Understanding the history of species is critical to understanding evolutionary processes and for making predictions about how biodiversity will fare in a rapidly changing climate. Information about how species are related (phylogeny) and how their populations have responded to past climate change (historical demography) can inform us about the conditions under which they have evolved and adapted, and how they might respond to changes currently under way.
Modern scientists get at these questions by examining two types of data: the fossil record and patterns of DNA sequence variation. The fossil record is relatively straightforward. You find a fossil in location X. You identify it as species Y and you use some method to (e.g. radiocarbon dating) to infer it was there at time Z. Making inferences from DNA sequence variation, by contrast, involves complex, computer-intensive statistical analyses, and the field is in a state of tumultuous, rapid advance.
A fascinating case study that involves the integration of fossils and DNA sequence data, and illustrates the ways in which rapid statistical advances are changing our understanding of species’ evolutionary histories is that of the origin of the polar bear (Ursus maritimus).