This month's Secret Science Club lecture was by formerly mohawked (now shave-pated like myself) Evolutionary Anthropologist Todd Disotell, of NYU's Center for Human Origins. The topic of the lecture was applying the concept of the molecular clock to determine the approximate times of divergence within the primate clade. The "molecular clock" is typically calibrated using evidence from the fossil record.
Molecular dating techniques determine the the chimpanzee ancestor/human ancestor split occurred 5.4 to 6.3 million years ago, but that the initial divergence was followed by a period of hybridization.
Another topic that came up was the probability that the primates have a Cretaceous origin, so our oldest primate ancestors had to evade predaceous theropods (but nothing like this ever happened).
Sorry about the somewhat half-assed recap... work has gotten in the way of posting. To make up for my lackluster post, I'll try to make it up to you by posting a video of Dr Disotell in all his mohawked glory: