#AAPA2017 – Modularity & evolution of the human canine

I’m recently returned from this year’s AAPA Conference, hosted by Tulane University in New Orleans. What a trip!

Usually my presentations involve fossils and/or growth, but this year I wanted to try a different way of looking at the evolution & development – integration & modularity. In short, biological structures that share a common developmental background and/or function may comprise ‘modules’ that are highly ‘integrated’ with one another, but relatively less integrated with other structures or modules.

I hypothesized that canine reduction in hominins is a result of a shift in modularity of the dentition, such that the canine became more highly integrated with the incisors than with the premolars. I’d thought of this 5 years ago when creating the first rendition of my human evo-devo course (offering again next fall!), but never got to look into it. Interestingly, the results generally supported my predictions, except for one pesky sample…

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As my primatologist friends will tell you, male chimps are the worst.

Here’s a pdf version of the poster. It was fun to dabble with a new methodology, to see my far-flung friends, and to visit a fun historic place for the AAPA conference. Definitely looking forward to next year in Austin!

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Worst year in review

As we’re wrapping up what may be the worst year in recent global memory, especially geopolitically, let’s take a moment to review some more positive things that came up at Lawnchair in 2016.

Headed home

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Alternate subtitle: Go West
This was a quiet year on the blog, with only 18 posts compared with the roughly thirty per year in 2014-2015. The major reason for the silence was that I moved from Kazakhstan back to the US to join the Anthropology Department at Vassar College in New York. With all the movement there was  less time to blog. Much of the second half of 2016 was spent setting up the Biological Anthropology Lab at Vassar, which will focus on “virtual” anthropology, including 3D surface scanning…

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Cast of early Homo cranium KNM-ER 1470 and 3D surface scan made in the lab using an Artec Spider.

… and 3D printing.

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gibbon endocast, created from a CT scan using Avizo software and printed on a Zortrax M200.

This first semester stateside I reworked my ‘Intro to Bio Anthro’ and ‘Race’ courses, which I think went pretty well being presented to an American audience for the first time. The latter class examines human biological variation, situating empirical observations in modern and historical social contexts. This is an especially important class today as 2016 saw a rise in nationalist and racist movements across the globe. Just yesterday Sarah Zhang published an essay in The Atlantic titled, “Will the Alt-right peddle a new kind of racist genetics?” It’s a great read, and I’m pleased to say that in the Race class this semester, we addressed all of the various social and scientific issues that came up in that piece. Admittedly though, I’m dismayed that this scary question has to be raised at this point in time, but it’s important for scholars to address and publicize given our society’s tragically short and selective memory.

So the first semester went well, and next semester I’ll be teaching a seminar focused on Homo naledi and a mid-level course on the prehistory of Central Asia. The Homo naledi class will be lots of fun, as we’ll used 3D printouts of H. naledi and other hominin species to address questions in human evolution. The Central Asia class will be good prep for when I return to Kazakhstan next summer to continue the hunt for human fossils in the country.

Osteology is still everywhere

A recurring segment over the years has been “Osteology Everywhere,” in which I recount how something I’ve seen out and about reminds me of a certain bone or fossil. Five of the blog 18 posts this year were OAs, and four of these were fossiliferous: I saw …

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Anatomy terminology hidden in 3D block letters,

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Hominin canines in Kazakhstani baursaki cakes,

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The Ardipithecus ramidus ilium in Almaty,

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Homo naledi juvenile femur head in nutmeg,

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And a Homo erectus cranium on a Bangkok sidewalk. As I’m teaching a fossil-focused seminar next semester, OA will probably become increasingly about fossils, and I’ll probably get my students involved in the fun as well.

New discoveries and enduring questions

The most-read post on the blog this year was about the recovery of the oldest human Nuclear DNA, from the 450,000 year old Sima de los Huesos fossils. My 2013 prediction that nuclear DNA would conflict with mtDNA by showing these hominins to be closer to Neandertals than Denisovans was shown to be correct.

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These results are significant in part because they demonstrate one way that new insights can be gained from fossils that have been known for years. But more intriguingly, the ability of researchers to extract DNA from exceedingly old fossils suggests that this is only the tip of the iceberg.

