A biologist explores a big question in evolution: does it happen the same way each time?

The scientist and writer Stephen Jay Gould famously claimed that if you “replay the tape of life” and started all over again, the end result would be very different. In other words, he argued that evolution wasn’t preprogrammed; rather, it depended on the environment and circumstances.
As a child, Jonathan Losos was swayed by this argument. But as an adult and evolutionary biologist, his own research seemed to argue against the claim that evolution is wholly contingent. In Imp