New anthropology syllabi for 2017

This Fall I’m teaching three courses at Vassar, two in Anthropology and one in Environmental Studies. Syllabi are posted to my Teaching page in case anyone wants to use them – here are the highlights:

Anth 235: Central Asian Prehistory

Anth 235 site map

I taught this for the first time last Spring, so the Fall syllabus is updated based on how things went in the first go around. This time, students will get more more in depth with the fossil hominins and less on the lithics on the early side. On the more recent end, there are now readings expressly concerned with sites of the Bactrian-Margiana Archaeological Complex, as well as archaeology of both the Tarim and Pazyryk mummies.

Anth 305: Human Evolutionary Developmental Biology


This is a seminar version of the first class I ever made on my own, previously taught at the University of Michigan and Nazarbayev University. There have been lots of new discoveries and I’ve published more on this topic since the last time I taught the class. I’m  also excited to see how this class goes as a seminar in which students contribute more to discussion, rather than me rambling on about osteoblasts, morphological integration, and the like.

Enst 187: A Prehistoric Perspective on Climate Change


This is a 100% brand spankin new class, that uses the climate-denialist argument, “But climate has always been changing,” as a basis for comparing the past and the present. In this First-year Writing Seminar, we’ll compare arguments for defining the “Anthropocene,” examine how climate change may have impacted human evolution, and study archaeological evidence for how climate change has impacted different prehistoric societies.


Historical contingency and an herbivorous calamity

This post was chosen as an Editor's Selection for

A while ago I asked, “What the hell was Australopithecus boisei doing?” To recap: there’s this weird side branch of human evolution that was dubbed “Australopithecus boisei” and lived in Eastern Africa from around 2.3 – 1.4 million years ago. They lived right alongside our ancestors, early Homo. If you think human diversity is remarkable today, you’d be totally blown away by the diversity of the early Pleistocene. Since 1959 when A. boisei (then Zinjanthropus boisei) was first discovered, people noticed its massive molar and premolar teeth, thick and powerful jaws, and muscle markings indicative of diabolical chewing power. ‘Probably subsisted on a diet of low-quality, hard to chew foods,’ people reasoned.

But a few years ago, this picture changed: evidence from toothwear and the chemical composition of teeth suggested A. boisei was actually eating grass or sedges (see the referred post or a nice recent review by Julia Lee-Thorp for more info). Such a diet is totally at odds with what people had hypothesized based on the size of the chewing muscles and teeth.

Colobus molars, good for shearing apart leaves. (image:

I was discussing this last point with a colleague the other day, who could not believe A. boisei ate grasses or the like: Many animals known to eat grass or leaves tend have molars with high crowns with slicing edges for shearing apart a mouthful of vegetation (above), but A. boisei molars are large and low-cusped, becoming fairly flat with wear (below).

Australopithecus boisei specimen KNM-ER 15930 (Leakey & Walker 1988, Figure 8)
But, it occurred to me, maybe high-crowned, shearing molars simply were not an ‘option’ in the evolution of Australopithecus boisei. Natural selection is a powerful force of evolution, but it is limited because it can work only with existing variation: it does the best it can with what it’s got. The earliest surefire hominins, Australopithecus anamensis and afarensis, certainly did not have ‘cresty’ molars with pointy cusps, and neither did many late Miocene apes, for that matter. Rather, the ancestors of A. boisei had fairly low bulbous molar cusps, and that’s some serious evolutionary baggage for a hominid hoping to corner the grass and sedge market.
So we can draw up the following hypothesis for the evolution of A. boisei: as the early members of the species moved into a niche of eating grass/sedges, rather than evolve cresty teeth, they increased the size and enamel thickness of their ancestors’ molars to better-withstand their diet. Perhaps this was the ‘easiest’ solution to adapting teeth to a crappy diet (maybe some developmental constraint?). Or perhaps there’s another, yet unidentified food responsible for the species’ curiously high-C4 diet … who knows? Nota bene: this isn’t necessarily what I think happened, it’s just a hypothesis consistent with current evidence about A. boisei‘s anatomy and diet.
If Life on Earth has taught us anything, it’s that there are many ways to do the same thing. What’s more, evolution is highly constrained by pre-existing biology and historical circumstance. Australopithecus boisei may have been ‘a victim of its times,’ forced into an herbivorous niche for which it was ill-equipped.
Leakey RE, & Walker A (1988). New Australopithecus boisei specimens from east and west Lake Turkana, Kenya. American Journal of Physical Anthropology, 76 (1), 1-24 PMID: 3136654
Lee-Thorp, J. (2011). The demise of “Nutcracker Man” Proceedings of the National Academy of Sciences, 108 (23), 9319-9320 DOI: 10.1073/pnas.1105808108
*Edited 07 Nov 2015

Evolution: What it is and why humans aren’t immune to it

An alternate title for this post could be “BigThink Too Big For Own Britches.”