The other major discoveries I covered this year were the capuchin monkeys who made stone tools and the possibility that living humans and extinct Neandertals share a common pattern of brain development.

Pride & Predator

An unrelated image from 2016 that makes me laugh.

The comparison between monkey-made and anthropogenic stone tools drives home the now dated fact that humans aren’t the only rock-modifiers. But the significance for the evolution of human tool use is less clear cut – what are the parallels (if any) in the motivation and modification of rocks between hominins and capuchins, who haven’t shared a common ancestor for tens of millions of years? I’m sure we’ll hear more on that in the coming years.

In the case of whether Neandertal brain development is like that of humans, I pointed out that new study’s results differ from previous research probably because of differences samples and methods. The only way to reconcile this issue is for the two teams of researchers, one based in Zurich and the other in Leipzig, to come together or for a third party to try their hand at the analysis. Maybe we’ll see this in 2017, maybe not.

There were other cool things in 2016 that I just didn’t get around to writing about, such as the publication of new Laetoli footprints with accompanying free 3D scans, new papers on Homo naledi that are in press in the Journal of Human Evolution, and new analysis of old Lucy (Australopithecus afarensis) fossils suggesting that she spent a lifetime climbing trees but may have sucked at it. But here’s hoping that 2017 tops 2016, on the blog, in the fossil record, and basically on Earth in general.

Osteology Everywhere: Cakes or canines?

I’ve been looking at so many teeth lately, I’m starting to feel like a sadist but with newer magazines.

Between putting together a talk about dental development in Homo naledi and teaching teeth in my human evo-devo class last week . . .

After these drawings, my students were fully trained and ready to tackle the odontological world.

After these drawings, my students are now fully trained and ready to tackle the odontological world.

. . . I’ve got dentition on the brain. WHICH IS NOT THEIR ANATOMICAL POSITION.

So last weekend some friends and I hit a local pub,  a life jacket for my dental inundation. Surely, a pint and a snack will expunge enamel, dissolve dentine, exhume zuby from my brain! We ordered some beer and baursaki, delicious fried bread made out here in Kazakhstan, the perfect snack to go with beer and chechil. Tearing into the pastry, I started to feel at peace, but then was horrified to look down and find myself hoist with my own petard:

Baursak or bite?

Baursak with a bite taken out? Our a hominin canine?

Seeing the snack, I saw the very thing I’d been fleeing – a hominin canine tooth. Inadvertently, I’d almost exactly replicated Sts 50, a lower left canine crown and broken root from the South African site of Sterkfontein.

Left: Sts 50, lower left canine. Right: bitten fried bread. Images not to scale.

Left: Sts 50, lower left canine. Right: bitten fried bread. Images not to scale. ANTIMERES?

They’re nearly identical but from opposite sides (the fancy word for which is “antimeres”). Note the tall-shouldered, sharp apex of the crown, and the little distal tubercle, the little ‘bump’ at the far left in the left picture above. The mesial, or front, crown shoulder is notably taller than the distal tubercle. At probably around 3 million years ago, Sts 50 likely belongs to Australopithecus africanus, and retains an ape-like asymmetrical crown shape compared to the more incisor-shaped canines we humans have today.

Left to right: Homo baursaki, three South African canines, and a modern human (from White et al. 2012). Images not to scale.

Hominin canines and definitely no cakes. Left to right: Homo baursaki, three canines from early Pleistocene South Africa, and a modern human (from White et al. 2011). Images not to scale. Note how much less asymmetrical the modern human canine crown (far right) is compared to the fossil hominins. Teeth 1, 2, 4, and 5 are from the right side while the center, Sts 50, is from the left.

 

Apparently all you need to go back in time is some beer and baursaki.

