| Abstract: |
Darwin's phrase, "descent with modification," identifies the two core historical processes in evolution: characteristics are transmitted from generation to generation but not faithfully. The natural selection of genes is a major "modifier," but the frequency of traits may also change due to mutation, genetic drift, and gene flow. Analogous but not identical processes also shape the histories of languages and cultures. Current distribution of genetic traits, then, may reflect the interaction of both processes, descent and modification. Although called "markers," alleles do not necessarily label populations through time. Since multiple mechanisms cause allele frequency distributions, as well as linguistic and cultural traits, several hypotheses must always be considered to explain any observed bio-cultural-linguistic pattern. Recent genetic studies of global human variation have emphasized "descent," constructing tree diagrams purporting to show the history of human populations. These models are based on a branching process of genetic divergence, with population splits followed by isolation and gene drift providing the evolutionary dynamic. On the other hand, numerous studies of the population structures of small-scale human groups have found that networks of mobile individuals (foragers) or interlinked village clusters (farmers) are common. These studies imply that reticulate, anastomosing population histories provide a better model for human genetic history than do phylogenetic tree diagrams. Recent reconstructions of the linguistic and cultural prehistory of the Malaysian peninsula along with contemporary surveys of biological variation can be used to assess a branching evolutionary model of fissioning and population replacement versus a mosaic model of long-term population interaction and gene flow.
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