Last update of the day: Tomorrow’s New York Times has a profile I wrote about Martin Nowak, a mathematical biologist at Harvard. Nowak uses games to understand how cooperation evolved–whether that cooperation is between people or between cells or between genes. I’ve written about Nowak in passing before–his work on language evolution turns up in my book Evolution: The Triumph of an Idea, and there’s a bit on his research on cancer evolution in an article I wrote last year for in Scientific American. But I was very curious to talk to Nowak and figure out how all these topics fit inside the head of one scientist.

If you want to read more about Nowak, he’s got pdf’s galore at his web site. Be prepared for a lot of math, though. All the equations may leave you wondering what the ethereal realm of math has to do with the blood-and-guts reality of life. And it turns out, Nowak informs me, that the annals of geek humor includes a mathematical biology joke.

A shepherd is tending his sheep, and a man comes by and says, “If I guess the correct number of your sheep, can I have one?”

The shepherd says, “Please try.”

The man looks at the flock and says “Eighty-three.”

The shepherd is completely amazed that he got the right number. The man picks up a sheep and starts to walk away.

The shepherd says, “Wait! If I guess your profession, can I have my sheep back?”

The man says, “Sure.”

The shepherd says, “You must be a mathematical biologist.”

The man says, “How did you know?”

“Because you picked up my dog.”