Did Humans Evolve On The Savanna? The Debate Heats Up

Enlarge this image Don Emmert/AFP/Getty Images Don Emmert/AFP/Getty Images

"Without original research or new data, Dominguez-Rodrigo attempts to resurrect 'the spirit of the old savanna hypothesis' via word games and revisionist history ... This attempted resurrection of an obsolete mind-set will stand as a monument to futility. — paleoanthropologist Tim White, in response to prehistorian M. Dominguez-Rodrigo's article on the savanna hypothesis of human evolution, in the February 2014 Current Anthropology.

"By denying [the] evidence [for the savanna hypothesis], White exemplifies perfectly Kuhn's idea that when a paradigm is assaulted, supporters of the old guard remain intentionally blind to the mounting evidence or selectively utilize data in order to resist change." — Dominguez-Rodrigo's reply to White's critique.

In a word, wow.

By the standards of discussion these days on blogs and discussion boards, this exchange may seem relatively mild. But it's acidic stuff for a peer-reviewed science article, even in the contested arena of human-evolution research. When I read Dominguez-Rodrigo's article and White's reply last week, I wondered, is this sort of exchange good for science?

I find journals like Current Anthropology and Behavioral and Brain Sciences both fun and informative because they publish, at the conclusion of their main articles, a set of response commentaries by experts on the topic. The immediate payoff of reading these multiple perspectives is an extra level of engagement and critical thinking on my part. I love it, too, when these exchanges get a little heated. Vigorous debate is a vital avenue toward deeper understanding of the issues, and may spur new hypothesis-testing.

But should there be some boundaries? Should we strive for the high road in terms of civility in peer-reviewed publications?

I say "yes" to both questions. To me, the printed Dominguez-Rodrigo and White exchange doesn't do science any favors. (The full exchange is much longer than the quotes that I selected from the article.)

Let's get into some specifics of the issue at hand. Dominguez-Rodrigo takes up a hypothesis familiar to many of us: Evolution of the human lineage was triggered when a primate population came down out of the trees and encountered new selection pressures on the savanna. Those pressures included a need to move greater distances across the more open landscape, a greater risk of predation and a harder time finding adequate food, and over time they selected, among other things, for walking upright — a hallmark in this context of the human lineage.

In recent years, the savanna hypothesis was challenged by the discovery in dense woodlands of certain hominins (human ancestors), early ones like Ardipithecus who lived in East Africa more than a million years before the australopithecine Lucy. Because these hominins were capable of bipedalism, it couldn't have been the savanna that was responsible for triggering our origins.

Dominguez-Rodrigo wants, however, to rescue a version of the savanna hypothesis. "The unambiguous structural definition" of a savanna, he writes, "is a landscape with a grassy cover, where trees are sparse enough to allow grass growth." A savanna is not inevitably synonymous with a pure grassland, but rather may be made up of a variety of open and wooded habitats. In his analysis, Ardipithecus and other early hominins dwelled in seasonal mosaic environments — that is, on the savanna.

Now, it's important to know that White played a key role in discovering and describing Ardipithecus. His work has been of great significance to the anthropological community in researching our early origins, and has shifted how most anthropologists describe the savanna's role in our prehistory.

In his Current Anthropology commentary, White offers a wide range of data, including hominin anatomy, paleontology and paleobotany, to support this view that hominin origins occurred outside a savanna context.

This debate is real, and important. As is often the case in paleoanthropology, the relevant data are diverse, inviting divergent interpretation.

But still, why the acidic tone?

One clue exists in White's claim that Dominguez-Rodrigo offers neither original research nor new data. That's a slap from a field worker at a scholar whose conclusions rest on secondary analyses of fossils. In a sense, I'm sympathetic, especially because in this case the analyst, Dominguez-Rodrigo, claims to know fieldwork better than the fieldworker, White. Yet I strongly believe that both approaches are needed for a solid understanding of human-evolution fossils and what they mean for decoding our past.

I asked paleoanthropologist, science writer and Professor Emerita at Penn State University Pat Shipman for her take on the tone of the Dominguez-Rodrigo and White exchange. Once she had read the full back-and-forth, Shipman told me in an email:

"These exchanges smack of personal antipathy, of territorial defense of one's hypothesis, and of a close identification between an interpretation or hypothesis and one's personal honor. Both White and Dominguez-Rodrigo veer rather close to accusing the other of careless scholarship."

Shipman's last sentence is, I think, a polite understatement. But what a good point she makes about honor. Now I can't help but see these two men as engaging in a duel of personal honor, albeit in print.

And that's a problem.

It's sometimes easier said than done, as I know from personal experience, to engage in an attempt to falsify one's own favored, long-labored-over hypothesis — even as we teach our students that doing just that is best practice in science.

Sometimes, of course, the contesting view itself can be falsified. Figuring all this out may be a tangled enterprise, resolvable only with years' more research.

Along the way, scientists can and should debate their views, firmly and with force. Science and passion are not mutually exclusive.

But it's dangerous when a passion for science also becomes a passion for defending one's own honor.

Barbara's most recent book on animals will be released in paperback in April. You can keep up with what she is thinking on Twitter: @bjkingape