and they don’t understand that there has never been a common ancestor of all and only the monkeys
This fact though—that monkeys are paraphyletic—argues in favour of (not against) the view that the common ancestor of monkeys and apes was itself monkey-like...
If you think about when the “ape traits” must have evolved, it would be after the new-world monkeys had already diverged away. The common ancestor of monkeys and apes wouldn’t have had them, but must have had those traits common to both old and new-world monkeys. It itself has to be basically a monkey.
(I drew out a phylogenetic tree for this but couldn’t get it to format, alas...)
This fact though—that monkeys are paraphyletic—argues in favour of (not against) the view that the common ancestor of monkeys and apes was itself monkey-like...
If you think about when the “ape traits” must have evolved, it would be after the new-world monkeys had already diverged away. The common ancestor of monkeys and apes wouldn’t have had them, but must have had those traits common to both old and new-world monkeys. It itself has to be basically a monkey.
(I drew out a phylogenetic tree for this but couldn’t get it to format, alas...)