Li W H, Tanimura M, Sharp P M
Center for Demographic and Population Genetics, University of Texas, Houston 77225.
J Mol Evol. 1987;25(4):330-42. doi: 10.1007/BF02603118.
A statistical analysis of extensive DNA sequence data from primates, rodents, and artiodactyls clearly indicates that no global molecular clock exists in mammals. Rates of nucleotide substitution in rodents are estimated to be four to eight times higher than those in higher primates and two to four times higher than those in artiodactyls. There is strong evidence for lower substitution rates in apes and humans than in monkeys, supporting the hominoid slowdown hypothesis. There is also evidence for lower rates in humans than in apes, suggesting a further rate slowdown in the human lineage after the separation of humans from apes. By contrast, substitution rates are nearly equal in mouse and rat. These results suggest that differences in generation time or, more precisely, in the number of germline DNA replications per year are the primary cause of rate differences in mammals. Further, these differences are more in line with the neutral mutation hypothesis than if the rates are the same for short- and long-living mammals.
对来自灵长类动物、啮齿动物和偶蹄目动物的大量DNA序列数据进行的统计分析清楚地表明，哺乳动物中不存在全球分子钟。据估计，啮齿动物的核苷酸替换率比高等灵长类动物高4至8倍，比偶蹄目动物高2至4倍。有强有力的证据表明，猿类和人类的替换率低于猴子，这支持了类人猿减速假说。也有证据表明人类的替换率低于猿类，这表明人类与猿类分离后，人类谱系中的替换率进一步放缓。相比之下，小鼠和大鼠的替换率几乎相等。这些结果表明，世代时间的差异，或者更准确地说，每年生殖系DNA复制的次数差异，是哺乳动物速率差异的主要原因。此外，这些差异更符合中性突变假说，而不是短寿命和长寿命哺乳动物的速率相同的情况。
