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):
An in-press paper, available in the Proceedings of the Geologists’ Association on Aug. 31, describes trackways dating to 5.7 mya on Crete (shown in this post’s lead image, from Gierlinski et al. ). This places them just before the Messinian Salinity Crisis, when the Mediterranean dried up, global climates were nice and warm, and the planet really did belong to the apes. A potential hominin trackway (let’s be real, any trackway at all) from this time period is WAY COOL for a couple of reasons:
1. Tracks do not preserve very well. Ever go walking along the beach and look behind you to see your footprints washed away by the next wave? Yeah, me too. Most footprints made in the dirt, sand, or mud, are going to be washed away or destroyed by other individuals, or simply smoothed over because there is so much water in the sediment. For tracks to preserve, they have to dry out a bit, and then be covered pretty quickly by sediment that is a little different in texture or that won’t end up squishing together with the underlying layer. So tracks at all are always really cool, and offer a glimpse into environments and animal communities that we generally don’t see.
2. The Miocene gets called the Planet of the Apes because of the intense radiation of apes that happened during that time period (23-5.3 mya). We know some about the vast array of species that must have occupied the Old World at that time, but there is a lot we don’t know (again, see how to become a fossil), and what we don’t know may have been living on ancient Crete and walking, at least some of the time. Suspensory locomotion evolved sometime during this period (see Pierolapithecus, Dendropithecus, and Dryopithecus), and many later Miocene apes were highly orthograde (which just means they sat upright). Today, suspensory locomotors include gibbons and orangutans, and these (also orthograde) apes are able to walk on two legs over the ground, so it isn’t outside the realm of possibility that a highly orthograde ape had to move across a relatively open, albeit somewhat gooey, landscape and did so on two legs.
3. Footprints can tell us a lot about who made them, even if they can’t tell us definitively who made them. Footprints can give us clues about how many toes, or digits, are on a foot, whether the toes had nails, hooves, or claws, and the overall shape of the foot. We can determine the direction individuals were walking, and get a general idea of a minimum number of individuals within a group (to an extent –preserved footprints should represent individuals who are walking over the landscape at roughly the same time, but who can say if they were there together). In this case, the authors claim that the footprints show a foot that resembles ours with all the toes, even the big toe, together, but without claws or a defined arch. Because of this, the authors claim that an original (basal) member of the Hominini clade (our own branch of the family tree) made these tracks, and suggest that whatever it was eventually gave rise to whatever we are now.
I’m not convinced, but I am certainly intrigued. At 5.7 mya, it post-dates early potential basal members of our lineage (Sahelanthropus and Orrorin) residing in Central and Eastern Africa, where current evidence overwhelmingly supports hominin evolution in savannah environments. Crete is a long way from any of these places, even if the Mediterranean Sea wasn’t a factor, and there are no Miocene ape fossils found particularly close to the trackways site. That doesn’t mean these footprints don’t belong to Miocene apes, but it makes it harder to argue that it was definitely an ape and not, say, a bear. Especially given the vast array of apes inhabiting the Planet of the Apes, I don’t have a problem with the possibility that more than one Miocene ape stood up to get across a flat surface, but it would be nice to point to a fossil close by in time and space and say, ‘Hey, it’s probably that guy!’.
Reference Gierliński, G.D., Niedźwiedzki, G., Lockley, M.G., Athanassiou, A., Fassoulas, C., Dubicka, Z., Boczarowski, A., Bennett, M.R. and Ahlberg, P.E. (2017). Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?. Proceedings of the Geologists’ Association.
Sarah Hlubik is a PhD candidate in the Department of Anthropology at Rutgers University. She works on early hominin control of fire at Koobi Fora, Kenya.
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.
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?
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:
And then there’s haplotype E:
Yes, still a poodle, but also kind of…out there and unexpected.
So this happened on last night’s episode of Jeopardy:
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!
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.