An expert is one who knows more and more about less and less.
- Nicholas Butler
Take THAT Adam Smith!
Mild sarcasm font over, there are obviously productivity gains to be had from specialisation and the division of labour. (Busy reading David Landes' "The Wealth and Poverty of Nations" at the moment... and this is certainly a recurring theme.) Still, you start running into diminishing marginal returns if your population is entirely composed of - as an old university professor of mine memorably put it - "idiot savants".