Science is finally beginning to embrace animals who were, for a long time, considered second-class citizens.

    As Annie Potts of Canterbury University has noted, chickens distinguish among one hundred chicken faces and recognize familiar individuals even after months of separation. When given problems to solve, they reason: hens trained to pick colored buttons sometimes choose to give up an immediate food reward for a slightly later (and better) one. Healthy hens may aid friends, and mourn when those friend die.

    Pigs respond meaningful to human symbols. When a research team led by Candace Croney at Penn State University carried wooden blocks marked with X and O symbols around pigs, only the O carriers offered food to the animals. The pigs soon ignored the X carriers in favor of the O's. Then the team switched from real-life objects to T-shirts printed with X or O symbols. Still, the pigs walked only toward the O-shirted people: they had transferred their knowledge to a two-dimensional format, a not inconsiderable feat of reasoning.

    I've been guilty of prejudiced expectations, myself. At the start of my career almost four decades ago, I was firmly convinced that monkeys and apes out-think and out-feel other animals. They're other primates(灵长目动物), after all, animals from our own mammalian(哺乳动物的) class. Fairly soon, I came to see that along with our closest living relatives, whales too are masters of cultural learning, and elephants express profound joy and mourning with their social companions. Long-term studies in the wild on these mammals helped to fuel a viewpoint shift in our society: the public no longer so easily accepts monkeys made to undergo painful procedure kin laboratories, elephants forced to perform in circuses, and dolphins kept in small tanks at theme parks.

    Over time, though, as I began to broaden out even further and explore the inner lives of fish, chickens, pigs, goats, and cows, I started to wonder: Will the new science of "food animals" bring an ethical (伦理的) revolution in terms of who we eat? In other words, will our ethics start to catch up with the development of our science?

    Animal activists are already there, of course, committed to not eating these animals. But what about the rest of us? Can paying attention to the thinking and feeling of these animals lead us to make changes in who we eat?