After a global economic collapse, a small group of tourists escape war-torn Ecuador on a cruise ship and become stranded on the Galapagos islands. Millions of years later their descendants are the only remaining human beings on the planet, having evolved into seal like creatures with short life spans and tiny brains.
In this novel, Vonnegut asks: "What's so great about civilization anyway? Wouldn't we all be better off as animals?" And then he tells us: "Yes. Yes, we would."
Vonnegut was never particularly subtle but the later he got in his career the more prescriptive he became.