The find dates to 0.9-1.4 million years ago and is nearly complete. Also found were the sacrum and last lumbar vertebra. A number of traits link the pelvis to H. erectus, these include a robust iliac pillar, sigmoid shaped iliac spine, transversely broad with laterally flaring ilia. The sacrum has alae that are anteroposteriorly broad and has a robust sacral tuberosity.
The find has attracted a lot of attention for several reasons. First, the pelvis is that of a female – based on a wide greater sciatic notch, subpubic angle, ventral arc – and stature estimates indicate the she was quite short and had a broad trunk. This indicates that sexual dimorphism was greater than some had thought. I say some because the discovery of KNM-ER 42700 last year and KNM-OL 45500 four years ago indicate that there is more to the body size story. Previously, and based in large part on the KNM-WT-15000 skeleton H. erectus was though to be adapted to tropical environments and/or endurance running. The new pelvis (dubbed BSN49/P27) does not display adaptations for either of these. Second, the find has some implications for the evolution of the human brain and life history. Those of you who read my post on Neanderthal life history will know some of the basics. What we would like to know is how big of a baby could H. erectus birth? The answer to that question will tell us something about how their brain grows. Simpson et al estimate that BSN49/P27 could have birthed a baby with a brain volume of about 300-315 ml. This is about 30-50% that of an adult. By comparison, chimps are born with brains ~40% that of an adult, while humans are born with brains ~24% that of adults. In chimps this figure rises to ~72% by age three, while humans don’t reach this value until age five. An alert reader may remember this post, where I linked to several papers that discussed this issue based on endocranial capacity of the Mojokerto child. At any rate, my take on it is that this new estimate seems to support Leigh’s position – although I haven’t quite made up my mind about it. There are some confounding variables, such as maternal body size, energetics, and nutrition that have make things a little more difficult (and I will have more to say about that in a couple of posts in the near future).
As an added sidenote, if you ask a creationist pain in childbirth is all due to Eve eating an apple. The problem is that some species of macaques, some species of capuchins, and squirrel monkeys all experience the cephalopelvic issues humans face, so one would like to know what they did to piss God off…
Posted on November 23, 2008 by Afarensis, FCD