My brother Ben is now a respectable consultant for the Oxford English Dictionary, but when he was a kid, he was a puzzle freak, pure and simple. In fourth grade he'd spend hours paging through a big unabridged Webster's, looking for obscure words that he could use to create a fiendish rebus. Little did I know that one day one of his favorite puzzles--the doublet--would become useful to me in thinking about evolution.
The challenge of a doublet is to turn one word into another. You are allowed to change one letter at a time, but each change must produce a real word. Here's a doublet that suits a post on evolution: Change APE to MAN.
Give up?
APE
APT
OPT
OAT
MAT
MAN
Now imagine that having solved the APE-to-MAN puzzle, you tell a friend about your triumph.
Your friend scoffs. "That's ridiculous," he says. "I don't believe you've ...
