I’ve gotten into a bit of a pissing contest which I feel I’ll share with you involving how we define terms in science and why we use taxa in common language. One of the arguments goes something like this “ape” isn’t a scientific taxon, so it’s not synonymous with the Hominoidea superfamily. Another is that “great ape” is not synonymous with the Hominidiea family. Of course, these common names can mean anything we want them to, just like any other words, and we can group organisms arbitrarily without any reference to the evolutionary relationships of these organisms. When using these terms, however, the synonymous nature of common names to scientific names is fairly well understood in the scientific literature.
Old World Monkey=Cercopithecidae
New World Monkey=Platyrrhini
Primate=Primates (this one even entered common language)
My problem with using the common names relates to some of the trickery and “gotcha” games often played by many people implying that “apes” are not Hominoidea such as in “Humans evolved from apes.”
Laden presents the argument of “how does ape (hominoid) become a family distinct from OW simian primates?”
The answer is that Hominoids are a subgroup of OW simian primates. Hominines are Hominoids AND OW simians primates. They are subgroups of subgroups of subgroups. While humans may be a subgroup of apes, we are still apes. Let’s see how simple I can make this explanation while remaining mostly accurate without using terms no one has heard of (Hominan, Hominin, etc).
All humans and ancestors of Humans to the LCA of humans and chimpanzees are termed “A” after which, they, and all of their descendants are termed “B” which includes humans and chimpanzees along with the extinct descendants of these organisms. With each included LCA with another organism, the name of the larger group changes (C, D, E, etc.) Humans are included within the “A” group, and so are included in the “E” group as well by matter of extension. Including Pan and Gorilla into any group based upon evolutionary relationships requires the inclusion of Humans. Similarly, including crocodilians and squamates as “reptiles” requires the inclusion of birds. Even though “birds” are a distinct lineage from other some other archosaurs, the inclusion of some archosaurs (crocodilians) as “reptiles” requires the taxon of reptilia to include birds since you include the LCA of crocodilians and birds.
If you include turtles and crocodiles into a clade, all squamates, along with birds, are automatically included since the LCA of birds, squamates, testudines, and crocodilians is within that group. Selectively including paraphyletic lineages of an LCA is not an evolutionarily compliant taxon. The only way “birds” are distinct from “reptiles” would be if the LCA of birds and ALL other reptiles occurred prior the LCA of all other reptiles. This is precisely what seems to have happened with testudines, allowing them to be split from squamates AND crocodilians AND birds without the group being paraphyletic.
Birds can be safely separated from crocodilians, but crocodilians and squamates cannot be separated from birds since the LCA of birds and crocodilians is more recent than the LCA of crocodilians and squamates.
In a similar light, humans can be separated from chimpanzees safely, but chimpanzees and gorillas cannot be separated from humans.
You want “monophyly”