Molecular Approach to the Phylogeny of Primates and Other Placental Mammals

虽然胎盘哺乳动物的系统发育和系统分类学研究取得了很大进展，但仍存在许多难题。这些问题不仅涉及以人类为成员的灵长类目，还涉及其他17目胎盘哺乳动物。例如，最重要的灵长类动物群体之一是由新世界猴和狨猴组成的超级科，但在过去的2500万年里，从一个共同的祖先进化到这些新热带灵长类动物的16个属的进化模式却鲜为人知。同样，发生在9000万至6500万年前的一系列系统发育分支事件将现存的18目胎盘哺乳动物彼此分开，但分支的确切过程，即这些主要胎盘哺乳动物群体之间的进化关系，尚未明确确定。近年来分子生物学的技术进步使得从大量物种的相应基因中获得大量的DNA核苷酸序列数据成为可能。由于DNA中的核苷酸序列是遗传或可遗传的物质，这些信息提供了比较物种进化关系的非常精确的记录。通过利用新的分子方法生成比较核苷酸序列数据，将从上述哺乳动物群体中获得几个不同基因的DNA信息。这些数据将受到严格的系统发育分析，使用基于理论模型的计算机程序，最好地描述基因随时间变化的过程。这种系统发育分析，当应用于基因中更快速进化部分的DNA序列数据时，有望为16属新热带灵长类动物之间存在的进化关系提供高度清晰的图像。同样地，这种分析应用于较慢旋转的基因部分，应该可以很好地解决胎盘哺乳动物18目之间存在的进化关系。除了重建系统发育分支的模式外，还将确定沿分支的DNA变化率。当与研究中动物的生活史策略相关时，这些关于比率的信息将验证这样一个假设，即生活史向更长的世代变化和寿命导致DNA突变率下降，而生活史向更短的世代变化和寿命导致DNA突变率增加。

Although much progress has been made in elucidating the phylogeny and systematics of placental mammals, many difficult problems still remain. These problems involve not only the order Primates, which has humans among its members, but also the 17 other orders of placental mammals. For example, one of the most important primate groups is the superfamily Ceboidea comprised of New World monkeys and marmosets, but the pattern of evolution over the last 25 million years that led from a common ancestor to the 16 surviving genera of these neotropical primates is poorly understood. Similarly, a series of phylogenetic branching events that occurred between 90 and 65 million years ago separated the 18 surviving orders of placental mammals from one another, but the exact course of branching, i.e. the evolutionary relationships among these major groups of placental mammals, has yet to be definitively established. Recent technical advances in molecular biology have made it possible to obtain large amounts of DNA nucleotide sequence data from corresponding genes in a wide range of species. Since the sequence of nucleotide in DNA is the genetic or heritable material, such information provides a very precise record of the evolutionary relationships of the species compared. Through utilizing the new molecular methods for generating comparative nucleotide sequence data, DNA information from several different genes will be obtained from the above mentioned mammalian groups. These data will be subjected to rigorous phylogenetic analysis, using computer programs based on theoretical models that best describe the course of genetic change over time. This phylogenetic analysis, when applied to the DNA sequence data from the more rapidly evolving portions of the genes, is expected to provide a highly resolved picture of the evolutionary relationships that exist among the 16 genera of neotropical primates. Similarly, this analysis applied to the slower revolving genic portions should provide a well resolved picture of the evolutionary relationships that exist among the 18 orders of placental mammals. In addition to reconstructing the pattern of phylogenetic branching, rates of DNA change along the branches will be determined. This information on rates, when related to knowledge on the life history strategies of the animals included in the study, will test the hypothesis that life history changes towards longer generation times and life spans cause decreases in DNA mutation rates, whereas life history changes towards shorter generation times and life spans cause increases in DNA mutation rates.