Anthro News

Chimpanzee super strength!

Things around the blog have been a bit slow with BS&M on its summer hiatus (and me teaching an intensive summer human osteology course), but new anthro papers continue to come out!

What I’ve been reading:

Chimpanzee super strength!
Matthew O’Neill and colleagues tested the claim that chimpanzees are “super strong” relative to modern humans using a combination of actual chimpanzee muscle samples and computer modeling. Spoiler alert – they’re only about 1.35 times stronger than we are, and the reason for this has to do with both muscle fiber type and fiber length. Chimps have more “fast fibers” than we do, along with longer fibers, which the authors suggest make their muscles capable of greater maximum force output and power than ours. This might be beneficial for a large-bodied, arboreal primate. But not all arboreal primates have skeletal muscle dominated by fast fibers; O’Neill et al. also point out that the slow loris has, like we do, muscle that is mostly made up of slow fibers. And, based on their comparisons to other mammals, the authors suggest that our slow, short muscle fibers likely evolved within the hominin lineage, making them a unique characteristic of our group.

So what this means from an evolutionary perspective is that sometime over the last 7-8 million years, potentially coinciding with our shift toward obligate (full-time) upright bipedalism, the architecture of our muscles changed along with our skeleton. This is super cool because soft tissue anatomy isn’t preserved in the fossil record (except in certain rare, extreme conditions, and never in hominins) and this gives us a way to potentially investigate it. I also have some purely self-serving questions/ideas about how this relates to my own research interests, but I think I’ll stay quiet about them for the time being.

In other Anthro News: if you’re in the area and haven’t been, check out the Philadelphia Zoo. They’ve got some very cool primates (omg, red-shanked douc langur) and the Zoo360 Animal Exploration Trails are awesome. The family of gibbons was hanging out in one when I was there and watching the baby do its hilarious little bipedal run up close was incredible.

Reference
O’Neill, M. C., Umberger, B. R., Holowka, N. B., Larson, S. G., & Reiser, P. J. (2017). Chimpanzee super strength and human skeletal muscle evolution. Proceedings of the National Academy of Sciences, 201619071.

A Plethora of Pelvis Papers

Part 1 – The Ilium

The pelvis is the coolest skeletal element. I might be slightly biased, given that I wrote my dissertation on it. But probably not – it is, objectively, the coolest.

Why is the pelvis so cool? Because it can tell us a lot about how a primate walks around and gives birth, while simultaneously being super complicated to try to figure out.

Recently, two special issues of the scientific journal The Anatomical Record were published focusing exclusively on the pelvis. It was like your gift-receiving holiday of choice for pelvis nerds like me. (And, really, there can never be a true plethora of pelvis papers; the more pelvis papers, the better!) I’m finally getting around to reading them, so I figured I’d do a short series of posts on some of the ones that particularly interested me, starting with one on the ilium.

But first, a quick primer on the pelvis:

The pelvis is made up of two innominates (hipbones) and the sacrum/coccyx (tailbone). The two hipbones are themselves made up of three bones each (the ilium, ischium, and pubis) that fuse within the socket of the hip joint (called the acetabulum, which is Latin for “little vinegar cup”) around ages 16-18.

male pelvis
A complete male pelvis (Gray 1918)

Anthropologists really dig the pelvis because ours is highly modified for walking on two feet (bipedalism), so it looks very different from the pelvis of our closest living relative, the chimpanzee.

schultz primate torsos
The trunk skeletons of a macaque, gibbon, chimpanzee, and human (left to right) (Schultz 1950).

The trend in paleoanthropology recently has been to think of our last common ancestor (LCA) with chimpanzees as being more chimp-like than human-like (though there are some who have argued against this, like the team that discovered Ardipithecus ramidus). So what might this mean for the anatomy of the pelvis of the LCA? Was it more chimp-like or more human-like, and how can we test this?

Hammond and Almecija set out to answer these questions in their contribution to the May special issue (“Lower Ilium Evolution in Apes and Hominins”). They focused on the lower ilium because it varies in length between primate species and the variation has been suggested to be related to differences in how different species move around. They used a combination of measurements, statistics, and tree-building programs to look at variation in lower ilium height within and between species, tried to reconstruct the pelvic anatomy of progressively older LCAs (including the chimp-human LCA and the LCA of all of the living apes), and then compared those reconstructions to some of the predictions that the Ardipithecus team made about the evolution of the pelvis when they published that fossil.

What they found (based on a really large sample of pelvic measurements from 58 humans, 112 great apes, 61 gibbons/siamangs, 95 Old World monkeys, 33 New World monkeys, and 8 fossils), was that the variation they saw in lower ilium height was not purely size-related, which suggests that there might be functional or evolutionary reasons behind it. They also found that gorillas have ilia that might resemble the primitive condition for all hominoids (apes + hominins) and that the chimp-human LCA probably had a shorter lower ilium than living chimpanzees, as had been suggested by the Ardipithecus team. What this means is that living chimpanzees and orangutans may have both independently evolved long lower ilia, which complicates our use of parsimony when building evolutionary trees; sometimes shared features don’t come from a common ancestor, but evolve (via similar pathways, from similar structures) in two related taxa due to similar pressures.

So what’s the take-home message? Well, a lot of people have suggested that there is a characteristic “ape-like” long lower ilium that is somehow functionally related to their locomotion, but that doesn’t seem to actually be the case. The innominate is a complicated bone and it’s not just how a primate gets around that influences it.

Also worth taking home: the pelvis is super cool and so are fossil apes.

If you dig the pelvis, stay tuned! This is the first post in what will be a short series on the pelvis. (Maybe short. Maybe not. Much like the evolutionary history of the lower ilium.)

Disclaimer: I have met/know the authors of this paper. And I’d be just as excited about it even if I didn’t because the lower ilium needs all the love it can get.

Reference
Hammond, A.S. and Almécija, S. (2017). Lower ilium evolution in apes and hominins. The Anatomical Record, 300(5), 828-844.