Every year, by estimates from the UN Food and Agriculture Organization, humans slaughter more than 80 billion land animals for food, most of them chickens, along with a far larger number of fish. How those animals live, and whether people should eat them at all, is one of the oldest moral questions about food and one of the most pressing today.

From farmyard to factory

For most of history, farm animals lived on small, mixed farms, eating scraps and grazing land that could not grow crops. In the twentieth century that changed in rich countries, and it is now changing fast in poorer ones. Industrial livestock farming keeps large numbers of animals indoors at high density, feeding them grain and soy, with breeds selected for rapid growth. A modern broiler chicken reaches slaughter weight in about six weeks, far faster than the chickens of the 1950s. These methods made meat, milk and eggs much cheaper and put them within reach of far more people.

They also raised new problems. Animals in crowded indoor systems may be unable to turn around, root, nest or perch. Fast growth can leave birds with painful leg problems. Large herds produce manure in volumes that can pollute water, and the routine use of antibiotics on farms contributes to drug-resistant bacteria.

The moral arguments

The philosopher Jeremy Bentham, writing in 1789, put the central question in a single line: "The question is not, Can they reason? nor, Can they talk? but, Can they suffer?" Many modern philosophers build on that idea. Peter Singer, in his 1975 book Animal Liberation, argued that giving animals' suffering less weight simply because they belong to another species is a prejudice, which he called speciesism, using a term coined a few years earlier by Richard Ryder. Others went further. The philosopher Tom Regan held that animals have rights that forbid using them as mere resources, so that even painless farming would be wrong.

Defenders of eating meat make several arguments. Some hold that humans have a special moral status, so that animal interests, though real, count for less. Many draw a line between killing and cruelty. Welfare reformers accept the use of animals but seek to reduce their suffering, and argue that animals raised well and killed quickly can have lives worth living. Others point out that grazing animals can turn grass on steep or dry land, unfit for crops, into food; that pastoral peoples from Mongolia to East Africa depend on their herds; and that for many of the world's poor, a little meat, milk or eggs is the best source of iron, zinc and vitamin B12. Vegans need a B12 supplement or fortified foods.

The diet question

Diet choices also carry environmental weight. As the previous level noted, livestock occupy most farmland. Producing a kilogram of beef generally takes far more land and causes far more greenhouse gas emissions than producing a kilogram of beans or grain, though methods vary greatly between farms. This has led some researchers to propose diets built mostly on plants, with modest amounts of meat and dairy. In 2019 a commission convened by the medical journal The Lancet proposed such a planetary health diet. Critics asked whether it was affordable for the poor and whether it suited every culture and climate.

Technology is offering new options. Plant-based meat substitutes have spread in supermarkets. Cultivated meat is grown from animal cells in large steel tanks, without raising and slaughtering whole animals. Singapore approved the first sale of it in 2020, and the United States followed in 2023. Whether these products can become cheap enough to matter remains uncertain, and some places, such as Italy and several US states, have banned cultivated meat outright.

Laws and reforms

Laws on farm animal welfare vary widely. The European Union banned conventional battery cages for laying hens from 2012, requiring larger, furnished cages or cage-free systems. In 2018 California voters approved Proposition 12, which set space rules for hens, breeding pigs and veal calves and applies to products sold in the state wherever they were raised. The US Supreme Court upheld it in 2023. Many large food companies have pledged to buy only cage-free eggs, though progress on those pledges has been uneven.

Worked example: reading an egg carton

Imagine standing in front of a shelf of eggs with five different labels. Conventional eggs in the United States usually come from hens kept in battery cages, each bird with less floor space than a sheet of letter paper. Cage-free means hens can move around inside a barn, but not that they go outdoors. Free-range adds some access to the outdoors, though rules on how much differ. Pasture-raised usually means more outdoor space, but in the US the term is mostly defined by private certifiers rather than by law. Organic adds rules on feed and outdoor access.

Each step up costs more, and each shopper must decide how much animal welfare is worth to them. The carton also shows the limits of labels. Without knowing the rules behind each word, a shopper can pay extra for a phrase that means little. The moral question Bentham raised does not go away at the store; it just arrives in small print.