The Museum of Natural History was always a great pleasure with their mix of artifacts and paintings and archaic curation. I was fascinated by the palaeontology section in general and the hominid section in particular. They had an ancient fossilized tortoise large enough to serve as a camping shelter for me (I was about eight at the time). The magnificent Ichthyosaurus, both the fossilized remains as well as a painting of it in its natural state.
And then the hominids. Staring at the darkened skull cap, jaw bone, tooth or skeletal remains of some ancestral hominid. I was fascinated and tortured by the tongue twisting latin names. Australopithecus robustus, Australopithecus africanus, Australopithecus boisei, Australopithecus afarensis. Homo habilis, Homo sapiens sapiens, Homo erectus, Cro-Magnon, and Neanderthal were easy by comparison. Being a categorizer, I worked hard to try and understand the different lineages and how they all related to one another.
I was, of course, too young to understand that in fact we really didn't understand too much at all. We had remnants and fragments. We were just beginning to put the picture together. As I grew older and read wider, I began to understand the controversy between the out-of-Africa crowd versus the multiregionalist theories of our evolution. Then along came DNA and genetics and ever finer and more sensitive tools to trace lineages and interactions. The discovery that against all the theory I had learned as a child, there was in fact genetic exchange between Neanderthals and early man.
It was quite an education in the tentativeness and fragility of our knowledge. Everything we know is hostage to some new data that either reaffirms or overthrows what we think we know. For practical and short term purposes, we trumpet our knowledge with certainty. Far more certainty than it warrants. But nuances and caveats are steamrollered in the hurly-burly of daily life. There is no room for hesitation or modesty.
All this is brought to mind by Reimagining Humanity by Ian Tattersall.
The haphazard application of species names to every new hominin fossil was a practice that could not continue indefinitely. And in 1950 the ornithologist Ernst Mayr, one of the fathers of the Evolutionary Synthesis, took it upon himself to lecture the paleoanthropologists on the error of their ways. The Synthesis was an elaboration of evolutionary theory that saw most evolutionary change as the gradual accumulation, via natural selection, of small genetic innovations within ancestor-descendant sequences. So Mayr depicted human evolution as the slow modification of a single lineage culminating in Homo sapiens. Among the fifteen hominin genera then described, Mayr said, there was in reality only one: our own genus, Homo. What’s more, the Homo lineage contained only three species: Homo transvaalensis (an early biped) had given rise to Homo erectus, which in turn had evolved into Homo sapiens. Acutely aware that their nomenclatural proliferation lacked any theoretical justification, the paleoanthropologists capitulated. For half a century thereafter, most of them viewed human evolution as a single-minded progression from primitiveness to sapient perfection driven by natural selection: an idea that fit rather well with the undeniable fact that only one hominin exists in the world today.
From the beginning, though, it was obvious that Mayr’s scheme was a huge oversimplification. As fossil discoveries rapidly continued to accumulate, his single lineage began to bulge at the seams. A new image of hominin evolution began to develop.
Extensive additions to the hominin fossil record beginning in the 1960s eventually made it glaringly evident both that many more morphologies are present in that record than could ever be accommodated by Mayr’s minimalist taxonomy, and that the saga of human evolution was immensely more complex than the burnishing of a single lineage.
A hominin family tree that I drew up in 1993 already featured 12 species, spanning the period from 4 million years ago to the present, while one of my recent trees contains twice as many species, scattered over the last 7 million years. Either way, at any one point in the past, several different hominin species typically coexisted, revealing human evolution not as a linear affair but as a process of vigorous and continuing experimentation with the hominin adaptive potential. Homo sapiens is evidently a huge exception in being the sole hominin species on the planet, and its lonely state cannot be taken as a guide to the past. There is something unprecedented about our species that makes it both intolerant of competition and uniquely able to eliminate it.