Anyone who has studied the concept of Natural Selection knows that one of the requirements is a variable population. Adaptation to a changing environment cannot occur if every individual in the population is very similar. So, variability is a given. However, when scientists look at fossil material, many of them seem to forget this important tenet. Any differences they find in fossil material are given, minimally, a new species name, and frequently, a new genus name. That fossil then becomes the type specimen of a new species, and any other material found in that region that looks different will be given yet another new species name instead of considering whether, in fact, it is just a new individual in a variable population.
Or, in the case of dinosaurs, a juvenile rather than a small adult of a different species. Jack Horner’s TED talk on this topic is both amusing and enlightening. Paleontologists who focused on differences created many dinosaur species which had no juvenile forms. Horner felt that this was not only odd, but clearly impossible. By carefully analyzing the skeletons, he discovered that many species of dinosaurs were just the juvenile forms of other species. The focus on differences was a mistake.
Focusing on differences and assigning new species names to every new find is also common among many paleoanthropologists who study primate/human origins. Natural selection and population variability are thrown out the door. If we treated present human diversity the way we treat past diversity, every different population of humans would be a different species. We know this is not the case since all humans can potentially mate with each other.
There are two major groups of paleoanthropologists: those who operate from a population viewpoint and those who operate from an essentialist viewpoint. For instance, populationists view Neanderthals as a population of modern humans, while essentialists view Neanderthals as a different species. Why does this matter to the average person? It matters because the underlying viewpoints affect how we view each other. Essentialists view anyone who differs from their idea of the ‘norm’ (generally someone like themselves, i.e. of European ancestry) as deeply biologically distinct from themselves. In effect, that there are distinct races of humans that are somehow quite different from each other. Populationists, on the other hand, expect there to be many people who differ from themselves because that is what a successful, adaptable population requires. They do not view these differences as creating deep distinctions. That is, they do not view humans as being divided into distinct racial groups. Rather, humans form varying, over-lapping, constantly mixing populations. They also hold that this has been true since the beginning of the Homo genus.
Genes flow, drift, mutate, select, and adapt as the individuals carrying those genes meet, mate, and adapt. For the past two million years our ancestors have been meeting,mating, mixing, and adapting to differing environments as one unified, but variable species. Just as the lack of juvenile dinosaurs was an artifact of paleontologists who operated from an essentialist mindset, the many “species” of human ancestors are an artifact of paleoanthropologists who operate from an essentialist mindset. The juvenile dinos were there all along. The necessary variability of the human population that allows it to adapt to the vast array of environments on our planet has been there all along, too. The essentialist’s mistake has been to divide that variability into different species or races.
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