Many people think that genetic engineering will change everything, even our very bodies and minds. It will, eventually. Right now, however, attempts to apply new genetic knowledge are having profound effects, not on our bodies, but on how we understand our bodies. They are revealing that our central metaphor for the body is fundamentally flawed. The body is not a machine. It is something very different, a soma shaped by selection with systems unlike anything an engineer would design. Replacing the machine metaphor with a more biological view of the body will change biology in fundamental ways.
The transition will be difficult because the metaphor of body as machine has served us well. It sped escape from vitalism, and encouraged analyses of the body's components, connections, and functions, as if they were the creations of some extraordinarily clever cosmic engineer. It has yielded explanations with boxes and arrows, as if the parts are components of an efficient device. Thanks to the metaphor of the body as machine, vitalism has been replaced by an incredible understanding of the body's mechanisms.
Now, however, genetic advances are revealing the metaphor's limitations. For instance, a decade ago it was reasonable to think we would find the genes that cause bipolar disease. New data has dashed these hopes. Bipolar disease is not caused by consistent genetic variations with large effects. Instead, it may arise from a many different mutations, or from the interacting tiny effects of dozens of genes.
We like to think of genes as information quanta whose proteins serve specific functions. However, many regulate the expression of other genes that regulate developmental pathways that are regulated by environmental factors that are detected by yet other bodily systems unlike those in any machine. Even the word "regulate" implies coherent planning, when the reality is systems that work, one way or another, by mechanisms sometimes so entangled we cannot fully describe them. We can identify the main players, insulin and glucagon in glucose regulation, the amygdala in responding to treats and losses. But the details? Dozens of genes, hormones and neural pathways influence each other in interactions that defy description, even while they do what needs to be done. We have assumed, following the metaphor of the machine, that the body is extremely complex. We have yet to acknowledge that some evolved systems may be indescribably complex.
Indescribable complexity implies nothing supernatural. Bodies and their origins are purely physical. It also has nothing to do with so-called irreducible complexity, that last bastion of creationists desperate to avoid the reality of unintelligent design. Indescribable complexity does, however, confront us with the inadequacy of models built to suit our human preferences for discrete categories, specific functions, and one directional causal arrows. Worse than merely inadequate, attempts to describe the body as a machine foster inaccurate oversimplifications. Some bodily systems cannot be described in terms simple enough to be satisfying; others may not be described adequately even by the most complex models we can imagine.
This does not mean we should throw up our hands. Moving to a more fully evolutionary view of organisms will improve our understanding. The foundation is recognizing that the body is not a machine. I like to imagine the body as Rube-Goldberg device, modified by generations of blind tinkers, with indistinctly separate parts connected, not by a few strings and pulley, but by myriads of mechanisms interacting in ways that no engineer would tolerate, or even imagine. But even this metaphor is flawed. A body is a body is a body. As we come to recognize that bodies are bodies, not machines, everything will change.