Genetic drift: the coalescent
I've warned you before that population geneticists tend to think about the world backwards. This week you'll see a very good example of that - the coalescent. Unlike everything we've talked about so far where we are trying to say something about where a population will be in the future based on the processes that are affecting it now, with the coalescent we look back in history. We try to say something about the history of the alleles in our sample. Doing so will, I hope, solidify your understanding of how genetic drift works. It also turns out that using the coalescent allows us to simulate samples much more quickly than with the process we've used before. This will become very important in a few weeks when we get to the discussion of phylogeography.