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Empathy for living members of the same species is not unheard of either. "When rats are in pain and wriggling, other rats that are watching will wriggle in parallel," says Marc Hauser, professor of psychology and anthropological biology at Harvard. "You don't need neurobiology to tell you that suggests awareness." A 2008 study by primatologist Frans de Waal and others at the Yerkes National Primate Research Center in Atlanta showed that when capuchin monkeys were offered a choice between two tokens one that would buy two slices of apple and one that would buy one slice each for them and a partner monkey they chose the generous option, provided the partner was a relative or at least familiar. The Yerkes team believes that part of the capuchins' behavior was due to a simple sense of pleasure they experience in giving, an idea consistent with studies of the human brain that reveal activity in the reward centers after subjects give to charity.
Animal-liberationist Singer believes that such evidence of noble impulses among animals is a perfectly fine argument in defense of their right to live dignified lives, but it's not a necessary one. Indeed, one of his central premises is that to the extent that humans and animals can experience their worlds, they are equals. "Similar amounts of pain are equally bad," he says, "whether felt by a human or a mouse."
Hauser takes a more nuanced view, arguing that people are possessed of what he calls humaniqueness, a suite of cognitive skills including the ability to recombine information to gain new understanding, a talent animals simply don't have. All creatures may exist on a developmental continuum, he argues, but the gap between us and the second-place finishers is so big that it shows we truly are something special. "Animals have a myopic intelligence," Hauser says. "But they never experience the aha moment that a 2-year-old child gets."
No matter what any one scientist thinks of animal cognition, nearly all agree that the way we treat domesticated animals is indefensible though in certain parts of the world, improvements are being made. The European Union's official animal-welfare policies begin with the premise that animals are sentient beings and must be treated accordingly. This includes humane conditions on farms and in vehicles during transport and proper stunning before killing in slaughterhouses.
In the U.S., food animals are overwhelmingly raised on factory farms, where cattle and pigs are jammed together by the thousands and chickens are confined in cages that barely allow them to stand. But here too, public sentiment is changing. Roughly half of vegetarians list moral concerns as the chief reason for giving up meat. Still, vegetarians as a whole make up only about 3% of the U.S. population, a figure that has barely budged since before the days of Singer's manifesto. And there are three times as many ex-vegetarians as practicing ones.
Even Singer doesn't believe we're likely to wake up in a vegan world anytime soon. For that matter, he doesn't think it's morally necessary. Eating meat to avoid starvation is all right, he believes, and some creatures are fair game all the time, provided they're grown sustainably. "I think there's very little likelihood that oysters, mussels and clams have any consciousness, so it's defensible to eat them," he says.
What's more, we're not going to quit using animals in other ways that benefit humans either testing drugs, for example. But we could surely stop using them to test cosmetics, a practice the E.U. is also moving to ban. We could surely eat less meat and treat animals better before we convert them from creature to dinner. And we could rethink zoos, marine parks and other forms of animal entertainment.
Ultimately, the same biological knob that adjusts animal consciousness up or down ought to govern how we value the way those species experience their lives. A mere ape in our world may be a scholar in its own, and the low life of any beast may be a source of deep satisfaction for the beast itself. Kanzi's glossary is full of words like noodles and sugar and candy and night, but scattered among them are also good and happy and be and tomorrow. If it's true that all those words have meaning to him, then the life he lives and by extension, those of other animals may be rich and worthy ones indeed.