"The human brain is a thought machine" is one of the truest scientific truisms you can utter about human beings, right up there with "the heart is a blood pump," or "the eye is a camera." To the best of our knowledge, all of our perceptions, emotions, deepest longings, profoundest joys and sorrows, and even (what feels like) the exercise of free will—in short, the entire contents of human experience—are caused by the brain. The fact that so many people now take this claim for granted, as if we knew it all along (we didn't), marks just how far our scientific understanding has progressed over the past couple of centuries.
Even though the idea that the brain is a thought machine is now second nature to many people, most of us are still unable to embrace it fully. For instance, roughly two-thirds of Americans continue to believe in the existence of a soul that survives death, which is hard to swallow if you're really convinced that the brain produces the entirety of human experience. Others lose their confidence in the utterly enbrained nature of human experience when they learn of the gaps that still remain in our scientific understanding of how the brain produces thought. But there's a deeper anxiety surrounding this idea, too.
This deeper fear is that a brain-based understanding of human experience will cost humanity its dignity. If there is widespread adoption of the idea that the contents of the human mind are the output of a machine, the worriers worry, won't we treat each other with less charity, tolerance, and respect than we otherwise might? And aren't we entitled to less charity, tolerance, and respect ourselves?
No, we won't; and no, we're not.
First of all, let's keep something in mind: You don't need to believe that the brain is a thought machine to deprive humans and other sentient creatures of dignity. History shows that belief in a non-material basis for human experience can exist side-by-side quite comfortably with indifference and cruelty. Human sacrifices, witch hunts, inquisitions, and suicide martyrdom, for instance, are all premised on the doctrine that mind and body are independent entities. Indeed, people throughout history have been willing to impose horrific pain on others' (or their own) physical bodies in order to improve the condition of their non-physical souls. And could scientists have tolerated live animal vivisection for as long as they did without the moral cover they received from the Cartesian belief that body (which non-human animals obviously possess) and soul (which, according to the Cartesians, they don't) are different things? I doubt it.
But more centrally, it's just not true that human dignity is threatened by a modern understanding of the mind. What matters from a moral point of view is not whether your desires, hopes, and fears are produced by a machine, or by a huge invisible bird, or by a puff of fairy dust: The only morally relevant fact is that those aspirations are there, inside of you; the rest of us must decide whether morality is better served by making it easier for you to fulfill those aspirations, or harder. Here, there's an interesting analogy to one of the ethical questions surrounding human cloning: Would the human beings produced through cloning be entitled to the same rights as human beings produced the old fashioned way? Of course they would. What's morally relevant is not how a human being comes into the world, but simply that the person is in the world, and is outfitted with appetites, aspirations, and fears just like everybody else is. The only moral decision facing the rest of us is whether to help or to hinder that person's pursuit of fulfillment.
Not only does the conviction that the brain is responsible for all of human experience not threaten human dignity; I believe it can actually increase it. When I recognize that you and I share essentially the same thought machines within our heads (courtesy of natural selection, of course), I only need to take one small leap to come to an important moral discovery: You probably love some of the same things I love (food, family, a warm bed, liberty) and probably feel pain in response to the some of same things that cause me pain (torture, the death of a loved one, watching my children become someone else's slaves). Once I have realized that my aspirations and your aspirations are roughly the same, it's harder for me to convince myself that I'm entitled to run roughshod over your aspirations while insisting that you respect mine. Recognizing that our thought machines produce more or less the same aspirations in all of us, therefore, provides a naturalistic foundation for asserting universal human rights. We don't have to argue, as America's founding fathers did, that the universal equality of all humans is self-evident: Science has made this truth evident.
But why stop with humans? Once you realize that brains are thought machines, you might also lose your ability to impose suffering on non-human animals with impunity. After all, other vertebrates' thought machines are not so different from ours, and their thought machines cause them to love certain things, fear others, and respond to pain just as ours do. With these facts in hand, what moral justification survives for depriving non-human animals of their dignity just because they can't speak up to defend it for themselves?
We'd all like to be treated with dignity by every single person we ever meet, but it has been difficult to find a universally valid argument that enables us to insist on it. Recognizing that our brains are thought machines, designed by natural selection, can get us a little closer to the argument we want because it shows that in the most important ways, we demonstrably are all the same. Accepting this discovery does nothing to strip humanity of its dignity; to the contrary, it can lead us toward a modern rediscovery of the golden rule.