by Doctor Science
Carl Zimmer is a great science writer I've been following for years. It's not really his fault that his latest NY Times article on human evolution was the last straw for me, finally breaking my ability to quietly tolerate a particular turn of phrase.
The headline for Zimmer's article is: "A Single Migration From Africa Populated the World, Studies Find".
No. Homo sapiens never "migrated" out of Africa. We did not "trek", "emerge", "exodus", or "journey", either. All such travel-based metaphors misrepresent human evolution, and get both the general public and paleoanthropologists themselves into bad mental habits. These metaphors are also (I believe) racist, which is an even worse mental habit.
What Zimmer and the scientists he profiles are calling "migration" is really range expansion. Other animals (and plants) do this all the time, it's not anything unique to humans.
For instance, the Coyote used to be found only on the Great Plains, but since the end of the 19th century its range has expanded to cover most of North America:
Another example is the Cattle Egret. Native to Africa and the Mediterranean, birds that landed in South America accidentally established a population in the early 20th century, and have expanded to all cattle-ranching areas of the Western Hemisphere today:
Range expansion is an important area of ecology and evolutionary studies, the topic of a great deal of past and ongoing research. So why don't we use those words when we're talking about humans? Why don't even scientists do so?
One reason, I think, is romantic reification. There's a very long-standing custom of talking about human evolution and history as though it's about a single figure or character, Man. The Ascent of Man, Man Discovers Fire, Evolution of Man, etc. Man is a very active and even heroic character, he Does Things. "Range expansion" sounds dull and even passive; Man is special: he conquers, colonizes, treks. Man also has feelings and goals not shared by mere coyotes or herons, so you get article titles like Population genetics: A map of human wanderlust -- as though human range expansion is driven by emotions, unlike that of mere animals.
But romanticism is only part of it. I think another driver of these sloppy metaphors is racism: specifically, a deep reluctance to accept that humans are all fundamentally African, that our species is native to Africa and *only* Africa.
I'm not saying that Zimmer, for example, is consciously motivated by racism. But there's a racist framework in the field of human evolution, and it keeps people in the habit of writing (and thinking) in racist ways.
Humans never left Africa, any more than Cattle Egrets did. The ranges of the Cattle Egret and Homo sapiens have expanded to cover very large areas outside of Africa, but their African populations are still there.
When Zimmer writes:
People everywhere descend from a single migration of early humans from Africa ... Why leave Africa at all? Scientists have found some clues to that mystery, too.-- the picture he evokes implies that humans, real people, are not found in Africa today, they "left" or "migrated" away.
Zimmer is just following the conventions of the field. For instance, among the associated papers at Nature that he reports on, one talks about
the exodus of Homo sapiens out of Africa and into EurasiaAn "exodus" is a departure: this phrase is literally saying that (real) humans were no longer found in Africa, they had moved to Eurasia. It's only from context that we know that's not what the authors "really mean" -- but it's bad writing, bad science, and a really bad mental habit.
And then, on the sidebar of the Nature article, there's an audio file in which
Adam Levy investigates how new pieces of the puzzle are revealing our ancestors' journey out of Africa-- as though "our" ancestors are all from non-African populations.
It's possible there's another element besides romanticism and racism: a clash of scientific dialects. My training is in evolutionary biology & ecology, where "migration" means regular, there-and-back-again travels. Creatures appearing in new places is a completely different phenomenon: "dispersal", "range expansion" or "invasion".
It seems that in archaeology & anthropology "migration" covers almost any movement of peoples -- like an archaeology course on Great Migrations, which covers
the Phoenician diaspora, Greek colonization, Roman veteran settlement, the ‘Sea Peoples' and Visigoth invasions ... labor and pastoral mobility, the Assyrian trade diaspora and the ‘port Jews'.When such social scientists talk about "migration", they often seem to mean events like the Exodus of the Hebrew Bible, where most or all of a community moves from point A to point B in a single generation. Biologists would call this kind of movement a "shift", not a migration, and would expect it to take many generations.
Some scientists are definitely aware how problematic "migration" and other travel-based metaphors are when talking about human evolution. Here's a good example: The great human expansion, by Stanford's Brenna Henn (now at SUNY Stony Brook), Luigi Luca Cavalli-Sforza, and Marcus Feldman. Henn et al. are careful to call the phenomenon they're studying (range) "expansion", and using "migration" only sparingly:
Scientists and (even more important) science writers really need to stop using romantic and racist travel metaphors when talking about human evolution. It's not all that difficult, really: look at your work and ask, "does it sound like I'm saying that African humans aren't as human as people outside of Africa?" If you are, then you'd better change that sentence.