关键词: 现代人起源;出自非洲;多地区;中性理论;分子钟

Abstract: In 1983, the first mitochondrial DNA (mtDNA) phylogenetic tree of modern humans suggested that the origin of modern humans might be in Asia. In 1987, a different DNA tree was constructed based on the molecular clock hypothesis that suggested the origin of mtDNA in Africa some 200,000 years ago. Subsequent Y chromosome and autosomal studies also supported the Out-of-Africa model, which became the mainstream theory in molecular evolution. In 2010, the draft sequence of the Neandertal genome suggested that Neandertals might have contributed to the genome of present-day peoples. The Out-of-Africa model (also called recent single origin hypothesis or replacement hypothesis) has been revised as the assimilation model. Many researchers have now openly challenged the molecular clock and the neutral theory as more and more genome sequences have been found to be functional or under natural selection with variations being at the saturation phase, which has made the Out-of-Africa model much less certain than commonly believed. Some researchers have now established a new framework for understanding the saturation and linear phases of genetic diversity puzzle, which should lead to a more complete resolution of the human origins question.

Key words: Modern human origins; Out-of-Africa; Multiregional; Neutral theory; Molecular clock