'Abdu'l-Baha says:-- The Prophets acknowledge that education hath a great effect upon the human race, but They declare that minds and comprehensions are originally different.

We see that certain children of the same age, nativity and race, nay, from the same household, under the tutorship of the same teacher, differ in minds and comprehensions.
No matter how the shell is educated (or polished) it can never become the radiant pearl.

The black stone will not become the world-illuminating gem.

The thorny cactus can never by training and development become the blessed tree.

That is to say, training doth not change the essential nature of the human gem, but it produceth a marvelous effect.