Punctuated equilibrium also gave credence to another concept promoted by Gould, that of a hierarchy of selection. Rather than trying to find some fundamental unit for selection to act upon, which is perhaps too simplistic a model, why not simply admit things aren't that simple? Why not admit that selection can act on genes, individuals, groups, kinships, and indeed even species? Gould, recalling Wallace, included species among the entities selection acted upon.
Ecologists carry the hierarchy out even further. To understand whole ecological systems, ecologists see evolution affecting all of it. For them, whole communities respond to environmental change or to smaller changes within the system. A faster impala leads to a faster cheetah, or a cheetah that eats more wart hogs and wildebeests, or both. The effects of any change are not isolated, but ripple out, touching many communities. And you can't separate a single ripple; you can't even separate the pond from the shore—each particle influences every other.
The principle of hierarchy of selection added to evolution another tier of complexity, far away from the reductionist influence of Dawkins and far away from the framework of the more physical sciences. If selection works at all these levels, and combines with system constraints and chance, then evolution will never be explainable in terms of simple, rigorous laws and principles. Gould, Mayr, and ecol-ogists assert that biology is not given to the same framework as physics and chemistry. As a science, it is too complex for that.
They suggest a better way to study biology may be through narrative. Scientists should not expect to be able to explain biology in terms of laws and formulas. Perhaps the way Darwin presented his ideas, using description and argument, was after all the most appropriate way to approach it.
Ecologists have opted for this solution for practical purposes. Faced with the job of assessing human impact on the natural world, they can't predict a single scenario. If they try, they'll be wrong too often and no one will listen to them. Complexity going in produces complexity coming out; if ecologists build their models accurately, the multitude of modifying elements produce a multitude of possible endpoints. Since their models can come up with so many different scenarios (depending on what the inputs are and what they can make of the relationships between the inputs), they have instead adopted the use of "if this, then that" narratives, or worst case and best case scenarios. Asked to contribute to policy decisions, the advice they can offer is in the form of stories or descriptions. They no longer can allow themselves to be pinned down to predictions. Far better to keep future plans flexible and contingent—as things go awry, they have a plan ready and waiting to deal with possible consequences.
To suggest that science is telling stories—well-grounded and well-formulated stories, at least—is not the laugher it might have been. The ecologists call this post-normal science.
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