‘Everything has two handles, the one by which it may be carried, the other by which it cannot.’ –Epictetus
According to Descartes’ model, any real understanding of the body could only come from taking it apart, just as one takes apart a machine to discover its inner workings. If we wish to understand how a clock tells time, according to this model, our job is to disassemble it. Understanding a clock means understanding its springs and gears. And the same is true of living “machines.”
This notion of the body as a machine would clear away centuries of intellectual detritus: By arguing that the body was the sum of its interacting parts, and, more importantly, by suggesting that the study of those parts would reveal the workings of the body, Descartes shifted centuries of scientific and philosophical discussion about imponderable life forces and inexplicable animist vapors. (Lest we go overboard in praising Descartes, he clearly panicked at the last moment. He exempted human beings from the ground rules he set for other living organisms. In so doing, he sowed 400 years of confusion and discord with his notion that the mind and the body were separate phenomena, governed by separate rules.) (…)
But living systems are not really clocklike in their assembly, and organisms are not really machines. (…) The number of elements that compose any living system—an ecosystem, an organism, an organ or a cell—is enormous. In living systems, the specific identities of these component parts matter. Unlike chemistry, for instance, in which an electron in a lithium atom is identical to an electron in a gold atom, all proteins in a cell are not equivalent or interchangeable. Each protein is the result of its own evolutionary trajectory. We understand and exploit their similarities, but their differences matter to us just as much. Perhaps most importantly, the relations between the components of living systems are complex, context-dependent and weak. In mechanical machines, the conversation taking place between the parts involves clear and unambiguous interactions. These interactions result in simple causes and effects: They are instructions barked down a simple chain of command.
In living systems, by contrast, virtually every interesting bit of biological machinery is embedded in a very large web of weak interactions. And this network of interactions gives rise to a discussion among the parts that is less like a chain of command and more like a complex court intrigue: ambiguous whispers against a noisy and distracting background. As a result, the same interaction between a regulatory protein and a segment of DNA can lead to different (and sometimes opposite) outcomes depending on which other proteins are present in the vicinity. The firing of a neuron can act to amplify the signal coming from other neurons or act instead to suppress it, based solely on the network in which the neuron is embedded. (…)
We have revealed the elegant workings of neurons in exquisite detail, but the material understanding of consciousness remains elusive. We have sequenced human genomes in their entirety, but the process that leads from a genome to an organism is still poorly understood. We have captured the intricacies of photosynthesis, and yet the consequences of rising carbon-dioxide levels for the future of the rain forests remain frustratingly hazy.