Physicist Michio Kaku (via John Hawks via Pharyngula) has re-brought my attention to the fact that a great deal of people who don’t study biology have no idea what evolution is or how it works (smart people like Kaku included). I will no further rebuke Kaku for abusing his power as a respected public figure in big Science and saying things that are outside his purview, not to mention just incorrect. His comments on biology would be like me telling high school students that the invention of the wheel or lubricants have obviated the effects of friction. Rather, I think it might be best to refresh people on what evolution is and how it works.

Quite simply, evolution is change in a gene pool. This pool could be an entire species or a small population within that species.
There are a number of ways evolution can happen. A mutation is a new genetic variant that arises in an individual, which can then be spread to later generations when that individual reproduces. A single strand of human DNA is like a string of some 3 billion letters. When a person replicates their DNA for it to be passed on to their offspring (meiosis), having to reproduce such a long strand ensures that a mistake is made at least once in a while. Hence mutations increase variation in a gene pool.
But the frequencies of genes in a population can change, that is they may become more or less common within the gene pool. This could happen by genetic drift, which is the random loss of genes. If a gene is neither adaptive nor harmful, it could simply be lost over time due to sheer chance. In contrast to mutation, drift reduces genetic variation.
If genes are adaptive or harmful, their frequency in a gene pool becomes subject to natural selection. If a gene (or set of genes) is adaptive, that means the possessor of those genes will be more likely to survive and reproduce than others. This advantage ensures the individual will pass on these genes. Over time, the adaptive genes will increase in frequency in a population. Conversely, genes that lower the likelihood of surviving and reproducing will be culled by selection. Either of these scenarios means selection is reducing genetic variation. But sometimes different forms of a gene can be adaptive in different situations or combinations, so selection will act to maintain both of these in the gene pool. So in contrast to mutation and drift, selection can reduce or maintain genetic variation.
Finally, gene flow refers to genes being introduced into a gene pool from another source. This could occur when someone from one population reproduces with an individual from another population, and so new genes may enter one of the groups. Like mutation, this will increase genetic variation in a gene pool.
Common misconceptions
It may seem counterintuitive, but evolution does not equate with progress. This is a common misconception, probably due to the social ideologies under which evolutionary theory developed. Because of selection, evolution often means that a population becomes better-suited to its environment over time, which seems like progress. But as we’ve seen above, not all evolution is selection; mutation and drift are fairly random processes of evolution that don’t necessarily bear on adaptation. In addition, environments and circumstances change, so that even if something evolved in a place where it was adaptive, it may be harmful in a new context. For example, as the earliest humans lost their body hair, they probably evolved to have darker skin: adaptive in the tropics where humans originated. But later, when early humans moved into more northerly latitudes with less ultraviolet exposure from the sun, the dark skin that was adaptive for a hairless human in a tropical environment came to hinder the body’s vitamin D synthesis: maladaptive!
Also contra popular opinion, individuals do not evolve, populations do. Trojan brand condoms recently had an ad campaign in which they encouraged men to “evolve” by using Trojan condoms when having promiscuous sex. This is in line with the incorrect idea above that ‘evolving’ means ‘becoming better’ or ‘more sophisticated.’ Of course, condoms may actually help a population to evolve: those who use condoms to prevent pregnancy are ensuring they do not pass on their genes. And if there’s any genetic predisposition to make one more likely to use condoms (and there’s not), these genes would certainly become less common in future generations. [I am NOT encouraging people not to use protection, by the way]
So this brings us to a final point: the outrageous thing (well, the main one) Dr. Kaku foolishly leashed upon an unsuspecting world is that humans are not evolving. Technology and urbanization, he tells us, has obviated natural selection on human features (well, the “gross” or visible ones). This is very wrong and shortsighted. In fact, this is one of the bases of the eugenics movement of the early 20th century. Eugenicists thought, ‘Nature is no longer ensuring some people don’t pass on their genes, so we ought to do it ourselves for the good of humankind.’ This first thought, about the insufficiency of Nature, is echoed by Dr. Kaku (surely he does not think the second).
Simply HUMANS ARE STILL EVOLVING. Remember, not all evolution = natural selection. The genetic composition of humankind is still subject to the random forces of mutation and drift. In fact, because the human population size has increased exponentially of late, the fact that there are way more people than ever means that there are more mutations entering the population, and at a faster rate, than ever! But selection is still at work, too. There are still diseases that kill people before they can pass on their genes. There are still environmental situations – even in civilized places! – that prevent people from passing on their genes.
We humans are still evolving because we are still subject to the forces of evolution, and we always will be. Now what physicist could’ve told you that?!