Early twin studies of adult individuals have found a heritability of IQ between 57% and 73%, with some recent studies showing heritability for IQ as high as 80% https://en.wikipedia.org/wiki/Heritability_of_IQ
Thanks, I'll edit my comments to reflect this. Intelligence remains heritable, just not as heritable as I thought.
It has more to do with what they eat, how often they eat and their exposure to different ideas than it does their genetics, etc.
One cannot discount the role of nature in the nature vs. nurture debate. Some twin studies are quite remarkable in illustrating the significant role it plays.