[gbjw]

“ Intelligence is one of the greatest human gifts. But all too often a search for knowledge drives out the search for love. This is something else I've discovered for myself very recently. I present it to you as a hypothesis: Intelligence without the ability to give and receive affection leads to mental and moral breakdown, to neurosis, and possibly even psychosis. And I say that the mind absorbed in and involved in itself as a self-centered end, to the exclusion of human relationships, can only lead to violence and pain.” - Daniel Keyes, Flowers for Algernon

[strken]

You can remove intelligence from that hypothesis entirely, and it won't change the meaning. You can substitute almost anything else, too: "Owning a rubber duck without the ability to give and receive affection leads to mental and moral breakdown, to neurosis, and possibly even psychosis." Well, yeah, but why is the duck in that sentence?

[Antibabelic]

It's in there because of the claim directly preceding it: "But all too often a search for a rubber duck drives out the search for love". It builds upon that first statement.