For as long as I've been thinking about it, I've assumed that humans separated from apes on the evolutionary tree because we started eating meat. I can't tell you what it was about meat that would've caused the separation. Maybe it's because the nutrients in meat were more dense, providing more fuel in smaller packages. Maybe it's because the pursuit of meat led us to take more risks, travel farther, learn more, adapt to more environments, and eventually develop tools and weapons.

For example, the simple ability to use tools to crack open bones allowed our ancestors to eat bone marrow, one of the most concentrated sources of nutrients on the planet. Other predators could kill an animal and gnaw away the meat, but the bones they left behind -- the ones they couldn't bite open with their teeth -- were the prehistoric equivalent of a McDonald's drive-through. A couple of thigh bones from a big-ass bison could provide enough marrow to feed a family. And you can't beat the portability.

But now there's a new theory: Maybe it wasn't the meat that made us men. It might've been the potatoes:

My big point here isn't really about human evolution, about which I know little more than what I've just written. It's that starchy carbohydrates -- bread, potatoes, corn -- may not be the villains we've made them out to be in the obesity crisis. The highly processed forms of those starches can't be good for anyone, but starches themselves may have a bigger purpose than previously suspected.

Interestingly, individual humans and groups of humans have huge ranges in the number of genes responsible for producing starch-processing enzymes. Some have as few as two, others as many as 15. Scientists aren't sure why:

The upshot? The author, Nicholas Wade, speculates that humans could eventually evolve to better handle the rich foods in our modern diet.

But I see something more immediate: If anyone still believes that any one diet will work for every single person who tries it, this study gives a convincing reason to think otherwise. The possible range of responses is huge.

So the next time you see a diet like the Okinawa Program, promising that you can live a million years if you eat like subsistence farmers on a Japanese island, remember that the diet only works if you have the right genes. If your ancestors evolved to survive on mammoth meat or whale blubber, you probably won't have much luck with a diet based on rice and green tea.

Monday blog starch

• This story -- about a couple in California who performed unlicensed, illegal cosmetic surgery in their filthy home -- is disturbing on two levels. First, of course, is the fact they did such horrible things to people, scarring them for life. Second is that they had any willing customers at all. I never thought there'd be a surgical analog to the subprime-mortgage crisis, but here it is.
• Scientists think they've found the brain wiring that determines whether your politics are liberal or conservative. It's cool stuff, and it's easy to see the evolutionary reason why both types of brains exist. Sometimes it helps to have conservative brains, with their ability to block out distracting information and stay on course. And sometimes you need liberal brains, with their ability to accept complexity and ambiguity and process new information. But you never need to demonize one group or the other because of what they're wired to be.
• Here's one I should've blogged last week: Hyperactivity in kids has been linked to food coloring and preservatives. I think eventually we'll learn that every aspect of modern life -- from computers to TV to the food chain -- does something unholy to the human brain. The question is, what can we do about it?