Anthro News

Big-headed babies and manspreading

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 Sciences112(18), 5655-5660.

Ghost Lineages Ride Again: the Spit Edition

Guest Blogger: Mareike Janiak

Darcy asked me to write a guest post on “the new spit paper” and it shows that she knows me well. Saliva? Salivary proteins? Functional genetic variation in those proteins? Possible interbreeding with mystery hominins? The microbiome?

Fav_things_gif.gif

The new spit paper” by Duo Xu and her colleagues is titled “Archaic hominin introgression in Africa contributes to functional salivary MUC7 genetic variation” and is going to be published in the journal Molecular Biology and Evolution.

The authors looked at genetic variation in a gene called MUC7, which codes for mucin 7, a protein that is only found in saliva. In an earlier study, they found that the number of times a specific part of the MUC7 gene is repeated varies across different primate species. In gorillas it is repeated only 4-5 times, while vervet monkeys have 11-12 repeats. Humans have 5-6 repeats, but the gene hadn’t been thoroughly investigated in our own species, which is where the current paper comes in.

One known function of mucin 7 is to bind with bacteria in the mouth, so one question the authors asked is whether genetic variation in MUC7 correlates with the type of bacteria found in a person’s mouth. Using data from the Human Microbiome Project the authors found that people that have more similarity in the MUC7 gene also have more similar bacterial profiles (microbiomes) – but only around the mouth. While this is an interesting result, it creates more questions than it answers! Do these different bacterial profiles provide an adaptive benefit? And if so, for what? In what context is it better to have one over the other? Is it dependent on pathogens in the environment or maybe on diet? Lots of great avenues for future research!

But the authors also found something else when they were looking at MUC7 variation across people, something very curious. As expected, they found a number of different patterns of MUC7. These patterns are called haplotypes and they appear as time goes by and (mostly benign) mutations accumulate along the gene. Generally these haplotypes were pretty similar to each other, but (and this is the weird part!) one of them, haplotype E, was totally different.

Most of the MUC7 haplotypes were like these poodles, small differences but all clearly poodles:

regular_poodles

And then there’s haplotype E:

special_poodle

Yes, still a poodle, but also kind of…out there and unexpected.

So what’s the deal with haplotype E?

Continue reading “Ghost Lineages Ride Again: the Spit Edition”

Anthro on TV

I’ll take paleoanthropology for $400.

So this happened on last night’s episode of Jeopardy:

ancient relatives_jeopardy
Photo credit: Zach Throckmorton (@throckman)

Clues included info on bipedalism, fire at Wonderwerk Cave in South Africa, and Homo erectus, among other things (and the full text should be up at j-archive.com in the next few days).

This amused me for a couple of reasons. First, “exam review Jeopardy” is a classic recitation section technique for TAs and it’s not often that we can use a real Jeopardy set of clues for it. And second, this was from Thursday night’s episode of Jeopardy and I was a contestant on Tuesday night’s episode. SO CLOSE and yet so far.

I’ll be keeping my eye peeled for more anthro in pop culture; maybe it will become a recurring blog theme!

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.

Who Were the Oldest Homo sapiens?

Guest Blogger: Rene Studer-Halbach

Jebel Irhoud 1
The cranium of Jebel Irhoud 1, the original specimen discovered by miners in 1961. Modified from Bruner & Pearson (2012)

On June 8 a team of researchers headed by Jean-Jacques Hublin published a pair of papers describing a new set of fossils excavated from Jebel Irhoud, Morocco. The authors argue that these new discoveries are the earliest known Homo sapiens found anywhere in the world. This leads naturally to two simple questions: was this individual a human, and did it really live roughly 315,000 years ago?

To answer the first question, Hublin et al. used digitized 3D landmarks (or, a consistent set of points on all of the skulls) to statistically analyze the shape of the Jebel Irhoud specimens and compare them to a set of other hominin fossils. This allows you to compare shape differences independent of size differences. This analysis suggests that these specimens are more similar to Homo sapiens than any other species. That being said, this method is far from conclusive. Several of the major features that we use to identify Homo sapiens in the fossil record, including a vertical forehead, globular braincase, and protruding chin, are absent from the Moroccan fossils. Are these Homo sapiens because they are more similar to us than anything else, or do we need to rely on the presence of those specific traits to define the species? If they are humans, then we need to update our definition of what it means to be a human, morphologically. Even if not, it’s clearly something extremely human-like living in a time and place where we never expected to find one.

