I didn't quite get the point of this story. Human experimenters have been raising colonies of monkeys & apes in an effort to make them smarter. They've figured out a way to extract some substance from a smart animal's body & inject into the dumb one - so dumb one will become smarter! There is a separate thread of curing a mentally deficient human child. And tangents about protagonist's family problems.
Fact sheet.First published: Damon Knight (Ed)'s "Orbit 3" (1968).
Note: Why is this post so short?