents variation across primates. Simply put, we need more data to be able to say whether or not this pattern is unique to chimpanzees and humans, unique to humans, chimpanzees and bonobos, or a more generalized pattern seen in other primates. For studies of human evolution, it doesn’t shatter any paradigms, but it should serve as a lesson: We need to be as complete as possible in our data collection, as thorough as possible in our analyses, and as careful as possible in our conclusions.

As we gather more and more data, on more and more different primate and animal species, we continue to see that humans are not unique after all. Instead, the pattern that is emerging is that humans share so much in common with the other primates that the line between the two is a blur. The one thing that is clear is our place in nature. We are apes, primates, mammals, vertebrates, and the product of evolution by natural selection.

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