Meat-eating, some scientists have asserted, is what made us human.
The argument goes that if early humans did not have a diet with good amounts of animal protein, we wouldn't have the level of intelligence that we do.
Ancient hominins mainly ate fruits, plants and seeds. They spent a lot of energy on digestion and their brain remained relatively small, similar to other primates.
When early humans added meat to their diet, the human gut slowly shrunk. With less energy needed for digestion, more energy could be spent on the brain. The brain grew in size and humans became smarter.
Harvard biological anthropologist Richard Wrangham argued in his book, Catching Fire: How Cooking Made Us Human, that cooking food may have transformed ancient genes into our current human ones.
But in the current era, meat-eating is being widely challenged for ethical, health and environmental reasons.
A rising movement concerned about animal welfare, factory farming and climate change are advocating for vegan diets, or diets with much less consumption of meat.
All types of animal protein are in the sights of those seeking to end animal cruelty.
In the past, there's been a common belief that fish are less sentient and less able to suffer than other animals. But as the Herald reports, University of Newcastle marine ecologist Vincent Raoult says fish have feelings and can experience pain.
In recent times, the ethics of eating animals has become a prominent topic of discussion among deep thinkers.
Philosopher and neuroscientist Sam Harris, for example, says eating meat can't be ethically defended.
"It's unethical to delegate something that you wouldn't do yourself. If you'd be horrified to kill an animal to get your next hamburger, well then to have it done out of sight and out of mind is not an ethical solution," Harris said.
Evolutionary biologist Richard Dawkins has compared eating meat to slavery.
Dawkins eats meat but would like to be a vegetarian.
"In 100 or 200 years time, we may look back on the way we treated animals as something like we look back today on the way our forefathers treated slaves," he said.
The health benefits of diets with and without meat are also being hotly debated. Extreme positions aside, many nutritionists advocate for eating less red meat in particular.
Climate advocates are also pushing for much less meat production to reduce carbon emissions.
The United Nations says including more "coarse grains, legumes, fruits and vegetables" in people's diets could help the world limit and adapt to climate change.
As these debates continue, consumption of animal protein seems set to remain on the table as something that requires change.
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