haiya
issit development psych? 
okie example:
everyone has intelligence.
but how come some pple can get 50% other get 90% of the marks in a
test, though its e same method of heritability of intelligence from
parents?
cos of variation of trait: the difference in marks is due to 60% of
ur parents traits..
the rest of the 40% comes from the envirnoment...
