UPDATED 11/24/13 AND 02/11/14
Have you read about Skull 5, a 1.8-million-year-old fossil? Well, it has been in the news lately. Here’s some of the coverage:
Scientists trying to unravel the origins of humanity mostly study scraps — some ancient teeth here, a damaged bone there. But now a lucky research team has uncovered a fossil superstar: the first complete skull of an early human adult from the distant past.
The 1.8-million-year-old fossil, known as Skull 5, is like nothing seen before. It has a small brain case and a heavy, jutting jaw, as did some of humanity’s older, more apelike ancestors. But other bones linked to Skull 5 show its owner had relatively short arms and long legs, as does our own species, Homo sapiens. Those who’ve studied Skull 5 say it also provides support for the provocative idea that, 1.8 million years ago, only one kind of early human held sway, rather than the throng of different species listed in today’s textbooks….
Paleoanthropologist Susan Antón of New York University, while praising the new analysis, says the Dmanisi team didn’t compare fossil features, such as the anatomy around the front teeth, that differ most starkly between two different species of early humans. So the Dmanisi team’s hypothesis that there was only one lineage is not totally convincing, she says… (Traci Watson, “Skull Discovery Sheds Light on Human Species,” USA Today, October 17, 2013)
In the eastern European nation of Georgia, a group of researchers has excavated a 1.8 million-year-old skull of an ancient human relative, whose only name right now is Skull 5. They report their findings in the journal Science, and say it belongs to our genus, called Homo.
“This is most complete early Homo skull ever found in the world,” said lead study author David Lordkipanidze, researcher at the Georgian National Museum in Tbilisi….
The variation in physical features among the Dmanisi hominid specimens is comparable to the degree of diversity found in humans today, suggesting that they all belong to one species, Lordkipanidze said….
Now it gets more controversial: Lordkipanidze and colleagues also propose that these individuals are members of a single evolving Homo erectus species, examples of which have been found in Africa and Asia. The similarities between the new skull from Georgia and Homo erectus remains from Java, Indonesia, for example, may mean there was genetic “continuity across large geographic distances,” the study said.
What’s more, the researchers suggest that the fossil record of what have been considered different Homo species from this time period — such as Homo ergaster, Homo rudolfensis and Homo habilis — could actually be variations on a single species, Homo erectus. That defies the current understanding of how early human relatives should be classified….
The Dmanisi fossils are a great find, say anthropology researchers not involved with the excavation. But they’re not sold on the idea that this is the same Homo erectus from both Africa and Asia — or that individual Homo species from this time period are really all one species.
“The specimen is wonderful and an important contribution to the hominin record in a temporal period where there are woefully too few fossils,” said Lee Berger, paleoanthropologist at the University of the Witwatersrand in Johannesburg, in an e-mail.
But the suggestion that these fossils prove an evolving lineage of Homo erectus in Asia and Africa, Berger said, is “taking the available evidence too far.”
…He criticized the authors of the new study for not comparing the fossils at Dmanisi to A. sediba or to more recent fossils found in East Africa…. (Elizabeth Landau, “Skull Sparks Human Evolution Controversy,” CNN, October 19, 2013)
I will go further and say this: Even if 1.8 million years ago there was a single species from which today’s human beings are descended, today’s human beings don’t necessarily belong to a single species or sub-species.
In fact, some reputable scientists have advanced a theory that is consistent with racial divergence:
Gregory Cochran and Henry Harpending begin The 10,000 Year Explosion [link added] with a remark from the paleontologist Stephen J. Gould, who said that “there’s been no biological change in humans for 40,000 or 50,000 years.” They also cite the evolutionist Ernst Mayr, who agrees that “man’s evolution towards manness suddenly came to a halt” in the same epoch. Such claims capture the consensus in anthropology, too, which dates the emergence of “behaviorally modern humans” — beings who acted much more like us than like their predecessors — to about 45,000 years ago.
But is the timeline right? Did human evolution really stop? If not, our sense of who we are — and how we got this way — may be radically altered. Messrs. Cochran and Harpending, both scientists themselves, dismiss the standard view. Far from ending, they say, evolution has accelerated since humans left Africa 40,000 years ago and headed for Europe and Asia.
