Center for Study of Human Origins, Department of Anthropology, New York University, New York, NY 10003, USA.
Am J Phys Anthropol. 2012;149 Suppl 55:24-39. doi: 10.1002/ajpa.22159. Epub 2012 Nov 2.
For much of the 20th century, the predominant view of human evolutionary history was derived from the fossil record. Homo erectus was seen arising in Africa from an earlier member of the genus and then spreading throughout the Old World and into the Oceania. A regional continuity model of anagenetic change from H. erectus via various intermediate archaic species into the modern humans in each of the regions inhabited by H. erectus was labeled the multiregional model of human evolution (MRE). A contrasting model positing a single origin, in Africa, of anatomically modern H. sapiens with some populations later migrating out of Africa and replacing the local archaic populations throughout the world with complete replacement became known as the recent African origin (RAO) model. Proponents of both models used different interpretations of the fossil record to bolster their views for decades. In the 1980s, molecular genetic techniques began providing evidence from modern human variation that allowed not only the different models of modern human origins to be tested but also the exploration demographic history and the types of selection that different regions of the genome and even specific traits had undergone. The majority of researchers interpreted these data as strongly supporting the RAO model, especially analyses of mitochondrial DNA (mtDNA). Extrapolating backward from modern patterns of variation and using various calibration points and substitution rates, a consensus arose that saw modern humans evolving from an African population around 200,000 years ago. Much later, around 50,000 years ago, a subset of this population migrated out of Africa replacing Neanderthals in Europe and western Asia as well as archaics in eastern Asia and Oceania. mtDNA sequences from more than two-dozen Neanderthals and early modern humans re-enforced this consensus. In 2010, however, the complete draft genomes of Neanderthals and of heretofore unknown hominins from Siberia, called Denisovans, demonstrated gene flow between these archaic human species and modern Eurasians but not sub-Saharan Africans. Although the levels of gene flow may be very limited, this unexpected finding does not fit well with either the RAO model or MRE model. More thorough sampling of modern human diversity, additional fossil discoveries, and the sequencing of additional hominin fossils are necessary to throw light onto our origins and our history.
在 20 世纪的大部分时间里，人类进化史的主要观点源自化石记录。直立人被认为起源于非洲，是更早的人类属种的后裔，然后扩散到旧大陆，并进入大洋洲。一种区域连续的进化模式认为，从直立人通过各种古老的中间物种逐渐演变成每个直立人居住地区的现代人类，这种模式被称为人类进化的多区域模型（MRE）。另一种相反的模式则假设，解剖学上的现代智人起源于非洲，一些人口后来从非洲迁徙出去，并在全球范围内取代了当地的古老人口，这种模式被称为近期非洲起源（RAO）模型。这两种模式的支持者几十年来都一直使用对化石记录的不同解释来支持自己的观点。20 世纪 80 年代，分子遗传学技术开始从现代人类的变异中提供证据，不仅允许对现代人类起源的不同模型进行测试，还允许探索人口历史以及基因组不同区域甚至特定特征所经历的选择类型。大多数研究人员将这些数据解释为强烈支持 RAO 模型，尤其是对线粒体 DNA（mtDNA）的分析。从现代变异模式推断，使用各种校准点和替代率，人们达成了一个共识，即现代人类大约在 20 万年前从非洲人口中进化而来。在此之后很久，大约在 5 万年前，这部分人口从非洲迁徙出去，取代了欧洲和西亚的尼安德特人以及东亚和大洋洲的古老人类。来自 20 多个尼安德特人和早期现代人类的 mtDNA 序列进一步证实了这一共识。然而，2010 年，尼安德特人和西伯利亚未知原始人类（称为丹尼索瓦人）的完整基因组草图表明，这些古老人类物种与现代欧亚人之间存在基因流动，但与撒哈拉以南非洲人没有基因流动。尽管基因流动的水平可能非常有限，但这一意外发现与 RAO 模型或 MRE 模型都不太相符。需要更全面地采样现代人类的多样性，发现更多的化石，并对更多的原始人类化石进行测序，以便揭示我们的起源和历史。
