 What seems to be the core idea behind the specialist segregation?
From the born mechanic and the man with the gift of gab, society evolved to the point of smaller contact and less communication between the specializations, until now they could understand each other on only the most basic physical necessities—and not even always then. The ultimate should be the complete segregation of each specialization—social and genetic measures to make them breed true, because the unspecialized man is an uncivilized man, or at any rate he does not advance civilization. And letting the specializations mix would produce genetic undesirables: clerk-laborer or Professional-GI misfits, for example, being only half specialized, would be good at no specialization. And the basis of this specialization society was: "The aptitude groups are the true races of mankind."
 To make humanity work at it's prime, with everyone working at maximum capacity.
 To create a class system and with it a hierarchy.  To make humanity work at it's prime, with everyone working at maximum capacity.  To provide a means where people are at their happiest, working where they "should."  People are uncappable of carrying out more than one job, and the specialist segregation allows them to focus on just one.