Evolution proceeds by changing the frequency of genetic variants, known as “alleles.” In the case of natural selection, alleles that enable their bearers to leave behind more offspring will become more common in the next generation. Messrs. Cochran and Harpending claim that the rate of change in the human genome has been increasing in recent millennia, to the point of turmoil. Literally hundreds or thousands of alleles, they say, are under selection, meaning that our social and physical environments are favoring them over other — usually older — alleles. These “new” variants are sweeping the globe and becoming more common.
But genomes don’t just speed up their evolution willy-nilly. So what happened, the authors ask, to keep human evolution going in the “recent” past? Two crucial events, they contend, had to do with food production. As humans learned the techniques of agriculture, they abandoned their diffuse hunter-gatherer ways and established cities and governments. The resulting population density made humans ripe for infectious diseases like smallpox and malaria. Alleles that helped protect against disease proved useful and won out.
The domestication of cattle for milk production also led to genetic change. Among people of northern European descent, lactose intolerance — the inability to digest milk in adulthood — is unusual today. But it was universal before a genetic mutation arose about 8,000 years ago that made lactose tolerance continue beyond childhood. Since you can get milk over and over from a cow, but can get meat from it only once, you can harvest a lot more calories over time for the same effort if you are lactose tolerant. Humans who had this attribute would have displaced those who didn’t, all else being equal. (If your opponent has guns and you don’t, drinking milk won’t save you.)
To make their case for evolution having continued longer than is usually claimed, Messrs. Cochran and Harpending remind us that dramatic changes in human culture appeared about 40,000 years ago, resulting in painting, sculpture, and better tools and weapons. A sudden change in the human genome, they suggest, made for more creative, inventive brains. But how could such a change come about? The authors propose that the humans of 40,000 years ago occasionally mated with Neanderthals living in Europe, before the Neanderthals became extinct. The result was an “introgression” of Neanderthal alleles into the human lineage. Some of those alleles may have improved brain function enough to give their bearers an advantage in the struggle for survival, thus becoming common.
In their final chapter, Messrs. Cochran and Harpending venture into recorded history by observing two interesting facts about Ashkenazi Jews (those who lived in Europe after leaving the Middle East): They are disproportionately found among intellectual high-achievers — Nobel Prize winners, world chess champions, people who score well on IQ tests — and they are victims of rare genetic diseases, like Gaucher’s and Tay-Sachs. The authors hypothesize that these two facts are connected by natural selection.
Just as sickle-cell anemia results from having two copies of an allele that protects you against malaria if you have just one, perhaps each Ashkenazi disease occurs when you have two copies of an allele that brings about something useful when you have just one. That useful thing, according to Messrs. Cochran and Harpending, is higher cognitive ability. They argue that the rare diseases are unfortunate side-effects of natural selection for intelligence, which Messrs. Cochran and Harpending think happened during the Middle Ages in Europe, when Jews rarely intermarried with other Europeans. (Christopher F. Chabris, “Last-Minute Changes,” The Wall Street Journal, February 12, 2009)
It is said that, despite the differences across races, all humans beings have in common 96 percent of their genes. Well, if I told you that humans and chimpanzees have about the same percentage of their genes in common, would you consider chimpanzees to be nothing more than superficially different human beings who belong to the same sub-species? Just remember this: The “species problem” remains unsolved.
So what if human beings belong to a variety of different sub-species? A candid scientific admission of that fact would put an end to the nonsense the “we’re all the same under the skin.” We”re not, and it’s long past time to own up to it, and to quit using the power of the state to strive for a kind of equality that is unattainable.
Although there are out-and-out disbelievers and cautious skeptics, some recent research in a field known as epigenetics suggests that behavioral conditioning can yield heritable traits. If true, it means that evolution is shaped by cultural influences, thus reinforcing positive traits (e.g., hard work and law-abidingness) among those people who possess and inculcate such traits, while also reinforcing negative traits (e.g., violence, shiftlessness) among those people who possess inculcate such traits.
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Gregory Gorelik and Todd D. Shackleford, “A Review of Gregory Cochran and Henry Harpending, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution,” Evolutionary Psychology, 2010. 8(1): 113-118
Carl Zimmer, “Christening the Earliest Members of Our Genus,” The New York Times, October 24, 2013