From another thread:

This is the reason that a lot of guys into old-fashioned "iron age" bodybuilding go wayyyyy back in time to find their role models.
I have seen naturals with huge chests, arms, backs, certain mucles don't build easy natty like delts, traps, legs. That's normally the give away.
Do other people agree with this?
What i find is that there are some muscles that will not (generally) have any decent size at all unless they are trained. There are plenty of people who do not lift weights who have enormous calves, but very few people who do not lift weights who have huge traps, for example. In my experience, anyway.