What big teeth you have, indeed

If our friend Little Red Riding Hood was dumb enough to’ve thought a wolf in babushka threads was her grandma, well, she probably would have played Bingo with a grandmother-mimicking Australopithecus anamensis.
Australopithecus anamensis is the earliest undisputed hominid, found in deposits ranging from 4.2 – 3.9 million years ago in Ethiopia and Kenya (Leakey et al. 1995, White et al. 2006). Now, hominids are allegedly distinguished from other apes by having relatively short canine teeth distinguished by having relatively tall ‘shoulders,’ creating a diamond-shape in front view. Nevertheless, compared with humans these early australopiths had pretty murdersome canines, within the range of female chimpanzee species. (my dictionary is trying to tell me ‘murdersome’ isn’t a word, but I learned long ago not to learn right and wrong from a book)
Such canine form – relatively small with tall shoulders – was important in diagnosing Ardipithecus ramidus (> 4.4 million years) as a hominid back in the roaring 1990s (White et al. 1994). Of course, we learned in the 1980s that many ancient fossil apes looked superficially like hominids because of dental similarities, the result of either parallel evolution or hominids’ retention of primitive features. Indeed, even in light of the recently described Ardipithecus ramidus skull and skeleton, the main similarities with later, undisputed hominids are dental.
With this in mind, I’m struck by the canine of Nakalipithecus nakayamai, an ape from Kenya dating to nearly 10 million years ago (Kunimatsu et al. 2007). This is ape was a pretty important discovery because it began to fill in a rather lonesome Late Miocene ape fossil record in Africa. So, below is a picture of Nakali and anamensis canines, which I’ve tried to properly scale with the cutting-edge techniques of Microsoft Powerpoint (that is absolutely not a plug for Microsoft). On the left is Nakalipithecus, and the 2 on the right are Au. anamensis. The middle one is anamensis from Asa Issie in Ethiopia, and is the largest canine found of any hominid, ever I think. On the right is anamensis from Kanapoi in Kenya, not as big but sharp as shi…
…sh kabob skewers. Well crap, the “hominid feature” of short canine crown with nice shoulders is found in this 10 million year-old ape!
Two mutually exclusive scenarios could explain this similarity: [1] this canine morphology truly is a shared-derived feature of hominids, but hominids and Nakalipithecus just happened to evolve the same morphology independently for no better reason than, say, ennui. [2] This morphology is the ancestral condition for hominids (and chimpanzees and possibly gorillas). The fanciest cladistic methods won’t resolve this issue, only the discover of more badass fossils will. But if [2] is correct, that would deal a tough blow to the case of Ar. ramidus (and Sahelanthropus) behing a hominid. Really, it seems like the distinguishing feature of early hominids was their deplorable lack of distinguishing features.
ResearchBlogging.org
Oy, if bones and teeth are prone to homoplasy (similarity due to parallel evolution and not because of common ancestry), could paleoanthropologists have a special proclivity for it, too (that is, in naming dental hominids)?


Further reading!
Kunimatsu, Y., Nakatsukasa, M., Sawada, Y., Sakai, T., Hyodo, M., Hyodo, H., Itaya, T., Nakaya, H., Saegusa, H., Mazurier, A., Saneyoshi, M., Tsujikawa, H., Yamamoto, A., & Mbua, E. (2007). A new Late Miocene great ape from Kenya and its implications for the origins of African great apes and humans Proceedings of the National Academy of Sciences, 104 (49), 19220-19225 DOI: 10.1073/pnas.0706190104
Leakey, M., Feibel, C., McDougall, I., & Walker, A. (1995). New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya Nature, 376 (6541), 565-571 DOI: 10.1038/376565a0
Ward, C. (2001). Morphology of Australopithecus anamensis from Kanapoi and Allia Bay, Kenya Journal of Human Evolution, 41 (4), 255-368 DOI: 10.1006/jhev.2001.0507
White, T., Suwa, G., & Asfaw, B. (1994). Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia Nature, 371 (6495), 306-312 DOI: 10.1038/371306a0
White, T., WoldeGabriel, G., Asfaw, B., Ambrose, S., Beyene, Y., Bernor, R., Boisserie, J., Currie, B., Gilbert, H., Haile-Selassie, Y., Hart, W., Hlusko, L., Howell, F., Kono, R., Lehmann, T., Louchart, A., Lovejoy, C., Renne, P., Saegusa, H., Vrba, E., Wesselman, H., & Suwa, G. (2006). Asa Issie, Aramis and the origin of Australopithecus Nature, 440 (7086), 883-889 DOI: 10.1038/nature04629