The second question has its own set of complications. The team (Richter et al.) used thermoluminescence dating of artifacts and electron spin resonance (ESR) dating of teeth to arrive at the date of the fossils. Thermoluminescence and ESR dating both measure radiation exposure (or accumulated dose) to determine the age of an artifact or fossil. The ESR dating suggested a date of 252 – 318 ka, but with a p-value that was not low enough to be statistically significant. In and of itself, that would be a tenuous basis for such an extraordinary claim, but the thermoluminescence dating of burned artifacts found in association with those fossils revealed a date of roughly 315 ka for the geological layer as a whole. This was repeated many times over. It’s not perfect, but the date seems reasonably secure.

What does this all mean? Why has this been reported everywhere, from social media to TV news? Most of the coverage has focused on the date. These may be the earliest members of our species ever discovered. That’s cool, and especially since it pushed back the first appearance date so far, from ~200,000 to ~315,000 years ago. But I think that misses the most interesting aspect of this discovery. It makes us reconsider what it means to be human in an evolutionary sense.

As the authors note in the title of their article, this find makes the case for a pan-African evolution of Homo sapiens. Whatever these individuals were, they were different from us, that much is clear, but they were more similar than anything else we’ve found outside of Homo sapiens. Did the traits that we use to define ourselves evolve piecemeal, across Africa? The discoverers of these new fossils suggest as much, arguing that the clear delineations between archaic and modern Homo sapiens no longer apply. It might be that these specimens represent a bridge between those two groups. If so, what we call them is largely a question of what definition you like to use for a species. That’s a question for another time, and maybe one that’s best to answer by looking at other species, where the stakes don’t seem so high.

One way you could characterize the last several decades of research in human evolution is to say that our understanding has changed from a linear evolution to a bushy one. We’ve filled out the tree a little more, and we see more of the branches and evolutionary dead-ends in our lineage. These finds are doing the same thing, but for the evolution of our own species, regardless of what they’re called. Hopefully this will inspire a new set of excavations across Africa, looking for more fossils to confound us and upend our expectations.

References
Hublin, J. J., Ben-Ncer, A., Bailey, S. E., Freidline, S. E., Neubauer, S., Skinner, M. M., Bergmann, I., Le Cabec, A., Benazzi, S., Harvati, K. & Gunz, P. (2017). New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature, 546(7657), 289-292.

Richter, D., Grün, R., Joannes-Boyau, R., Steele, T.E., Amani, F., Rué, M., Fernandes, P., Raynal, J.P., Geraads, D., Ben-Ncer, A. & Hublin, J.J. (2017). The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age. Nature, 546(7657), 293-296.

Rene Studer-Halbach is a PhD candidate in the Department of Anthropology at Rutgers University. He works on ecological niche modeling and community structure in South African Plio-Pleistocene primates.  

Academic Family Trees

You may have noticed from literally all of the preceding posts that evolutionary anthropologists are into family trees. Who is related to what and how? Is Homo naledi the weird cousin at the family reunion or your great-great-great-great-grandhominin? The interest doesn’t stop at the relationships between fossil taxa; anthropologists are also into their own family trees – their academic family trees, that is.

A couple of years ago, some anthropologists from the University of Texas started the Academic Phylogeny of Physical Anthropology (physanthphylogeny.org) with the goal of tracing advisor-advisee relationships in our field. The tree now includes 2036 people (including me!) from 163 institutions and goes back to some of anthropology’s biggest names, like Louis Leakey, Earnest Hooton, and Franz Boas, to name a few. (Hooton has the most descendants, by far.)

But some of the folks on the tree also have some more unusual “ancestors” – people who weren’t anthropologists at all (like Nobel Prize winning biologist Nikolaas Tinbergen). I’m one of those people; my earliest ancestor to make it onto the tree is Dr. Glenn Jepsen, the first person to be appointed Sinclair Professor of Vertebrate Paleontology at Princeton University. He also served as the Curator of Vertebrate Paleontology and the Director of Princeton’s natural history museum. He worked on Paleocene/Eocene fossil mammals from South Dakota and Wyoming, including preparing and describing the earliest known definitive fossil bat Icaronycteris index.

icaronycteris index
Icaronycteris index Jepsen, 1966 – From the Yale Peabody Museum of Natural History Collections website

That is one good-looking fossil bat. Anyway, what got me started writing this post is that, when I’m not shouting into the internet science void, I work as a collections technician at the New Jersey State Museum under the Curator of Natural History – who actually knew Jepsen! As Jepsen ran Princeton’s (now defunct) natural history museum and it was right down the road from the NJSM, there was naturally communication back and forth between Jepsen and various museum-affiliated people, some of which is still stored at the NJSM. Earlier this week, I found this amusing letter to him in a drawer of old correspondence:

Jepsen letter snip

“…and even the physical anthropologists,” indeed! Apparently we’re a tough crowd. Guess some things don’t change!

Thanks for reading! (And definitely check out physanthphylogeny.org)