Show Me The Science Month Day 12

Natural selection is often much like Goldilocks - an organism's traits shouldn't be too hot or too cold; natural selection likes them just right. In other words, traits are under pressure to remain near an optimum. If they deviate too far, natural selection will not-so-gently prod things back to the center. This phenomenon is known as stabilizing selection.

Stabilizing selection has to push against another powerful evolutionary force - random drift. Much of our genetic makeup is influenced by non-adaptive processes, that is, processes that are not particularly favored or disfavored by natural selection, and which do not perform some function that improves the fitness of the organism. Selection and drift have been especially hard to tease apart when it comes to gene regulation. Related species regulate their genes in different ways, but how many of those differences are simply due to random divergence? Trevor Bedford and Daniel Hartl at Harvard University take a crack at this question in a recent paper. They use a mathematical model based on Brownian motion (the kind of random motion you see when you watch pollen grains buffeted about in a drop of water) to determine how well stabilizing selection counteracts the battering of random drift.

Show Me The Science Month Day 11

Imagine a world where the major source of human nutrition was beer. That may sound fantastic to some of you, but now imagine that, in this beer-world, there are no bottle openers and no twist-off caps. To get at the beer, you have to open the bottles with your teeth. Day in, day out, you're opening bottles with your teeth. If the world continued like this for a few thousand generations, how would the human jaw evolve into a better beer bottle opener?

2 million years ago, our ancestors lived in such a world. OK, so it didn't involve beer-bottles, but our ancestors did have to use their teeth to get at what was essentially armored but highly nutritious food - nuts and seeds.