Geographic Variation in Primates A Review with Implications for Interpreting Fossils (original) (raw)

oretical when macaques, closely related or not, are disjunct (allopatric) in their geographic distributions (e.g., the many insular forms of M. fascicularis found throughout Southeast Asia are all reproductively isolated from one another, as is M . sylvanus from North Africa from all the Asian macaques). The endemic radiation of macaques on Sulawesi, as outlined in a later discussion of the group, provide further testimony about the range of interbreeding typically found among evolving primates. Godfrey and Marks' (1991) review, Groves' (this volume) report on gibbons, andJolly's (this volume) account of baboons confirm the commonplace nature of intermediate levels of reproductive isolation in taxonomically distinct primates. As macaques, baboons, and gibbons illustrate, there can be a diversity of relationships among primates living at any one time, either present or past. Our listing of various states of reproductive isolation in macaques is not meant to imply anything about degrees, stages, or sequences in the process of genetic divergence during speciation. Our point is simply that relationships among primates are complex, and this presents problems for primate taxonomists who are trying to determine whether the animals they study are species or not. This point is applicable no matter what species concepts are invoked and no matter what modes of speciation are thought to be active. Given unlimited scientific resources, researchers would be addressing questions about speciation in the field by investigating the details of interactions among local populations. Questions of interest would relate to interbreeding, gene exchange, selection, and fine-grained analyses of behavioral and morphological adaptations. Practicality, of course, imposes a different reality with respect to species determinations, that is, taxonomic studies usually rely on assessments of morphological variation in specimens collected from the wild and preserved in museum collections (i.e., the "phenodata" of Jolly, this volume). Morphological variation is then used to make statements about genetic divergence, reproductive isolation, or other issues of interest. However, as also emphasized by Shea et al. (this volume), these statements are only inferences, since museum studies, based as they are on static samples drawn from a changing world, can provide only indirect evidence about the dynamic evolutionary processes of speciation. Actual genetic data and field observations on wild populations are welcome supplements, but such information is available only in a minority of cases and, even then, often is limited in scope to a few localities. Moreover, such information is often as problematic as inferences drawn from the morphological analysis of museum specimens. Geographic variation is common in primates. Our modern classification of primates would not exist without the cumulative effect of hundreds of studies documenting geographic variation. Primate taxonomists rely on identifying and then assessing the significance of geographic differences in external morphology, especially color and pattern of the pelage. The overwhelming importance of external appearance has been emphasized historically (e.g., Pocock, l 925a,b) and is equally evident from the descriptions, tables, and keys of diagnostic characters in recent taxonomic surveys