The rate of human morphological microevolution and taxonomic diversity of hominids

Hominid evolution can be interpreted either as a series of speciation events producing new morphological patterns or as an anagenetic process in a single-taxon lineage resulting in gradual changes of morphological characters. Studies of changes of metric characteristics of humans during the Holocene indicate that a substantial change in morphology can occur within a few thousand years. Reduction in cranial capacity by 100–150 millilitres (approximately one standard deviation) is a prominent example. The general decrease in the size of the human body occurred from the Upper Pleistocene to the Middle Ages. It was only partially reversed in the last 100 years by secular trends. Substantial reduction in the size of human dentition occurred during the Holocene. All these changes occurred during time periods that are comparable with the ranges of uncertainties of geological and radiometric dating methods that are applied to a period before the last 25 Ka. Thus, to a student of palaeoanthropology transitions observable in the fossil record may appear to be instantaneous as if they were a result of the replacement of one taxon by the other even if they were results of gradual, but rapid microevolutionary changes. Thus a scenario of interbreeding human populations evolving towards so-called ‘modern human anatomy’ is possible. This scenario is more likely in terms of the population genetics evolutionary mechanisms than a sudden emergence of stable morphologies of many species and their abrupt extinctions.