Cows, for example, are very intelligent. They worry over what they don't understand and have been shown to experience "eureka" moments when they solve a puzzle, such as when they figure out how to open a particularly difficult gate. Cows communicate by staring, and it's likely that we don't fully understand their very subtle forms of communication. They also form close and enduring relationships with family members and friends and don't like to have their families and social networks disrupted. Chickens are also emotional beings, and detailed scientific research has shown that they empathize with the pain of other chickens.

Raising happy animals just so that they can be killed is really an egregious double cross. The "raise them, love them, and then kill them" line of reasoning doesn't have a meaningful ring of compassion. And this isn't mercy killing (euthanasia) performed because these animals need to be put out of their pain. No, these healthy and happy animals are slaughtered, and if you dare to look into their eyes, you know that they're suffering. If you wouldn't treat a dog like this, then you shouldn't treat a cow, a pig, or any other animal in this way.

As a field biologist who studies animal behavior, I feel that the authors' appeal to what happens in the natural world -- "life feeds on life" -- is an illogical justification for their food choices. I've seen thousands of predatory encounters. I cringe when I see them, but I would never interfere. Wild predators, unlike us, have no choice about whom or what they eat. They couldn't survive if they didn't eat other animals. And indeed, many animals are vegetarians, including non-human primates, who eat other animals only on very rare occasions.

Jessica Pierce and I wrote about how appeals to nature are misleading and illogical in our book Wild Justice: The Moral Lives of Animals. We argued that wolves, lions, and cougars, for example, are not moral agents and can't be held accountable for their actions. They don't know right from wrong. On the other hand, most humans do know what they're doing and are responsible for their choices. When it comes down to whose flesh winds up in our mouths, we can make choices, and in my view, eating animals is wrong and unnecessary, even when they are "humanely" raised and slaughtered. Let me add a caveat here because, as a world traveler, I do know that many people do not have the luxury of making a choice about their meals and must eat whatever is available to them. However, those who do have that luxury can easily eat an animal-free diet. And we can work to show others that a vegetarian or vegan diet can be very economical and healthy.

Niman and her friends also note that vegetarian and vegan diets have "never really taken hold." So what? This hardly means that we shouldn't try to do the right thing. They write, "The vast majority of Americans who do try vegetarianism or veganism -- about three-quarters of them -- return to eating meat. Rather than urging people to consume only plants, doesn't it make more sense to encourage them to eat an omnivorous diet that is healthy, ethical, and ecologically sound?" No, it doesn't. What it means is that these people should try harder and not give up just because it might seem difficult to change their meal plans. Perhaps they just need more time and encouragement from other vegetarians who can show them how easy it is to stop eating animals.