2017-04-16 23:16:46 UTC
One more time
Let’s say upfront that asking “if humans/apes evolved from monkeys, why are there still monkeys?” is exactly the same as saying “if there are snakes, why are there still lizards?”, “if there are tetrapods, why are there still fish”, or “if there are European Americans, why are there still Europeans?”. The point that stubborn creationists apparently refuse to appreciate is that only one group among the animals that we call ‘monkeys’ evolved into the animals that we call ‘apes’: other ancestral monkeys begat more monkeys, and apes are, in fact, merely one monkey lineage among several. Yes, you should think of apes as big, weird monkeys. We just use a different name for that lineage of big weird monkeys because we find this distinction a useful one. This distinction would be less obvious if early, monkey-like members of the ape lineage still existed. But they don’t; they’re extinct. So you should think of apes as monkeys in the same way that birds are dinosaurs, snakes are lizards, and humans are apes.
The shape of the tree. Let’s look at all of this within the context of primate evolutionary history. First of all, some key terms. Monkeys and apes together – the so-called ‘higher primates’ – constitute Anthropoidea. Within Anthropoidea, Old World monkeys and apes form Catarrhini, the sister-group to Platyrrhini (the New World monkeys). Within Catarrhini, the ape lineage is Hominoidea, and the Old World monkey lineage is Cercopithecoidea. The adjacent labelled cladogram should help you out.
In recent years several new fossil anthropoids have been described that appear close to various of the key branching points in anthropoid phylogeny. Catopithecus from the Upper Eocene of Egypt is a stem-catarrhine close to the platyrrhine-catarrhine split, Saadanius from the Oligocene of Saudi Arabia must have been very close to the ancestry of the catarrhine clade that includes both apes as well as Old World monkeys, Nsungwepithecus appears to be a stem-member of the cercopithecoid clade, while Victoriapithecus from the Miocene of Kenya is an early Old World monkey outside the clade that includes colobines and cercopithecines.
Many other fossil taxa have been identified as stem-members of Anthropoidea, Catarrhini and Cercopithecoidea. In addition, several completely extinct anthropoid lineages existed during the Oligocene and Miocene, including the pliopithecoids and dendropithecids.
Because the monkeys we evolved from did not all die the instant that some of them evolved.
You, and all your friends, are monkeys. Because all of the fossil primates just mentioned fall somewhere on the tree between platyrrhines and Old World monkeys, all can be regarded as ‘fossil monkeys’, even though none of the taxa or groups I’ve just mentioned are members of modern lineages. And if we were to see any of these animals in life we would regard them as ‘monkeys’ with little hesitation.
My point here is that it’s clear that the term ‘monkey’ does not only apply to the members of two specific living anthropoid clades – Platyrrhini and Cercopithecoidea, respectively – it’s also a catch-all label for primates of a certain evolutionary grade: for ‘non-hominoid anthropoids’. But from an evolutionary, tree-based perspective, hominoids are just one monkey lineage among many. We humans, and all our other hominoid cousins, are – as I already said above – big, tail-less, bipedal monkeys. This concept might be familiar if you’re a regular Tet Zoo reader. And, look, there’s even merchandise…