More than 10,000 years ago, when the last ice age was stumbling through its final years, both humans and viciously sharp climate change converged on North America just as three-quarters of the continent's biggest beasts disappeared forever. Both human hunters and wrenching climate shocks seemed to have the opportunity to cause extinction. But researchers have never been able to disentangle the lingering traces of humans, climate, and megafauna in enough detail to say who or what did in the great ice age beasts of North America. Now a group of paleoecologists has followed all three players through time, clearing one suspect of megafaunal mayhem and indicting another.