I had read this before, but so long ago (early teens?) that I couldn't really remember it. I've liked other stories by WIlhelm, so decided to re-read. Starts off with a nicely promising apocalypse, but quickly becomes a story of oh-no-the-clones! They're not Human!
The (very thin) scientific premise is that individuality must be developed at an early age, and if a group of clones grows and develops together, they will fail to develop individuality (and associated traits like creativity, imagination, the ability to fall in love, the possibility of genius, etc). The clones think they are awesome and aim to create a safe, communal society. Only a couple of people see the deadly trap the remnants of humanity are falling into.
Not only is there no logical reason that clones would develop the traits that Wilhelm gives them, the book's message about the importance of creativity and individuality seems like a straw man argument. Would anyone seriously argue that the ability to innovate is NOT important? Maybe there's a bit of a cold-war era residual paranoia about communism that contributed to this; I'm not sure.
The "happy" ending of the book is also problematic. OK, the one 'individual' man kidnaps a harem of fertile women and sets out to repopulate the earth with hardworking innovators. Hmm. Are we concerned about genetic diversity, anyone? The numbers of individuals required for a viable population? Nah, everything'll be fine. (I'm fairly certain that people did know about the problems associated with extreme inbreeding even in 1976.)
I have to admit that I still found the book enjoyable - I just like this sort of apocalyptic novel. But it's definitely flawed.