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!

3 thoughts on “We’ll, I’ll be a Monkey’s Uncle. Or an Orangutan’s.

  1. Todd can continue to asserting his faith in DNA sequence matches as the final proof of evolutionary relationships, but it is only a faith based system that assumes that DNA matches, usually created through various statistical procedures, is the final word. Such beliefs, no matter how widely held, have not demonstrated any such thing. In failing to do so it creates an absurd situation where a plentitude of derived biological similarities shared between humans and orangutans has to be ingored as phylogenetically meaningless (i.e. accidents of convergence etc) and the fact that the early hominids looked more like orangutans than chimps.

    The last word on this issue has yet to unfold.

    John Grehan

  2. John-If you are correct and orangutans are more closely related to humans than chimpanzees are, then how do you explain away the genetic data?

    Under your model, the genetic data would then have to be ignored as 1 million convergent characters.

  3. To anonymous,

    The answer lies in systematics and the arguement is outlined in the orangutan publications. Basically it comes down to distinguishing between smilarity and relationship. There is a widespread assumption that similarity demonstrates relationship, but cladistics has shown this to be incorrect, and that only uniquely shared similarities provide evidence of relationship.

    The problem with the ‘genetic’ (its only genetci in the sense of using DNA bases)evidence is that it uses simialrity as proof of relationship. The methods sometimes use cladistic techniques and terminology, but the method requires constructing trees based on similarity and then the matches on the best tree are then defined as uniquely shared.

    So one does not ‘ingore’ the genetic data, but one just recongizes that the bulk of DNA similarities are likely to be primitive retentions just as this is the case for the bulk of morphological similarities by which we are more similar overall to African apes than the orangutan, even though it is the latter to which we are more similar in uniquely derived morphology, physiology, and behavior (28 and counting).

    John Grehan

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