Department of Anthropology, University of California, One Shields Avenue, Davis, CA 95616, USA.
J Hum Evol. 2012 Jul;63(1):121-6. doi: 10.1016/j.jhevol.2012.04.003. Epub 2012 Jun 2.
Scenarios for modern human origins are often predicated on the assumption that modern humans arose 200,000-100,000 years ago in Africa. This assumption implies that something 'special' happened at this point in time in Africa, such as the speciation that produced Homo sapiens, a severe bottleneck in human population size, or a combination of the two. The common thread is that after the divergence of the modern human and Neandertal evolutionary lineages ∼400,000 years ago, there was another discrete event near in time to the Middle-Late Pleistocene boundary that produced modern humans. Alternatively, modern human origins could have been a lengthy process that lasted from the divergence of the modern human and Neandertal evolutionary lineages to the expansion of modern humans out of Africa, and nothing out of the ordinary happened 200,000-100,000 years ago in Africa. Three pieces of biological (fossil morphology and DNA sequences) evidence are typically cited in support of discrete event models. First, living human mitochondrial DNA haplotypes coalesce ∼200,000 years ago. Second, fossil specimens that are usually classified as 'anatomically modern' seem to appear shortly afterward in the African fossil record. Third, it is argued that these anatomically modern fossils are morphologically quite different from the fossils that preceded them. Here I use theory from population and quantitative genetics to show that lengthy process models are also consistent with current biological evidence. That this class of models is a viable option has implications for how modern human origins is conceptualized.
现代人种起源的情景通常基于这样一种假设,即现代人种起源于 20 万至 10 万年前的非洲。这种假设意味着在非洲的这个时间点上发生了一些“特殊”的事情,例如产生智人的物种形成、人类种群规模的严重瓶颈,或者两者的结合。共同的线索是,在现代人类和尼安德特人进化谱系大约 40 万年前分化之后,在中更新世晚期边界附近又发生了另一个离散事件,产生了现代人类。或者,现代人种起源可能是一个漫长的过程,从现代人类和尼安德特人进化谱系的分化一直持续到现代人类从非洲扩张,而在 20 万至 10 万年前的非洲没有发生任何不寻常的事情。通常有三个生物学证据(化石形态和 DNA 序列)支持离散事件模型。首先,现代人类线粒体 DNA 单倍型在大约 20 万年前汇聚。其次,通常被归类为“解剖学上现代”的化石标本似乎在之后不久就出现在非洲化石记录中。第三,有人认为这些解剖学上的现代化石在形态上与它们之前的化石有很大的不同。在这里,我使用种群和数量遗传学的理论来表明,漫长的过程模型也与当前的生物学证据一致。这类模型是一个可行的选择,这对如何理解现代人种起源具有影响。