Humans' closest relatives, Chimpanzees and other great apes, are mainly herbivorous (although they consume animal-based foods such as insects and small other animals.) This is a radical difference from humans, where meat makes up a large portion of many individuals' diets (not to mention a prevalence of "meat cultures" in many human societies...think the "barbecue party" in American culture.)
shareBBC Radio 4 In Our Time - Homo Erectus
https://www.bbc.co.uk/programmes/m00168lg
They eat and like meat and plants, find both very tasty I suppose.
shareChimps are our closest genetic relatives, and they will eat meat if they can get it. They aren't particularly good hunters, so they don't get much, but they'll gladly kill at eat other animals, birds, and insects. Among the great apes, bonobos will also eat meat if they can get it, but gorillas and orangutans will not.
So in genetic terms we're closely related to both omnivores and herbivores, but not pure carnivores.
Primates eat insects, fruits, nuts, roots and leaves. Our lineage diverged from that regime into, along with, an oppotunistic scavenger and ultimately predator diet. Our dentition followed. Voila. Omnivour. Neanderthals and possibly Denisovans may have converged onto something like an obligate carnivore diet due to climate & environs.
I suppose whenever our hominid or homo ancestors were eating anything they could get their hands on, the term immediately applied.
The diminished canines of hominids relative to the other apes implies, to paleontologists, that our line had a less aggressive social organization, with males either pair-bonding with females or, at any rate, not fighting over them in the manner of chimps/gorillas/orangs. Don't know about gibbons. I love gibbons.
Gibbons, at least some species, pair-bond for life. They also walk much more like us than do the knuckle-walkers. My theory is that the LCA of humans-chimps looked and walked (either in the trees or on land, samesame) a lot more like a gibbon than either a human or a chimp.