Saturday, December 10, 2011

Competing Speculative Hypotheses

About a year ago, I wrote a rather lengthy essay (Griswold 2011) inspired by the paleoanthropologist Richard Klein and his ideas regarding the behavioral and cultural changes known as the human great leap forward. Here ( you can watch a recent 45-minute lecture by Dr. Klein on the topic, and although I think his written works (for instance, (Klein 2002) and (Klein 2008)) provide better detail, the video lecture does give a reasonable introduction and overview to Klein's approach and is well worth the short investment of time.

Near the very end of the lecture, after having outlined arguments and evidence for the notion that the human great leap forward was a sudden event—occurring around fifty thousand years ago—Klein states his hypothesis that the sudden event must have been launched by a genetic mutation, one producing significant cognitive effect. Klein then briefly mentions the recent and preliminary work on the mapping of the Neanderthal genome (Green 2010), work that has led to two major (and still preliminary) results: 1. there is now a list (a fairly short list) of modern human/non-Neanderthal gene sequences that would serve as obvious candidates for recent genetic mutation; and 2. nearly all non-African modern humans carry a small influence (estimated in the neighborhood of 2.5%) of Neanderthal-originated genetic material.

As Klein mentions in his lecture, the first result opens the door to a means for testing his genetic mutation hypothesis. The idea would be to obtain a list of modern human genetic sequences that differ significantly from those of ancient humans (including Neanderthals) and see if a subset of these produce the kind of neurological impact consistent with human behavioral and cognitive change. There are of course some technical challenges that stand in the way of this approach: for one, the genome mappings are still in need of greater clarification and accuracy, and furthermore, scientists have not yet been all that successful in connecting genetic material to phenotypic effect, be it cognitive or otherwise. Nonetheless, these are challenges that might be expected to be overcome through technological advances, and so indeed, Klein's hypothesis might one day soon be put to a thorough scientific test.

As I outlined in (Griswold 2011), I'm fairly convinced Klein is going to be disappointed in the results of that test. Although I concur with Klein's assertion that the human great leap forward was a sudden anthropological event, I see an incongruity undermining Klein's explanation for that event. Although most scientists, Klein included, would take for granted that human cognitive advancement must have been driven by a genetic/neurological/evolutionary change, nearly everything scientists can actually demonstrate about genetics, neurology and evolution runs counter to the type of sudden, population-wide, large-scale event Klein is describing. It's as though the animal world had gone sightless for billions of years and then overnight one of the species popped up a pair of excellent eyes and immediately conquered the rest of the planet through this new-found vision. It makes for a dramatic story, but biology doesn't seem to work that way.

Genetically-driven evolutionary change does of course happen, but not on the time or impact scale Klein is proposing (and not even on the time or impact scale that cultural evolutionists would propose). On the one hand, Klein's description of sudden human behavioral and cognitive change looks accurate enough based upon the archaeological evidence, but on the other hand, his explanation for that sudden change looks utterly implausible based upon the logic of biology.

That said, it would still be prudent to wait for the science.

Also in the video lecture, almost as an aside, Klein dismisses the other major finding from Neanderthal genome mapping—the admixture of Neanderthal genetic material into modern humans—suggesting that as details of the respective genomes become more complete and accurate, this finding will prove to be false. Logically speaking, however, Klein doesn't need to make that dismissal: it's perfectly possible that Neanderthal admixture will continue to hold upon further analysis, and yet its impact on human behavioral and cognitive change will prove nonetheless to be benign. I think what's driving Klein's desire to dismiss the admixture finding is that he wants to emphasize how modern Homo sapiens—post genetic mutation—were so cognitively and behaviorally advanced over their Neanderthal contemporaries that all they could do was swamp the Neanderthals into extinction, not interact with or incorporate them. That's a reasonable conclusion to draw given what we already know about European replacement of Neanderthals (evidence for which Klein has intimate working knowledge), but in point of fact there's nothing about the Neanderthal admixture finding that implies it had to be a post out-of-Africa event—the evidence for the timing of that admixture remains inconclusive, and it's quite possible any such admixture could have taken place near the beginning or even prior to the out-of-Africa migration.

Here too, it would be prudent to wait for the science.

My own interest in the Neanderthal admixture finding is that it serves as possible evidence for an alternative explanation to the human great leap forward, an explanation I find logically more plausible—albeit perhaps just as speculative—as Richard Klein's. In (Griswold 2011) I outline how the introduction of autism into the human population—autistic perception in particular—could have served as the catalyst driving human cognitive and behavioral change. I won't repeat the details here, but the concepts at work are a description of autism as a lack of species recognition; autistic perception as a compensatory foregrounding of non-biological pattern, structure, symmetry and form; human cognitive and behavioral advancement as the environmental accumulation of these very same elements of non-biological pattern, structure, symmetry and form; and Neanderthal admixture as the conceivable biological cause for autism-related species dis-recognition. Under my scenario, all these concepts would have come together in a kind of circumstantial stew that began cooking around fifty thousand years ago.

With the ongoing advancements in human genome sequencing, parts of my autism hypothesis might become just as amenable to scientific testing as Klein's genetic mutation hypothesis. The key evidence to look for is whether large or distinctive presences of Neanderthal-derived genetic material within individuals correlates significantly to diagnoses of autism (and perhaps to similar conditions of schizophrenia and bipolar). A high and distinctive correlation would be supportive for describing autism as a condition of species dis-recognition, and thereby indirectly supportive of an autism-related explanation for mankind's great leap forward.

Of course it's also possible that neither speculation—mine nor Richard Klein's—will prove to be helpful, and it will be some other explanation, perhaps one not yet thought of, that manages to untangle the mysteries from fifty thousand years ago. But one thing is for certain: these recent advancements in human genome mapping are opening an intriguing window onto our anthropological past. It's an excellent time to be alive if one is prone to asking such questions as, what caused human beings to become so distinctively human?

(Green 2010): Green, Richard E. and others. 2010. “A Draft Sequence of the Neandertal Genome.” Science 328:710–22

(Griswold 2011): Griswold, Alan. 2011. Autistic Songs. Bloomington, IN: iUniverse.

(Klein 2002): Klein, Richard G. 2002. The Dawn of Human Culture. New York: Wiley.

(Klein 2008): Klein, Richard G. 2008. "Out of Africa and the Evolution of Human Behavior." Evolutionary Anthropology 17:267–81.