The Border Between Non-Human and Human: History and the Ledi-Geraru Jaw

Photo Courtesy William Kimbel

Ledi-Geraru Jaw, Photo Dr. Kimbel

When it comes to science, history matters. A scientific discipline’s history tells us how concepts were formed, how ideas have spread, and, in this case, how old debates can resurface with new fossils. In an article published last week, renowned anthropologist Jean-Jacques Hublin appealed to history to inform his discussion of the recently discovered Ledi-Geraru jaw.

In the article,titled “Paleoanthropology: How Old is the Oldest Human?”, Hublin reminds us that the genus Homo, has a contentious history. Homo, of course, is an important and personal genus as it indicates the beginning of our own family. Therefore, the earliest members of the genus Homo are often thought of as the first “humans” (in a loose sense, not in a strict Homo sapiens sense). And as the number of proposed species during early Homo increases (which it has), the question of which ones led to Homo sapiens becomes more difficult to answer.

OH-7

OH-7

But how do paleoanthropologists know what counts as Homo? At one point does a fossil look “human enough” to call it the first human? At 3.2 million years ago, Lucy had human features. At 1.5 million years ago, the Turkana Boy had many more human features, but where, in between, does the humanness line get drawn, and why? The issue has always centered around brain size, but the picture of the hominin landscape during the time period of early Homo is still quite fuzzy, fraught with debates about variation, sexual dimorphism, and other issues.

Its important to remember that the idea of a Homo genus is a invention of science. And this invention has had to be readjusted and reconfigured during the course of the history of paleoanthropology. Hublin recounts this history in his article, detailing the “redefinition” of the genus Homo that occurred when the Leakys described Homo habilis as a new species, based on the fossils known as OH7. The redefinition was about brain size, and it sparked a debate that Hublin argues has been one of the most intense in the history of paleoanthropology.

15000

Turkana boy, Homo erectus from Kenya

This debate asked scientists to expand the concept of Homo to include more creatures with smaller brain sizes. If Homo includes species with smaller brain size, then the border between the human genus and other hominin groups gets more blurry. Hence Hublin raising the question of the border between human and non human. Hublin has called upon this historical debate because he argues that the recently discovered Ledi-Geraru jaw re-opens the issues.

As I covered in a post a couple of months ago, the jaw dates back to 2.8 million years ago, much further back in time than scientists thought the genus Homo extended. The Ledi-Geraru jaw once again confronts scientists with the question “what should we call Homo?” The little jaw isn’t enough to tell scientists what they need to know about brain size and species diversity before answering that question, but hopefully more fossils will help settle the issue.

Hublin’s short article raises numerous interesting questions, but for me the main take away was that these issues of brain size and what should constitute the Homo genus have surfaced before in the history of paleoanthropology, and will continue to surface. As a historian, I greatly appreciate Hublin’s ability to contextualize the new jaw in deeply entrenched issues. Hublin concludes the article stating that “the border between non-human and human is not the sharp Adamic emergence that has long been favored, but is rather a long and fuzzy transition.” He also reminds us that “Africa still has many paleontological secrets to yield.”

Sources:

Hublin, Jean-Jacques, “Paleoanthropology: How Old Is the Oldest Human?” Current Biology, 25, June 1 2015.

Wood, Bernard, and Mark Collard. “The changing face of genus Homo.”Evolutionary Anthropology: Issues, News, and Reviews 8, no. 6 (1999): 195-207.

2 thoughts on “The Border Between Non-Human and Human: History and the Ledi-Geraru Jaw

  1. We are hopelessly mired in our own sense of importance. The two most commonly used lab strains of Drosophila melanogaster differ in sequence by 2% and we won’t put humans and chimps in the same genus.

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    • Yes, it seems to be difficult to apply concepts like diversity that we see in other parts of the biological world to our own history. Ian Tattersall has covered this idea of human exceptionalism in paleoanthropology quite well in some of his books, including his new book that I’m currently reading ‘The Strange Case of the Rickety Cossack.’

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