US A Geneti c an d environmen ta l in uence s on behaviou r an d developm en t ca n be examine d by studyin g mor e tha n on e individua l withi n a family

usin g quantitativ e geneti c theor y an d behaviour al geneti c (BG ) methodolog y. Speci Ž c environmen ta l an d geneti c in uence s ca n be measure d an d effec t size s estimated