The latest on Homo naledi

Relatively complete skeletons from early human ancestors typically generate a ton of buzz in the popular media. None, however, has generated as much in the last 10 years as the finds of Homo naledi. The remains of at least 15 individuals have been unearthed within the Rising Star Cave System in South Africa since its discovery by cavers in 2013. In 2017, an additional three individuals were announced from a separate chamber in the cave. The finds show an interesting, and perplexing, mixture of traits that recall everything from Homo habilis to H. erectus and even Australopithecus.

Last fall, the President of our Student Anthropological Society here at UNCG, Cory Henderson (who was recently accepted to graduate school at Penn State), asked me if I could get in touch with a friend of mine, Dr. Zach Throckmorton, who is a member of the Rising Star team, to talk about Homo naledi. Zach generously agreed, and on Friday, April 7th the Department of Anthropology and Student Anthropological Society at UNCG hosted Zach and another Rising Star researcher, Dr. Chris Walker. The background to the Rising Star discovery and the rapid fire, open-access approach to research dissemination are well documented and controversial, and I'll leave it to the reader to delve into those issues. Here, I'll just summarize what I found to be particularly intriguing. First up was Zach, who is an expert on feet and discussed the post-cranial anatomy:

• H. naledi has long thumbs, just like modern humans (this is one of the features that gives us the ability to precisely manipulate objects with our hands). However, the fingers are somewhat curved.
• The torsion, or twisting, of the humeral shaft relative to the humeral head is odd in that it falls within a range of modern monkeys. 
• The lower limb, including the foot, appears to be more-or-less modern human-like. However, H. naledi was small--Zach estimates that the complete foot would have fit into a size 3 shoe. 
• So, overall, the upper limbs retain some features that may be adaptations for climbing, while the lower limbs share many similarities to modern humans. 

Chris followed with a discussion of growth and development in H. naledi:

• A majority (eight out of thirteen, to be exact) of the individuals from the cave for which age can be determined are juveniles. Most of the complete long bones are also from juveniles. 
• Based on the dental data, it seems that H. naledi followed a modern-human like growth trajectory. 
• The legs are very long relative to body size (which was pretty small, perhaps 147 cm and around 45 kg), but the intermembral index is human-like. This means that H. naledi had longer legs than would be expected for a hominin of its body size but they are not longer relative to their arm length than would be expected for a modern human. Such long legs may be an adaptation for efficient terrestrial bipedalism. 

The anatomy of H. naledi, and the provocative interpretation put forward by the Rising Star team for the assemblage's origin (the intentional disposal of the cadavers within the cave by other hominins), was even more puzzling because no one knew how old the fossils were. Based on their morphology, some estimated the fossils to be early Pleistocene in age (perhaps one or two million years old). A colleague who has seen the bones first hand told me that they didn't appear to be fossilized, which is difficult to accommodate with such an ancient date. Earlier this year the Rising Star team announced a much younger date of ~300,000 years. While deliberate placement of the bodies in the cave is perhaps more easily reconciled with a younger age, the brain size (less than half the size of a modern human) and the complexities of cave geology make this hypothesis far from demonstrated. Either way, this is extremely interesting, and I am looking forward to seeing where it goes...

Teaching human evolution to the public

I convinced my friend and colleague Briana Pobiner to come down to Greensboro from Washington, D.C. to present on her education and outreach work with the Smithsonian. Briana's major research interests focus on the evolution of the human diet, but recently she's become deeply involved in public outreach and the teaching of evolution, particularly human evolution. Her presentation "Communicating Human Evolution" drew a good crowd (including a couple of university donors) and outlined the efforts of the Human Origins Program at the Smithsonian to explain human evolution to the public. A couple of salient points/observations:

• Briana presented a bunch of data on public attitudes to science, scientists, evolution, and human evolution. Perhaps the most surprising number was 42. This is the percentage of Americans that do not accept organic evolution as an explanation for biological diversity. Even more troubling is the fact that this number has not really changed much since 1982! A sobering realization given how much time, effort, and money has been devoted to improving science education in the U.S. 
• One of the most important points that Briana made was that convincing people of the fact of evolution requires open dialogue−brow beating simply causes people to dig in their heels. One of the things that the Smithsonian is doing is to make their scientists available to the public. 
• The last thing that I found to be interesting was the reason why so many folks view science, and human evolution in particular, with such circumspection: when you see headlines announcing the latest find, it often reads something like "new fossil find overturns all previous models of human evolution." This sort of stuff garners readership, no doubt, but is also inaccurate. (If we're constantly overturning everything we know, it's no surprise that the public views the science behind it with some suspicion!) The fact is, even the most incredible find simply fills in the gaps of a well-established body of knowledge.

