H Levels of Organization of Nature

The biologists Ernst Mayr³⁰ and Nobel Prize winner Niko Tinbergen³¹ dis­cuss explanation and the levels of analysis or levels of organization in biology in similar ways.

At one level, we note that these birds eat insects and that, during the winter in that part of the country, outdoor insects are scarce. Therefore, wrens mi­grate south to where the insects are because they would starve otherwise (the functional level of explanation). And, because migration south in the colder months has solved the food problem for thousands of generations of wrens, the tendency to migrate is encoded in the wren's genes (the phyloge­netic level of explanation). Both functional and genetic levels speak to the ultimate cause of migration, but ultimate causes do not explain everything. We could know all there is to know about its diet and genome and still not understand why a given wren suddenly decides to fly south one autumn day. It turns out that the electrical activity of cells in the wren's nervous system responds to day length, and, as the hours of daylight decrease, the neuronal activity primes the birds to migrate. Even so, the birds don't go until the tem­perature drops sufficiently; when it does, they take to the air. Shorter day length and cool temperature are physiological (intrinsic and extrinsic, re­spectively) proximate causes. Thus, the answer to the question, “Why did the wren migrate?” is complex: the bird was genetically inclined to do so, food was becoming scarce, the days were getting shorter, and, finally, the weather got cold enough to trigger migration.

We should probably start by asking, “what exactly is an explanation?” An in­tuitively straightforward answer is that an explanation is a statement of the (pre­sumed) cause of something's being the way it is. An explanation often answers the question “why?” We are uncertain about something to the extent that we can't explain it adequately. You'll often hear of scientists wanting to know the mechanism of action of a phenomenon. The mechanism of action is often an explanation that is based on a slightly lower level of organization than the one you're directly working on. If you want to know why one muscle in your arm contracts, you'll need to know which nerves activate it and why they are acti­vated. If you want to know about why nerves cause muscles to contract, you'll need to know about the biochemical reactions that let nerves communicate with muscles. Other properties of explanation include its ability to unify aspects of knowledge by showing the interconnectedness of phenomena.³² Sometimes entirely different kinds of explanation are needed for different levels of natural complexity.

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