新证据下的现代人起源模型

Modeling the origin of modern humans in light of new evidence

解剖结构上的现代人是指具有近圆球形头骨、短而平的面颅、纤细的骨骼等特征的区别于其他古老人类的化石和现今的人群。支持多地区演化模型和支持近期非洲起源模型的学者,在“解剖结构上的现代人”的应用范围方面是不同的,前者以连续演化为基本思想,认为这一名词只包括智人中较进步的类群;而后者以分支系统学思想为基础,认为包括所有智人。分子古生物学研究显示,尼人、丹人和智人在遗传学水平上属于不同的人种。新近的以标本-种群为单元的系统分析,因为不是以属、种等分类学阶元进行的,因此与分类学的阶元划分无关。该系统分析的结果显示智人属于单系类群,哈尔滨人、大荔人等组成其姊妹群。尼人与智人的分异早于1百万年,与基因组水平的谱系分析相符合。多次多向的穿梭扩散是统计学上符合系统关系的模型。

Anatomically modern human(AMH)is a term used for living and fossil humans that have globular skull,short and flat face,gracile skeleton,and a set of other osteological distinctive features different from most of the archaic humans.Researchers,who take Multiregional Evolution model(MEM)as their paradigm,use AMH as a counter part of archaic Homo sapiens,while Recent African Origin(RAO)supporters use the term for all H.sapiens.MEM was derived from continuous evolution ideology.Branching evolution was believed to be negligible during the rise of modern populations.The similarities between different local populations were regarded as the results of convergent evolution.RAO on the other hand suggests that human evolution follows the cladistic form as in the other creatures.AMHs belong to a monophyletic group and have a single origin in Africa.Non-African human populations dispersed out of Africa.Archaic human populations in Europe and Asia were replaced by the anatomically modern human during the dispersal of the latter,and there were very limited genetic exchanges between modern and archaic human populations.Recent advances in ancient DNA and proteomic researches revealed that inter-specific interbreeding did occur among H.sapiens,H.neanderthalensis and the unnamed Denisovan populations.Genomic analyses,however,indicate that regions with a high frequency of Neanderthal derived alleles in modern human genomes are mostly related to deleterious genes.Strong reproductive isolation between modern humans and Neanderthals was also detected.Instead of supporting the multiregional model,the molecular data actually reveals that modern humans,Neanderthals and Denisovans are all belong to their own species at genetic level.Debates over taxonomic assignments of some specific fossils may not be helpful for detecting the evolutionary pattern of Homo in general and the origin of H.sapiens in particular,because most of recent comparisons and analyses are at specimen or population levels,not at species level.Our recent parsimony analyses and Bayesian inferring based on large data matrix revealed that the AMHs formed a monophyletic group.Another monophyletic clade represented by Dali and Harbin skulls is the sister of this group.The divergent time between Neanderthals and AMHs is over 1 million years.This estimation is much older than previous aDNA inferring,but is consistent with the recent results based on genome-wide genealogical analyses.Biogeographic model tests also reveal that a model including multiple multi-directional dispersals among Asia,Europe and Asia statistically fits the phylogenetic tree better than the MEM and RAO.