Can we justify killing animals for food?
Four philosophers have shared their views on the morality of eating meat.
Speaking to BBC Radio 4, the panel weighed in on whether or not it's right to kill animals and if Western society could ever change its views.
Here are their thoughts:
"Our future selves will consider meat eating to be barbaric"
- Peter Singer, professor of bioethics at Princeton University and the author of Animal Liberation, considered the founding philosophical statement on animal treatment.
Singer suggests one argument against eating meat is to say that if you kill a cow "you're depriving it of the rest of its existence, which could also have been a happy, good existence, so why deprive it of that just because you want to eat some meat when you've got other healthy, nutritious, delicious things that you could also eat?"
Singer, who hasn't eaten meat since 1971, counters this with the notion that this cow might not have existed at all were it not for the planning of those who wanted to eventually eat or sell its meat.
"So in a sense the cow could thank us for her existence - at least she has some existence rather than none."
He argues if this cow is killed, it means it could make way for another cow to come into existence, who would have a good life.
"So yes, this cow standing in front of us will lose the rest of her life, but that loss is replaced by bringing the other cow into existence and the other cow will also have that happy life."
He says given that our animal food supply is mostly cattle and sheep, and they are major producers of greenhouse gases, "I think on balance, it would be better if they didn't exist.
"I think we'll come to view [eating meat] in the way we now look back on the Roman games; having crowds of enthusiastic people cheering on the lions as they slaughtered the Christians or gladiators fighting each other to the death."
"A moral mistake but not morally wrong"
- Elizabeth Harman, associate professor of philosophy in human values at Princeton University.
Harman, who still eats meat but is "torn" about how she feels about it, argues that animals have moral status and that needs to be considered.
"The kind of moral picture that I would urge is one in which we think about whether we can justify our treatment of individuals. If you're going to do something terrible to a particular morally significant individual, how can that be justified?"
She explains that animal suffering matters because it's "a harm to something that counts morally."
She says by killing an animal, it is obviously harmed, and the action of this deprives it of future life.
"One way of thinking about how to justify an action is what could you say to the one that you're harming? That works very well with people."
Imagine someone as a representative of an animal and what you might say to that representative to justify your treatment, Harman says.
Arguing that if you kill a cow then create another doesn't justify killing the one cow at all, she says.
"I think that meat production is morally wrong, and I think that eating meat is a moral mistake but not morally wrong"
"Cows can learn - and know they're doing so"
- Gary Comstock, professor of philosophy at North Carolina State University.
Comstock expresses interest in whether cattle can look forward. ""In killing an animal we deprive it of its ability to have a future and to satisfy its desires."
"An interesting experiment was done by Donald Broom and colleagues at Cambridge a few years ago with heifers - one-year-old cows - which seems to show not only that they can learn, but that they take satisfaction in knowing that they are learning," he says.
In a control group, cows learned to hit a button allowing them access to a long chute with a reward at the end.
"As they learned which button to push to open the gate, they got better at pushing the right button, and the gate opened faster so they got the reward more quickly."
When they registered improvements in performance, "they jumped and kicked and galloped down to get the reward, behaviours that suggest strongly that they not only anticipated the pleasure of the coming reward, but were also taking pleasure in their own role in making it happen."
While Comstock said there is a danger of over-interpreting an animal's behaviour, these were controlled experiments. In addition, there is also anatomical evidence that should be considered.
"If you look at the brains and neural pathways in cattle, and compare them to humans, there are massive similarities. The amygdala, the cerebellum, the thalamus which are all involved in processing pain in us, are all found in cattle."
He says the justification of eating animals has shifted.
"People used to justify eating meat for biological reasons: we are omnivores, our incisors are designed to eat meat, this is a natural thing for us to do."
The issue, argues Comstock, is there are a lot of natural things that are not right for us to do, and the biological features are irrelevant to the question of how we ought to live our lives.
"Evidence seems to be building that the shoe's on the other foot now; that those who want to kill animals and eat them ought to justify their view. It shouldn't be the other way round."
"Cows have a moral interest in continuing to live"
- Jeff MacMahan, White's Professor of Moral Philosophy at the University of Oxford.
"If you didn't kill the cow, it could go on living and have a life that would be good for it. That's part of why it would be wrong for me to kill you," says MacMahan. "It would be depriving you of the good experiences that you would have if I didn't."
An animal has an interest in living to its next meal, he argues.
"You don't have to think about humans in exactly the same way that you think about cows. But you've got to explain why you think it's permissible to do to an animal what you think it would be impermissible to do to a human being."
Asked if he thinks it's permissible to kill a cow painlessly and eat it once it's had a decent life, he says if there was no other alternative for adequate nutrition, this would be okay.
But in contemporary Western societies, his inclination was to say no.
"It's not at all clear that the interest that people have in killing and eating the cow outweighs the interests that the cow has in continuing to live."