Evolution

Big canine teeth do not make an animal a meat eater

By WhyStopHarmingAnimals.com

"Look at your canine teeth" is one of the oldest arguments for eating meat. It falls apart as soon as you look at the animals that carry much bigger canines, and sometimes claws as well, and spend their lives eating plants.

Fangs on the grass and in the canopy

Every living primate, monkeys and apes included, has forward-facing eyes[4]. A long-standing explanation, laid out by BBC Future, is that binocular vision helps a primate judge distance while moving through trees[2]. It comes with being a primate[2][4], and most primates eat plants.

Big canines are just as common. The San Diego Zoo describes the gelada as the only grazing monkey: more than 90% of its diet is grass blades[3], yet males flash some of the largest canines in the primate world[3]. They use them as a threat display[3]. Male mountain gorillas have some of the biggest fangs among primates, and Rothman and colleagues (Biology Letters, 2011) found their diet overwhelmingly plant-based, with leaves for most of the year and fruit when it is available[4]. Males use those canines for display[4]. Brown howler monkeys in Brazil have forward-facing eyes and sizable canines[5], and in a 2016 PLOS ONE study by Chaves and colleagues most of their feeding records were fruit and leaves[5]. Colobus monkeys, often called leaf-eating monkeys, have complex stomachs that ferment a diet of leaves, flowers, fruit and seeds, according to Britannica[6]. WWF describes orangutans as mainly fruit eaters that add young leaves, flowers, insects and bark[7]. Mandrills and baboons also carry canines far larger than ours, used mainly for display and defense.

The primates that do hunt

Chimpanzees, bonobos and baboons are the species people name because they hunt, and they are worth a closer look. Wild chimpanzees are omnivorous fruit eaters; Project Chimps puts meat at less than 2% of what they eat[8], with nearly all the rest coming from plants[8]. Oelze and colleagues used stable isotopes to study bonobos at LuiKotale (PLOS ONE, 2011)[9]. Bonobos do catch small vertebrates, but the isotope signal showed that animals make only a marginal contribution to their tissue protein[9], and fruit, leaves and other plants supply the rest[9]. Hill and Dunbar compared baboon populations (Behavioral Ecology and Sociobiology, 2002) and found diets dominated by fruit, leaves and underground plant foods[10]. Animal matter was a much smaller share[10], and it did not track climate the way plant foods did[10]. Baboons take meat and insects when they can, but they do not live on them[10].

Pandas, hippos and bears

Outside the primates the pattern holds. Giant pandas descend from meat-eating carnivorans[11] and kept the group's canines[11] and claws, yet Nie and colleagues (Current Biology, 2019) describe them as specialized herbivores that feed almost exclusively on bamboo[11]. Their teeth reflect ancestry rather than diet[11]. Hippos have canines that can reach 20 inches[12], and National Geographic notes they use them for fighting[12]. They chew with their molars[12], and a hippo may eat on the order of 110 pounds of grass in a night[12].

Bears are the usual mascot for "claws and fangs mean meat", and most bears eat mostly plants. The National Wildlife Federation puts vegetation at 80 to 90 percent of an inland grizzly's intake: roots, tubers, grasses and berries[13]. The National Park Service found that grizzlies in Greater Yellowstone ate more than 162 plant species[14], and their claws, up to 10 cm long, dig roots as often as they open a carcass[14]. The bears do eat animals, but animal food is not most of what they eat[13][14]. Most of an American black bear's diet is berries, fruit, sedges and insects[15], and park interpreters routinely put plant matter near 85 to 90 percent[15]. Coastal brown bears eat more salmon because the fish runs bring it to them, which says more about the river than about what a bear's teeth are for.

What that means for us

Human canines are small and blunt, and most monkeys and apes have flat nails like ours instead of claws. Those nails do not open a hide either. If a gorilla's fangs do not make it a hunter, ours make an even weaker case. And if fangs and forward-facing eyes meant an animal was built to kill, the gelada would hunt like a wolf. It spends its days eating grass[3].