The Humpty-Dumpty Problem
Even when we understand their parts, living things are hard to put back together
A New Harmony
Despite its limitations, reductionism as a research strategy in biology has proven phenomenally successful. The ascendancy of the life sciences, from the discovery of DNA in 1954 to the sequencing of the human genome in 2003, attests to the power of the reductionist approach. We cannot and will not solve the central challenges of biology without understanding in detail how the component parts operate. My argument is not with reductionism itself, but with the idea that it represents the only viable strategy for understanding the living world. And here, too, I want to be careful: Some of the arguments about “irreducible complexity” or “emergence” flirt dangerously with pre- and post-Cartesian animist notions of life forces, ideas that lie beyond the realm of science. Acknowledging the limitations of reductionism does not an anti-materialist make. The living world in all of its contingency and beauty is still the material world and, as such, the result of material forces.
But the days when we could have blind faith in the power of reductionist deconstruction are over. Humpty lies in fragments. Fortunately for us, a new approach is taking shape to replace the seductive appeal of reductionism. We biologists may have bought a little too much of what Descartes had to sell, but as the limits of naive reductionism become more obvious, additional methods emerge for understanding the complexity of life. This new, interactionist perspective on living systems, with its emphasis on the interplay of parts, has benefited from new computational tools and experimental approaches. Whole new subfields in the life sciences, as well as productive interactions among existing disciplines, have emerged. Systems biologists, complexity theorists and newly minted biologists now attend as carefully to the ways in which parts come together as they do to the parts themselves. In the process, features of living systems that we once carelessly overlooked (or destroyed) in our haste to deconstruct now snap into focus. We are, for instance, beginning to understand that modularity and redundancy are inherent features of all levels of biological organization. These features characterize systems that are simultaneously resilient and capable of evolving. They are the calling cards of life.
The current emphasis on interactions also ushers in a new kind of conceptual harmony in biology. The latter half of the 20th century was marked by an apparent and unnecessary gulf between those branches of biology that studied parts—cells and molecules—and those that focused on organisms and ecosystems. The former, committed to reductionism, saw themselves as ascendant, as replacing descriptive natural history with rigorous, experimentally driven hard science. The latter, by contrast, seemed defensive. They were unwilling to concede the potential utility of the reductionist approach or to advocate for the importance of evolutionary history at all levels of biological organization. But now, chastened by experience, we have been reminded that the living world is neither wholly reducible nor fundamentally irreducible. Instead, we have come to understand through biology’s one Theory of Everything, evolution, that the unity and the diversity of the living world are inseparable. Evolution has crafted the very relation between parts and wholes that our science should seek to emulate: Neither is viable without the other. The questions we are asking as biologists are profound and profoundly difficult. Meaningless discussions about what kind of biology is best must give way to a more nuanced dialectic. It is time for a science as subtle as its objects of study.