The molecular models of modern human origins

<p indent="0mm">In the early 1960s, researchers started the field of molecular evolution based on the genetic distance phenomenon of protein sequences among species, and proposed a molecular evolutionary theory different from the natural selection theory, the molecular clock hypothesis and the neutral theory. This theory holds that the genetic distance of gene sequences can be used to infer the phylogenetic relationship between different species. The greater the genetic distance, the farther the phylogenetic relationship and the longer the evolutionary time. Researchers then deduced a molecular model of the origin of modern humans based on this theory, the recent out of Africa hypothesis. African populations have the highest genetic diversity among all racial groups, which was interpretated to mean that Africans have a more ancient most recent common ancestor than other populations. Modern humans are considered to have first appeared in Africa who then migrated to Eurasia and largely replaced the indigenous populations. Although the neutral theory is a very valuable null hypothesis, it cannot fully explain the phenomenon of genetic diversity, which therefore deems the out-of-Africa model, at best, uncertain. In 2008, a new theory of molecular evolution, known as the maximum genetic diversity theory, was published, offering a reinterpretation of the phenomenon of genetic distances. A large genetic distance does not necessarily mean a long evolutionary time, but can also reflect a large phenotypic difference. The increase in genetic distance over time is not infinite, as implied by the neutral theory, but has an upper limit, which is mainly determined by the phenotypic complexity of the species. Several lines of tests show that the genetic distances or genetic diversities are largely at the upper limit levels. Based on the maximum genetic diversity theory, new research has independently re-discovered the out of East Asia model of modern humans that was first proposed in 1983. It also provides autosomal DNA support for the multiregional hypothesis. Multiple lines of tests, including ancient DNA analyses, lend robust support to the out of East Asia model as the more accurate representation of modern human origins. As exploration of the fundamental theories of evolution deepens, humanity′s understanding of its own origins is destined to become clearer and more refined.