The Astonishing Hypothesis is that "You," your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. As Lewis Carroll's Alice might have phrased it: You're nothing but a pack of neurons. This hypothesis is so alien to the ideas of most people alive today that it can truly be called astonishing.
So begins Francis Crick's 1994 book "The Astonishing Hypothesis: The Scientific Search for the Soul." As a caveat lector, this is natural reductionism at its finest. Crick, as the co-discoverer of the biochemical structure of DNA, is using his international fame to convince not only fellow scientists, but the general public that life is merely an interesting combination of carbon, hydrogen, oxygen, nitrogen and a few other trace elements.
Other philosophers of science agree that we are made up of molecules, but they refuse to admit that we are nothing but a pack of neurons. These natural non-reductionists claim that the biochemical analysis of life is just one level of defining our status as living beings on this earth and specifically as humans. I have no qualms with this view. However, Crick is one of the few philosophers that I have read who goes as far as to say that life can be explained using a few simple biochemical principles.
Religious criticisms of "The Astonishing Hypothesis" focus mainly on notions of the soul and how it is separate from the body. I do not believe notions of a detached soul can be adequately reconciled with modern genetics and psychology; most devout people I have talked to cannot even explain what a soul really is. But it is not my job – nor is it anybody's – to prove the existence or nonexistence of souls. What I am interested in are the ethical implications of natural reductionism.
Besides mitochondria and some archaeobacteria, the genetic code is the same for all living things on earth. While the phenotypic differences between humans and other primates, for example, are remarkable, the actual base pair differences are very slight. Regarding our treatment of other species, what do these facts imply? At its most extreme, the fact that DNA is the genetic material for all living beings could imply two things: 1) we should treat all life as we would treat human beings, or 2) we should treat human beings as we would treat all other forms of life.
Let's look at implication No. 1. While animal rights activists would agree that we actually should treat animals as we would treat humans, I don't think that they would afford the same treatment to plants, bacteria, fungi and insects. But let's say humans could develop food and materials without killing anything – should we hold other species to the same standards as humans? When a lion kills an antelope, should we hold it liable for murder? Should we incarcerate the bacteria that infect our bodies and cause disease? Should raccoons be arrested for stealing our garbage?
That doesn't seem to work. Lets look at implication No. 2. According to this logic, we should regard human beings as just another species on this earth. Since we kill animals and plants daily, what is the difference in killing and/or eating a human being? (Jonathan Swift would be amused.) We keep some species as pets and laboratory specimens – why not create a human zoo or a human breeding colony? This theory effectively demolishes many social taboos as well, such as adultery. (President Clinton, you're off the hook!)
Obviously, there are not many people who make such outrageous claims, even in the scientific field. I would venture to guess that there is a dividing line between humans and other species – we just have to find it. Some say that language divides us, and others say that it is self-consciousness. Both of these ideas are hotly contested among linguists and primatologists, respectively. At this point, I think most people take it as self-evident that there is something unique about being human.
Maybe the answer lies in our genes. But I cry out against any attempt to reduce our humanity to mere gene expression. Humans have produced great technology, music, art, literature, sociopolitical structures and philosophies. We have found new ways to describe the universe around us and even to control it. We have even created new forms of genetic inheritance in the form of genetic engineering and cloning. With this in mind, I think it should be clear that our humanity goes way beyond our genome.