gray matter of the brain basically is hereditary, the main factor for IQ

or i should say a topic closely related to this

however the white matter also plays crucial role. the development of this part of brain is closely related to education, the younger started, the more prominent difference it causes

so if identical twins are separated and educated differently as early as different, their brain development (white matter part especially) could be quite different. their IQ and other talent/skill measurements could have striking difference