If you have not seen the National Museum of Natural History's human evolution exhibit (it opened in 2010), go visit! It is top-notch.

Ashby Dialogue, Part 1

So, this semester (Spring 2014), the Department of Anthropology at UNCG, along with the Departments of Biology and Interior Architecture, are organizing and hosting an Ashby Dialogue, which, through an endowment from the College of Arts and Sciences, "provide the opportunity for informal but focused inquiry into some topic or issue" of interest to university faculty and students. I helped a bit in the planning and organizing, but the lion's share of the work was done by our own Joel Gunn and biology's Malcolm Schug. Our theme for this semester is "Human Adaptation: Past and Future," and you can see the full schedule of events here. This is the first of several posts I'll provide throughout the semester as we progress through our program.

To kick off the schedule, we had hoped to have a talk from Greg Wray, a top-notch evolutionary biologist from Duke University who is interested in the evolution of gene regulation. Unfortunately, the winter storm (defined in North Carolina as a threat of snow or, in our case, an inch or so of snow) we had last week shut down campus and we had to cancel. Nevertheless, we did go forward with our first discussion session on Monday, February 3, and I'll recap that here.

The theme of our first session was How do Biologists Study the Question: What is the Evidence for Adaptation in Humans? There were a total of 10-11 people, including students from both anthropology and biology. We had posted a reading about next generation sequencing of genomes and two videos, one from Evan Eichler (Washington University) about structural variation in the human genome, and another from Sarah Tishkoff (University of Pennsylvania) about variation among modern African populations and evidence for the evolution of lactose tolerance, all of which served to focus our discussion.

We started off with an introduction from Malcolm, who gave us a great overview of the issue of genetic adaptation. He noted first that although "adaptation" can be viewed somewhat differently by anthropologists and biologists, Darwin's theory of natural selection and its focus on reproductive success serves to unite both fields. Biologists traditionally thought that because organisms appeared so well adapted to their environments that very little genetic variation would be present. This idea was blown apart by the work of Richard Lewontin and John Hubby, who in the 1960s documented a surprising amount of inter-individual variation in various proteins (this work was done first with flies and then, later, with humans). Further work by Martin Kreitman found tons of variation in DNA. All of this raised an important question: why the heck is there so much genetic variation between individuals if populations are supposedly well adapted to their environments?

Well, two answers emerged. One, which I'll dub the "adaptationist camp," thought that most of this variation was driven by natural selection (in this sense, inter-individual variation it is actually an adaptation in itself, since this variation will provide natural selection with something to work on). The issue then became to find the specific genes that were being selected for. The other side, which I'll call the "neutral camp," felt that most variation arises by random drift and alleles that have little or no effect on the survivorship of individuals. The debate was pretty acrimonious, but it seems like most folks recognize that both forces are probably at play.

To complicate matters further, Allan Wilson later suggested that perhaps it wasn't the genes themselves that were being selected for, but rather their regulation (i.e., when they are turned off and on, or how strongly they are expressed). Their is, for example, evidence that the human opposable thumb (the length of which permits us to manipulate small objects with ease) evolved not because of some structural change in a specific gene, but rather a change in when (and for how long) the genes responsible for the development of the hand were "turned on."

As Malcolm and our reading pointed out, the rapidly progressing genomic sequencing technology (it took years to sequence the first complete human genome about 15 years ago; we can now sequence entire genomes for everything from bacteria to human in DAYS) now permits huge amounts of data to be mined for evidence of natural selection. Now, geneticists can fish through whole genomes looking for gene that have undergone, or currently are undergoing, selection. I asked Malcolm how one goes about doing this, and he said that, essentially, geneticists scan the genomes of many individuals looking for allele frequencies that are higher (or lower) than expected (this can be determined statistically). I wonder if the technology is outpacing our ability to actually analyze it in a systematic way? Very interestingly, Malcolm told us about a study that simulated the evolution of a fruit fly genome and went back and identified "selected" genes with these statistical methods. Many were found, but the simulation did not include natural selection! So, it is by no means clear in every case whether or not genes have undergone natural selection.

Anyway, the clearest evidence for natural selection among most studies comes from genes identified with pathogen pressure and/or immune function and gametogenesis. Some other genes that appear to have been under selection over the course of human evolutionary history are FOXP2 (development of speech and language areas of the brain) and EDAR (development of several body tissues, including skin and sweat glands). We had additional conversations and discussions over pizza, including the issue of genetic determinism and how we define and analyze "traits."

Overall, a great start to our dialogues. I, along with Gwen Robbins Schug of Appalachian State, will be moderating our second session, which deals with past human adaptations to sedentism and urban life.