You guessed it, we had another guest speaker this Friday instead of our regularly scheduled BS&M meeting. No complaints here, though. This week’s speaker is a giant in the field of paleoanthropology: Dr. Bernard Wood of the Center for the Advanced Study of Human Paleobiology at George Washington University. Dr. Wood stopped by Rutgers to give us his thoughts on the last ~50 years worth of work on the origins of the genus Homo.
Instead of just writing a summary of his talk, I’m trying my hand at Storifying my tweets from the event. Check out the thread and let me know what you think about this format!
Next week, alas, still no BS&M (!), but check back here for ANOTHER defense update! Stan Kivai will be defending his dissertation on the effects of mechanical and nutritional properties on foraging in juvenile Tana River mangabeys. Fingers crossed that the snake is small!
This week’s BS&M blog takes on two new pieces of anthro news – neither of which we’ve actually had a journal club meeting about!
The first bit of news has been making waves all over the internet (as news tends to do, I guess): a third species of orangutan has been named! The newly designated Pongo tapanuliensis, or the Tapanuli orangutan, comes from the southernmost extent of the previously known Sumatran orangutan (Pongo abelii) range. P. tapanuliensis was named on the basis of morphological and genetic comparisons, which suggested that its skeleton looks subtly different from that of all other living orangutans (for example, in having relative broad upper canines and a relatively shallow face) and that it’s the oldest orangutan lineage (having split from the line leading to the other two species around 3.38 million years ago). Pretty cool!
While the naming of a “new” mammal species (especially one as large as an orangutan) is always exciting, there are a few potential issues to consider. First,P. tapanuliensis was named on the basis of a single (male) specimen and two genomes. It’s possible that there are other Tapanuli orangutan skeletons in museum collections that were not previously recognized as different from the northern Sumatran populations; this would be a something to look into, in the interest of increasing sample size. I’m also curious about what the skeleton of a female Tapanuli orangutan might look like. Second, Nater et al. estimate that there are already fewer than 800 Tapanuli individuals left. This (and splitting the Sumatran orangutans into two species) has implications for conservation. Is it worth it to prioritize saving the more endangered Tapanuli orangutan, which may already lack a population of viable size, or is it better to concentrate efforts on the Sumatran orangutan? A more optimistic view might be that this new species will attract attention (and money, which is ultimately what allows conservation efforts to happen) to the plight of orangutans generally. It’s impossible to know. Either way, the “discovery” of the Tapanuli orangutan expands our understanding of the diversity of our closest relatives – again, pretty cool!
The second bit of anthro news is also about expanding our understanding of diversity, but this time of our own genome.
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!
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.
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 Homosapiens 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.
This past Friday, our journal club took on “The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters” (Argue et al. 2017). Essentially, Argue and colleagues attempted to figure out what other hominin species H. floresiensis (often called the Hobbit) was most closely related to, using statistical tree-building methods.
Since it was published in 2004 by Brown et al., H. floresiensis has been a bit of a mystery. Much like Homo naledi, there’s been a lot of discussion about where it belongs in the human family tree because its anatomy was A) weird and B) totally unexpected for its age (somewhere between 100-60 thousand years old) and its geographic location (on Flores, a small Indonesian island). The Hobbit was very short in stature, with a very small brain (in the range of orangutans, chimpanzees, and the much-older australopithecines), large teeth for its size, primitive-looking wrist bones, and disproportionately large feet relative to its height and leg length (hence its nickname of the Hobbit). Its discovery on Flores was a surprise because the other hominins that have been found in Indonesia (like Homo erectus from Java) were older and had larger brains (and we generally think brain size in the human lineage has increased over time – but last week’s chat about H. naledi also brought this up as a problematic assumption).
In their new article, Argue et al. set out to test two hypotheses: either the Hobbit is a late survivor from an earlier primitive hominin lineage, or it is a dwarfed descendent of H. erectus. They also commented on another controversial claim that’s been made about the Hobbit – that it is simply a modern human with a genetic/developmental pathology. They tested their hypotheses by applying two tree-building methods to a large sample of characters (particular features or measurements of the skeleton) from the skull, teeth, and postcranial (below the head) skeleton. One method (parsimony) attempts to build the shortest possible tree (one that requires the fewest changes in traits to get from species to species), while the other method uses probability to figure out which trees are most likely to occur (given a particular model of evolution).
