Thanks to Ed Yong several people on twitter have encountered my post, The point mutation which made humanity. My broader concern which I was attempting to highlight is that too often when we attempt to ascertain the origins of modern human success in relation to our archaic cousins/ancestors we presume that there must be a qualitative species-wide difference. So, for example, it used to be bandied about that a large effect mutation conferred upon the ancestors of modern humans the ability to speak with the fluency which we take for granted. For various reasons that seems less and less plausible.
But even my thin knowledge of archaeology does indicate that what remains plausible is that modern humans exhibited a level of scale in their group-size, as well as extended force projection, and the ability to rapidly traverse difficult territory. It was modern humans who pushed the frontier to Australia and the New World, even if some archaic lineages did brush up against the margins (e.g., Flores). This sort of concerted and somewhat crazy outward projection of numbers probably required greater specialization and integration of the various groups which would have to operate as a unit as they pushed the frontier outward. One way you can increase the flexibility of a group is by increasing the competencies of individual members of the group. So a large subspecies level difference between modern humans and Neandertals might explain why the former could scale up into larger and more effective groups. But another possibility is that a minority phenotype emerged among modern humans, and this phenotype was correlated with a set of strategies and personalities which allowed for improved coordination amongst who lacked the phenotype. A powerful leader with organizational drive. So, for example, the well fed Gauls that confronted Caesar’s legions may well have been more robust on a per person basis than the Romans, thanks to their protein rich diet. But the coordination of the legions, and the discipline of the troops, allowed them to grind away at their until they were crushed. That Republican Roman discipline did not exist in a cultural vacuum. For the clans of Latium to transform themselves into the mega-city of the ancient world there had to be a series of competent leaders such as Scipio Africanus to drive the process forward.
Plots like the one to the left (credit: Luke Jostins) illustrate that there were broad concurrent trends across the human lineage. More recently there have been parallel events such as the emergence of agriculture in distinct hearths after the Ice Age. Perhaps modern human civilization as we understand isn’t such a contingent miracle, and the process was already made nearly inevitable ~5 million years ago as the hominins began to hurtle toward some terminus, yet to be determined? If so, the “human journey” may not exhibit so many biological breaks which can be easily discerned from examining the physique or genomes of modern humans and our archaic relatives. Rather, the great cultural breaks which we can perceive in the physical record may simply reflect rapid shifts driven by a few, and catalyzed by the collective coordination of groups which were turned into the extension of the vision of charismatic leaders.
I don’t really believe the story above. But I do believe it more at this point than the possibility that we can find the gene which is responsible for making us human. And I’m someone who is quite willing to find genes responsible for great things….