That's not true at all, genetics only play a part in the mental development of a person, much of it is instead related to the environment where a person has been growing.
It is as with talent, some people are better than other at certain activities but even the most gifted person cannot compete with a professional who has spent his life training and studying his craft.
The same can be said for "intelligence": if you are never taught to think you'll never think once in your lifetime, even if you are the exact copy of Leonardo da Vinci; on the other hand, even if you are thick as a rock but you've been growing in a society focused on your development you'll be able to become a normal person.
Eugenetic politics do nothing for humanity betterment, social structure is much more important IMHO