BS&M returned this past Friday and, alas, I couldn’t attend. Luckily, the discussion centered on the Cretan footprints paper that guest blogger Sarah Hlubik covered in our last post, so you guys aren’t missing out on sweet, sweet new paper coverage.
What apparently went down on Friday was a lot of talk about bears. Were there bears in the area during the Miocene? Yep and yep. Can bears walk upright? Yep! What do bear tracks look like? Like this (according to one site, anyway). Does this mean we need to change our name to Bears, Stones, and Monkeys?
It seems the BS&M crowd is fairly skeptical about the claim of bipedal primate footprints in the Miocene, but loves them some possible bearpedality (thanks for that one, Fred). Personally, I’d love to see the authors find some body fossils of any potential candidate track-maker – and if it’s a primate, even better!
Until next time, I leave you with this (credit to Alex Pritchard):
So, the big fossil news that the Leakey Foundation was teasing when last I posted? It was this:
BS&M Blog readers, meet Nyanzapithecus alesi, a new 13 million-year-old Miocene ape from Kenya. HOW COOL IS THAT?!
I will tell you how cool. VERY COOL. I’m biased (as always – because I pick the things I want to write about for the blog, which are things that I think are very cool), but seriously. There are a bunch of reasons this discovery is awesome, like:
3) You also rarely find infant material in the primate fossil record. (Yes, I know, the Taung Child is an exception to this rule, too.) Infant bones are smaller and more fragile than those of adults, which makes them even less likely to fossilize and be recovered later.
Alesi is also awesome, simply by virtue of being a Miocene ape (my Miocene bias is definitely showing). The Miocene (23-5.3 mya) often gets called a “planet of the apes” because there was a huge diversity of hominoids (the fancy taxonomic group name for apes, including us, is Hominoidea) that lived through Europe, Africa, and Asia at that time. Which is SUPER AWESOME because they were “experimenting” with different types of locomotion at that time (which is totally my jam), but also makes it really hard to tell our potential ancestors from our side-branch cousins. A classic problem for people who work on Miocene apes is that they have ape faces and monkey bodies, and the field disagrees about which is more important (the face or the body) for figuring out who is related to who. Hopefully one of the authors of the Alesi paper (shout out to Kelsey Pugh!) will be able to work some of these relationships out with her dissertation research.
My final thought/question (for now) on Alesi is: the authors suggest that gibbon-like features evolved in parallel several times in different branches of the hominoid lineage – why couldn’t these features be ancestral, rather than derived? If that was the case, it would just require that a different set of facial features evolved in parallel instead. So why the gibbon-like ones and not the other ones?
That’s all for now! Hopefully BS&M will be back on September 8th – catch you then!
August has arrived, the summer is winding down, and those anthropologists lucky enough to be off doing fieldwork have started to come home. A new academic year will begin soon and, with it, the official resumption of the Bones, Stones, and Monkeys journal club! I’m looking forward to getting some new, interesting discussion posts going, but for now, two more pieces of anthro news.
This week’s news comes from the world of #scicomm (aka, public science communication). Science communication/outreach is definitely picking up steam as a major movement lately (though it has always been important) and some excellent #scicomm is being done by anthropologists. We’re lucky enough to study something that people always seem to find interesting – themselves!
First up, Dr. Julienne Rutherford (U. Illinois – Chicago) gave a public radio interview about how modern birth practices might affect human evolution. The overarching question this type of research is trying to answer is, essentially, how does culture interact with and shape biological evolution. Humans babies have relatively large heads compared to those of most other primate babies, which tends to make giving birth difficult. We’ve gotten around the complications of this issue culturally via C-section, but before surgical interventions were possible the size of a baby’s head was a serious selective pressure on birth canal size – too large a head could mean death for both mother and infant. With that pressure removed, Dr. Rutherford suggested that we could potentially see even more variation in female pelvis/birth canal size and somewhat bigger-headed (though not super genius) babies as a result. I’d be curious to see estimates of how long it might take for infant head size/female pelvis size and shape to decouple, given that there has been some cool previous research on how these two things are linked.
Next up, Dr. Caroline VanSickle threw down about “manspreading.” Spoiler alert – it’s a cultural phenomenon, not a biological one. Basically, an emeritus kinesiology professor suggested in an interview that manspreading is the result of sexual dimorphism (sex-related differences in appearance/shape/size) between the male and female pelvis. Specifically, the narrow pelvis of men causes their hip joints to pinch when their knees are together – an issue that is allegedly alleviated by manspreading. Dr. VanSickle shoots this down as not being a biological reality. Behavior isn’t determined by one’s skeleton, which changes during life depending on what you do with it. We call this Wolff’s Law (and I’m probably biased in my enthusiasm for her invocation for it – my entire dissertation was on Wolff’s Law and the pelvis). In addition to being able to shape your skeleton with your behavior, she also mentions research showing that manspreading does not occur in all cultures or with the same frequency between cultures. Personal bias aside, Dr. VanSickle’s case against biological determinism as an excuse for rude behavior was nicely made, so let’s all just keep our knees to ourselves on public transportation, okay?
That’s all I’ve got today from the world of anthro news! The Leakey Foundation tweeted today that they have “exciting fossil news to share tomorrow,” so stay tuned!
Disclaimer: I know Caroline (as I’ve said before, the pelvis world is small). She’s still right.
Further Reading Fischer, B., & Mitteroecker, P. (2015). Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma. Proceedings of the National Academy of Sciences, 112(18), 5655-5660.
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.
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.
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.
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.