While it is sometimes useful to say something like genetic variation explains 50% of the variance in trait X, this may often be misleading because of how genes interact with the environment and with each other.
A trait may be immutable at age ten or twenty which was very much undetermined at age two.
Not to mention that heredity is always defined relative to a specific population being measured.
(For instance, giving everybody in a certain area access to high-quality education will reduce environmental variation and thus increase the role that genetic variation plays, pushing up the measured heredity of educational achievement.)
While it is sometimes useful to say something like genetic variation explains 50% of the variance in trait X, this may often be misleading because of how genes interact with the environment and with each other.
A trait may be immutable at age ten or twenty which was very much undetermined at age two.
Not to mention that heredity is always defined relative to a specific population being measured.
(For instance, giving everybody in a certain area access to high-quality education will reduce environmental variation and thus increase the role that genetic variation plays, pushing up the measured heredity of educational achievement.)