We’ll, I’ll be a Monkey’s Uncle. Or an Orangutan’s.

Our Guest blogger today is Dr. Todd Disotell, a professor of anthropology and a molecular primatologist at New York University’s Center for the Study of Human Origins. He will be speaking at HMNS on Feb. 9 at 6:30 p.m. about new molecular analytical techniques and how mapping whole genome sequences has affected what we know about the past. In his blog below, Dr. Disotell debates a recently proposed theory that humans are more closely related to orangutans than chimpanzees – a theory he disagrees with.

Posing for the Camera
Creative Commons License photo credit: jimbowen0306

This past summer upon the publication of a paper by a colleague, I found myself at the intersection of a 25 year old hypothesis, the latest research in genomics and bioinformatics, and popular culture.  Jeffrey Schwartz of the University of Pittsburgh and his coauthor, John Grehan of the Buffalo Museum of Science published an updated version of their hypothesis that orangutans are more closely related to humans than are chimpanzees in the Journal of Biogeography.  This intrigued me because in my final year of graduate school, my advisors and I published one of the earliest papers utilizing DNA sequence data supporting the growing consensus that chimpanzees were our closest relative, followed by gorillas, and much more distantly orangutans.

Perhaps due to my working in New York City, a producer from the Daily Show with Jon Stewart called me at my office and wanted to know if I was willing to be interviewed about Schwartz’s hypothesis.  As a fan I readily agreed and correspondent John Oliver was dispatched to my laboratory to interview me.  During the course of the interview in which I stated that the hypothesis flew in the face of all known genetic evidence, I opined that I would at least get to write a counter paper and perhaps a counter-counter paper if Schwartz responded.  That got me thinking about newly available genomic data that was now available in various databases which had not been fully analyzed.

Confused chimp
Creative Commons License photo credit:
Tambako the Jaguar

I then downloaded the complete genome alignments that included human, chimpanzee, gorilla, orangutan, macaque, marmoset, lemur, and galago.  After writing a series of Python scripts (an open source computer programming language) to parse and reformat the masses of sequence data, I chose the first 1 million bases of each chromosome for which all of the above species were represented.  I then used well characterized statistical and analytical techniques to infer the evolutionary history of each DNA region.  Not surprising to me, the analysis of each region convincingly rejects the hypothesis that orangutans are more closely related to humans than are chimpanzees.  Furthermore, when these 30 million DNA bases are used to estimate the time of divergence between humans, chimpanzees, and orangutans using molecular clock techniques, the orangutan appears to have diverged at over twice the age chimpanzees have from humans.

These results are not at all surprising to the absolute majority of paleoanthropologists and evolutionary primatologists.  However, it is still worthwhile to occasionally revisit theories and hypotheses that we now take for granted when new data are generated and new analytical techniques are developed.  In this genomic age, as the genomes of more and more species and even individuals within species are being sequenced, a whole new class and scale of analyses can be carried out from the keyboard.

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Check out Dr. Disotell’s lecture, “Times Are a-Changin’: New Methods Tell A New Tale of Primate Evolution” at HMNS on Feb. 9 – get tickets here!

Teeth Tell Tales

In an earlier blog, I discussed how experimental archaeologists can help us understand how ancient hominids manufactured stone tools. Astute readers might bring up these two facts:

• Stone tools date back to “only” 2.6 million years ago, and
• Currently, the earliest fossil hominids are dated back to 6, perhaps even 7 million years ago.

Can we ever hope to reconstruct the oldest hominids’ behavior, given that we do not have the benefit of associated artifacts?

The answer is yes. Our ability to reconstruct ancient hominid behavior predating the earliest know stone tools is more limited than that of the genus Homo, but it is possible nonetheless. How? The clues are in the bones and teeth.

Working like a forensic anthropologist:  paleoanthropologists can tell us about the age of individuals and their diet. Lucy is identified as an adult individual based on the presence of her wisdom teeth.

With regards to reconstructing ancient diet: the teeth of the species Paranthropus boisei were very large, set in immense jaws, with the lower jaw connected by massive muscles to a bony ridge on top of the skull. This configuration suggests the ability to crack open or chew through some very tough foods.

Given that Paranthropus existed for 900,000 years or more, the retention of these dental traits must imply that this dental characteristic served a purpose. As the thinking goes, if Paranthropus was eating primarily softer food items, like berries, then over time, its massive jaw architecture and very large teeth would have diminished in size.