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The Great (Ape) Taxonomy Debate

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As an undergraduate studying primatology, I was always confused about great ape and human taxonomy. Were we great apes? Or were we hominids? Or were we both? What was the consensus and was there logical and scientific reasons for lumping or splitting? To be completely honest, I never really resolved this internal dilemma. In hindsight it seems ridiculous considering how much time I spent thinking about it.

However, as an evolutionary anthropologist I have been asked whether I consider humans to be great apes. I always confidently reply that we are. Upon reflection I think I have responded this way because of my early evolutionary science influences. In college I read a lot of Richard Dawkins and Jared Diamond. Both of these academics have popularized the notion that we are the “fifth ape” or the “third chimpanzee.” (Diamond, 1992; Dawkins, 2004). In fact, Wikipedia and modern taxonomic classification both support this claim:

“The [great apes] form a taxonomic family of primates, including four extant genera: chimpanzees and bonobos (Pan), gorillas (Gorilla), humans (Homo), and orangutans (Pongo).” (Wikipedia: Hominidae (Great Apes))

So it seems to be an open and shut case right? Why should I lose any sleep over this taxonomic grouping? Humans are great apes.

However, I don’t think it is this straightforward. Whether we are great apes (lumping) or aren’t great apes (splitting) doesn’t just affect research and theory, but it also affects how we conceptualize what it means to be human. So what is the scientific evidence and reason behind lumping us in with the great apes?

The main justification for grouping humans and great apes together is anatomical and morphological. We share the same ‘Y5’ pattern (five cusps or raised bumps arranged in a Y-shape), a rotating shoulder, no tail, posteriorly positioned scapula, fused caudal vertebrae, and a large and complex brain (Marks, 2009).

To me, the most important of these anatomical and morphological similarities is the “large and complex brain.” It is true that the great apes have larger brain to body size ratios than all other primates. And it is this large brain size that allows the great apes to accomplish incredible intellectual accomplishments both in the wild and in laboratory settings. However, the human brain is at least three times the size of any great ape brain. The human brain exploded in size with the birth of the genus Homo, approximately 2 million years ago. Most importantly, the human brain has enabled levels of communication and intelligence unparalleled in the history of life on Earth.

This is no trivial difference. So why do we group ourselves with species that are quite different from ourselves? I think there are two main reasons: a) a scientific tradition that emphasizes ancestry over emergence and b) an evolutionary past that has left us with no extant sister taxa.

Biological anthropologist Jonathan Marks has recently explored the first of these reasons in great detail (e.g., Marks, 2009; Marks 2012). Marks claims that by lumping our species in with great apes, researchers create a human evolutionary framework that begins by assuming we never really became human. It also implicitly rejects an important Darwinian theoretical approach by focusing on descent, as opposed to divergence (Marks, 2009).

British anthropologist Robin Dunbar agrees with this basic philosophy, and stated this clearly in a 2008 article titled Why Humans Aren’t Just Great Apes. Within this article Dunbar claims that humans are different from great apes in one critical respect: our imagination (Dunbar, 2008). I would contend that there are several more critical differences between the human mind and the great ape mind, but I do agree with Dunbar’s approach of stressing the ways in which humans are divergent from the great apes.

The classification of humans as great apes is also dependent on a historical contingency: we have no extant sister taxa. In the not-so-distant past humans shared this planet with several other humans. In fact, the last non-sapiens member of the Homo line suffered extinction approximately 13,000 years ago. This means that for over 90% of our species existence, we shared Earth with other humans. Despite this, none remain today (and it is probably our fault). If one or more of these other humans had survived into contemporary times, our taxonomic classification scheme for humans and great apes would undoubtedly look much different. Instead of focusing on the similarities between humans and chimpanzees, or humans and gorillas, we would likely shift our attention to focusing on the similarities between humans and … other species of humans.

It would be difficult for taxonomists to lump two or more human species in with the great apes. The differences would be far too striking.

The implications of splitting humans from great apes taxonomically would be beneficial. Conceptually it would allow researchers to better understand the hominid/ape divergence and the key differences between humans and great apes today. But perhaps more importantly, splitting humans from the great apes allows us to reconceptualize our own humanity. We are not the great apes; we are humans. The great apes are our closest extant relatives, and it is incredibly important to study, protect, and conserve them. However, we can’t use their title as closest extant relatives as a strategic rhetorical device to emphasize similarity.

References:

Dawkins, R. 2004. The Ancestor’s Tale. Boston: Houghton Mifflin.

Diamond, J. 1991. The Third Chimpanzee. Hutchinson Radius.

Dunbar, R. 2008. Why Humans Aren’t Just Great Apes. Ethnology and Anthropology, 3: 15-33.

Marks, J. 2009. Why I Am Not A Scientist. London: University of California Press.

Marks, J. 2012. Why Be Against Darwin? Creationism, Racism, and the Roots of Anthropology. Yearbook of Physical Anthropology, 55: 95-104.

Images: Man of the woods; Caucasian Human Skull

The views expressed are those of the author and are not necessarily those of Scientific American.

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