When you set out to do a project like this, you’re forced to make some choices as a paleoanthropologist. If you have isolated postcranial bones from a hominin site where you’ve previously found fossils of more than one hominin species from the same time, how do you decide which body belongs with which head? You also confront the issue that not all researchers agree on which specimens belong in which species. And, as always, the fossil record is incomplete; you don’t have all of the characters for all of the species. To account for these potential problems, Argue et al. tested their two hypotheses with several different data sets – for example, they did one test where they considered all of the potential postcranial skeletal material that’s been called Homo habilis to actually be H. habilis and another where they excluded the questionable material.
What Argue et al. found was that their two different hypothesis testing methods and various different data sets produced broadly similar results in support of the first hypothesis: the Hobbit either shared a common ancestor with Homo habilis or is the sister group to the grouping of Homo habilis/Homo erectus/Homo ergaster/Homo sapiens. They are able to reject the hypothesis that the Hobbit is a dwarfed H. erectus (and reject a number of other species as possible close relatives). What this suggests is that (as was proposed for Homo naledi in last week’s papers) there is a long ghost lineage (unknown ancestors) for the Hobbit dating back more than 1.75 million years that is still waiting to be found. Ghost lineages – so hot right now.
On May 9th, Lee Berger and colleagues published three new papers on Homo naledi, the most recent South African hominin fossil find to make media waves. The original H. naledi fossil material was discovered in 2013 by two cavers working with Berger; it comes from the Dinaledi Chamber of the Rising Star cave system, from which it takes its species name (Berger et al. 2015). The first H. naledi discovery was remarkable because there are at least 15 individuals (from juveniles to adults of both sexes) represented in the assemblage and there are often multiple copies of each skeletal element present, which allows paleoanthropologists to look at variation within the species, and to see how it grew and developed. In total, there are about 1550 hominin bones and teeth in the assemblage – the largest single species assemblage found anywhere in Africa (Berger et al. 2015).
The three new articles covered the discovery of additional skeletal material (Hawks et al. 2017) and the age of the fossils (which had been a major source of speculation) (Dirks et al. 2017), and proposed a hypothesis for understanding Pleistocene hominin diversity in subequatorial Africa as part of a larger mammalian biogeographic pattern (Berger et al. 2017).
The new fossil material comes from a second chamber within the Rising Star system, the Lesedi Chamber, and represents at least three individuals (though in actuality the material likely comes from more than three individuals, based on where the bones were recovered from within the Chamber). The most spectacular of these remains is a relatively complete skull with associated skeletal material; the researchers have named this individual Neo. The new material looks a lot like the previously discovered H. naledi bones and teeth, and also includes both adult and juvenile material. The major thing that differentiates the Lesedi Chamber finds from the Dinaledi Chamber finds is that the Lesedi Chamber also contains animal skeletal material (Hawks et al. 2017).
The paper on the age of the fossils used several different methods (including dating geological features of the cave itself as well as directly dating some of the fossil teeth) to produce an age range for the material of 236,000-335,000 years old (Dirks et al. 2017). This means that the material is later Middle Pleistocene in age, much younger than would have been predicted based on looking at features of the skull and skeleton (like brain size).
In a previous paper, Hawks and Berger (2016) discussed what three different hypothesized ages (including a scenario that does match the new date) for the original H. naledi material would mean for its place in human evolution, and they follow up on this in the third new paper – now that we have a date, what does it mean? The date is younger than the first appearance of Homo erectus around 1.8 million years ago. As H. erectus is generally thought to be part of the lineage that is directly ancestral to us, this would seem to preclude H. naledi as a member of our direct line, unless it represents a sister group to our species that preserves a lot of the primitive morphology of a shared ancestor. This interpretation bumps H. erectus to a side branch of our family tree. A different type of analysis of the features of various species of Homo suggests instead a more bushy view of earliest Homo – whatever that ancestor was split into a number of species, each having only some of the ancestor’s features. What we can say is that H. naledi is likely only part of a branch that originated earlier in time, with the authors going so far as to suggest that we might already have fossils from earlier on this branch that we have not recognized due to their fragmentary nature (Berger et al. 2017).
Regardless of where Homo naledi ends up on our family tree, it’s still an incredible discovery that contributes to our understanding of the human fossil record. It provides a window into a time period in our history from which we don’t have great data and underscores two important ideas: first, that for most of our evolutionary history, Homo sapiens was not the only hominin species on the planet; and second, that there are still spectacular fossils waiting to be discovered.