34 EVOLUTION AND DISEASE. 
particular trades, as those of watchmakers, jewellers, 
ivory carvers, &c., or the precision of artists and sculp- 
tors, and, in a more marked sense, the keen ear of 
musicians, and the wonderful faculty displayed by 
mathematicians in their marvellous dealings with num- 
bers and calculations, have all been slowly attained by 
the persistent transmission of the effects of increased 
use. 
