Should the undoubted intelligence of octopuses change the way we treat them? This question has been asked a lot of late because of the documentary My Octopus Teacher.

The film is about a year-long relationship between a man and an octopus, and it takes place in a kelp bed off South Africa. It celebrates the sensitivity, awareness and intelligence of the octopus.

That’s a difficult concept. Octopuses — octopi is wrong because it’s not Latin and octopodes is insufferably pedantic — are mollusks. That’s the same phylum as slugs and snails and cockles and mussels. In other words, intelligence is not restricted to our own phylum of chordates or back-boned animals. As flight independently evolved in birds, bats, insects and the extinct pterosaurs, so intelligence has evolved independently in at least two phyla. It’s not all about us.

There are more than 300 species of octopus. The giant Pacific octopus has a leg-span of 14 feet while the star-sucker pygmy octopus has one of an inch. They have the highest brain-to-body ratio of all invertebrates. Their nervous system gives limited autonomy to their eight arms: in other words, they are intelligent in a way that lies beyond easy imagining.

Octopuses have adapted to live in several different ways: as bottom-dwellers, free-swimmers and coral-reef lurkers. They are predators: their eight arms surround a mouth with a powerful beak and they quieten their prey with poisonous saliva. The bite of the blue-ringed octopus can be fatal to humans. They are short-lived, six years at most. The male dies a few months after mating; the female after her eggs have hatched.

Octopuses are mollusks without shells. Their shell-lessness gives them mobility and flexibility, but it also makes them vulnerable. They need intelligence to make those traits work, and it has been demonstrated in controlled conditions. It was thought until about 60 years ago that tool-use defined humanity, and octopuses have been observed using coconut shells to make homes. Here is intelligence that lies not just beyond the species barrier but beyond the phylum barrier.

Octopuses have passed all sorts of maze tests. They have excellent long- and short-term memories. They can engage in (though this is disputed) observational learning, i.e. see a useful task performed and then imitate it. They can recognize individual humans. In an experiment, one person made much of the octopus while the other teased it with a wire brush: the octopus flaunted itself for the one and hid from the other.

Anecdotal evidence of intelligence is vivid and compelling: captive octopuses routinely leave their tanks to seek company, food and sex. They climb in and out of lobster-pots to take the trapped animals for themselves. People who work with them in aquaria say that octopuses have distinct personalities; this is not sentimentality but practical animal husbandry, as anyone who has worked in a stable knows.

The evidence for octopus intelligence is so overwhelming that they are categorized as honorary vertebrates when it comes to experiments. They are the only invertebrates protected by the Animal (Scientific Procedures) Act of 1986 in Britain. That has posed a question for many people. Should you treat an octopus as you would an escargot, given they are both mollusks? Is it morally acceptable to eat octopuses?

This is the old cannibal question: at what point do you draw the line? What or who is acceptable as food? The idea of intelligence plays a significant part in this fraught area of personal and societal choice. In the developed nations of the West we don’t eat monkeys, still less apes. They’re too much like us.

If you’re intelligent enough to have a personality, you’re quite a bit like us: that’s our rough-and-ready understanding of the world. We don’t eat dogs in this country and have a horror of those who do. It’s the same with horses: in 2013, £300 million ($410 million) was wiped off the British supermarket Tesco’s share value after it was found selling burgers that contained horse meat.

Travelers to some parts of America are often disturbed to find dolphin on the menu — they don’t want to eat a mammal widely celebrated for its intelligence. But in fact it’s a local nickname for a fish otherwise known as mahi-mahi.

Commercial hunting of whales was banned in 1986, though limited whaling still continues and some countries, notably Iceland, Norway and Japan, are keen to start up again. The ban came about because of the looming extinction of many species — and because of recent discoveries about whale intelligence. The ban is a rare example of humans making a decision against their own immediate interests.

We make rather a point of denying the intelligence of the creatures that we do routinely eat: cows, sheep and chickens are usually portrayed as silly. Pigs are clearly intelligent, but they are contemptible and that makes their consumption OK. To call anyone a cow, sheep, pig or chicken is an insult. We need to despise what’s on the menu but we can’t despise intelligence, as that would be to despise ourselves.

Jeremy Bentham nailed the issue in the 18th century: ‘The question is not, Can they reason?, nor Can they talk? but, Can they suffer? Why should the law refuse its protection to any sensitive being?’

The issue of food choice is deeply personal. Emotional and ethical concerns have been changing diets over the past half–century. The octopus documentary has raised further sensibilities: can we really eat creatures that are so much like us? But the fact is that animals are not like us. They are us. We all belong to the kingdom Animalia. We have tried again and again to deny it across the millennia, but it’s unavoidable. The octopus proves that truth.

This article was originally published in The Spectator’s UK magazine. Subscribe to the US edition here.