Costly yet affordable: accounting for excess in Nature

22 Feb 2013

Daniel Milo
School for Advanced Studies in Social Science (EHESS), Paris


There is no such a thing as a free trait. Cell division, photosynthesis, coma, every activity involves expenses. The size of the trait needs energy for its development and maintenance, so quantity should be treated as a trait too. Since resources are limited and competition is harsh, natural selection optimizes processes, structures and quantities; it reduces unnecessary energy expenditure and other costs, and when needed, it evolves trade-offs between 'more' and 'less'. Yet, organisms exhibit instances that seem to us excessive in amount or size. Most instances of "excess" can be explained by the optimization paradigm. But one phenomenon resists this kind of explanation: range. The paradigm predicts that the values of a system will congregate around the optimal point, yet many systems show a very wide range. An optimized process is one that yields the same product for a lesser cost, or a superior product for the same cost; in ranges, the system obtains the same result with an ever growing cost. Thus, a great number of developmental processes have surprisingly large norms of reaction, yielding non-Gaussian distributions. So ranges are a challenge for Neo-Darwinism. I suggest that they are a by-product of the bias of systems to the plus (+), i.e. to the more than needed. And for reason: the margins of systems to the left of the optimal value are much narrower than their margins to the right, because death is lurking on the left side but only waste lays on the right. This principle leads to a quantitative asymmetry: there is much more 'more' in nature than 'less'. Sometimes 'more' becomes hyperbolic. In distributions that are heavily skewed to the right, we have good reason to suspect that at the end of the long tail, the trait's size or amount is superfluous. Everything involves expenses, so some traits and processes are less constrained by considerations of costs, trade-offs, and optimization than others. Wide ranges are ubiquitous in life, from the molecular level to the behavioral one, so it's hard to imagine an excess-less organism. It follows that organisms have a much higher tolerance for unneeded quantities than is usually assumed; they are robust enough to afford a certain (high?) degree of inefficiency. Ranges are the key to the study of excess. Therefore I propose to create a database of biological ranges. They will offer scientists a new angle on the robustness of living systems, from cells to whole organisms.


current theory lunch schedule