Do canine teeth mean humans should eat meat?

The objection

“Humans have canine teeth, the pointed teeth that evolved for tearing flesh. If nature gave us the tools of a meat-eater, surely using them is natural and appropriate.”

The answer

Humans are omnivores, as the answer on whether humans are omnivores or herbivores sets out, but our canine teeth are poor evidence for it. In apes and monkeys, canine size mainly follows rivalry between males and has little to do with diet. In our own lineage the male canine had shrunk to near the female’s size about two million years before the butchered bones that scientists usually link to early Homo, and as meat-eating rose, canines grew slightly smaller still.

What are big canines for?

Big canines in apes and monkeys are mainly weapons for fights between males [1], and the hippo, a plant-eater, uses its canines, enlarged into tusks, for display and fighting [7]. Relative to skull length and body mass, the canines of male primates are on average as large as those of similar-sized carnivores or larger, according to Plavcan and Ruff (2008), who call their role as weapons the consensus view and also found that seed-eating primates have relatively strong canines [1]. Comparing anthropoid primates, the group of apes and monkeys, Plavcan and van Schaik (1992) found the size gap between male and female canines very strongly linked to competition between males, and also wider in savanna-dwelling species, which they put down to predation, while diet played no role [2]. Plavcan’s 1993 study of male canines found that neither their size nor their shape generally varied with diet [3].

Gorillas show the pattern clearly. Measured across the base of the crown, a male gorilla’s canines are about 1.4 to 1.5 times the size of a female’s, the biggest difference of any living great ape (Suwa et al., 2021) [4], though male and female western gorillas eat much the same food (Doran-Sheehy et al., 2009) [5]. Their diet is almost entirely plants: in a 2021 study of Grauer’s gorillas in a low-elevation forest in the Democratic Republic of the Congo, fewer than 1% of 10,514 feeding signs were on ants, termites or fungi [6]. In carnivores, the canine is generally a cone for puncturing and gripping [4], and its size and shape go with the way each species kills [1].

Why are human canines so small?

Human canines are small because the male canine shrank to near the female’s size early in our evolution, and canines in general became smaller still later on. A 2021 study of the fossils links the first change to less aggression between males. Among all apes and monkeys, humans have proportionately the smallest male canines, with little difference between the sexes [4]. In Ardipithecus ramidus, about 4.5 million years ago, male canines were on average only 6% to 13% larger than females’, within the range of people today, according to Suwa and colleagues (2021) [4]. The few canines known from 5 to 7 million years ago fall within the same size range, which the authors say strongly suggests that the male canine had already shrunk in the earliest known members of our lineage, and they read the pattern as a profound change in behaviour, towards comparatively weak male aggression [4]. Canines as a whole were still bigger than ours: in the species before Australopithecus the crowns appear to have averaged about 30% larger than in people today, and in Homo, after about 2.5 million years ago, they shrank slightly further [4].

Eating more meat came later. Cut-marked and percussion-marked bones, which the Smithsonian calls direct evidence of meat and marrow eating, go back 2.6 million years, and scientists usually associate them with the first appearance of Homo [9]. Even Ben-Dor and colleagues (2021), who argue that our ancestors rose to a high, carnivorous place in the food chain, date the climb to the Pleistocene, beginning with Homo habilis [8]. By the time of the oldest of those bones, the male canine had been near the female’s size for about two million years, and the slight shrinking of canines in Homo came as meat-eating rose [4].

Would meat-eating teeth make eating meat right?

Teeth built for meat would not make eating it right, because being able to do something is not, by itself, a reason to do it. Our hands are capable of violence, which has never made violence permissible, and someone born with unusually large canines would be no more entitled to harm others than anyone else; we use reason to override what our bodies could do precisely because we can weigh the cost to others. Nor, for most people, is meat a need. In the UK, the British Dietetic Association says you can get all essential nutrients from plant foods, though vegans need a reliable source of vitamin B12, and that carefully planned plant-based diets can support healthy living at every age and life stage [10].