In another thread with same name a very good discussion has been there and explanation offered by Sanatan Dharma is really very valuable.

Is it only to be seen from Biological PoV ?
Or we should also see it as a continuum and connected to the "permanent state" ?
In case it is biological, which is more relevant to the gross body, where as the intellect belongs to the subtle world, is it possible to replace head of any person with Einstein's head and we will get another Einstein ?
If no then, the question comes to mind that what contributes to the intellect component ?
Is the "permanent state" connected with us at gross and subtle levels through the 5 elements ?
If so which all elements connect us for the subtle elements ? Is light one source for transmission and evolvement of intellect ? Is exposure to sunlight has any impact ? Does entry of sunlight through eyes have any impact ?
These are questions presently pushing my mind. Look forward to your insights in these areas

However, can we give a simpler explanation to whatever has been asked for by OP in the heading ? I have opened this thread to avoid derailing strings of thoughts being offered by Sanatan Dharma in another thread. Here we may have different point of views. I will explain the following post how I see this. Other members are requested to offer their valuable inputs.