Room of One's Own

Natural History, Nov, 1997 by Stephen Jay Gould

We can at least pose such a question without logical contradiction, and we can test certain ideas about minimal discrepancies in body size, feeding preferences, and so on. Much useful research has been done on this subject, but no general answers have emerged. And none may be possible (at least in such simplistic form as "no more similar than a 10 percent difference in body weight on average"), given the irreducible uniqueness of each species and each group of organisms. Beetle rules (if such there be) will almost surely not work as fish rules, not to mention the vastly more different world of bacteria rules.

But if we cannot generate quantitative laws of nature about numbers of species in a single place, we can at least state some general principles. And the rule behind Jerusalem's Status Quo, whatever its moral dubiety in the ethical systems of Homo sapiens, provides a good beginning: large numbers of species can be crammed into a common territory only if each can commandeer some room of its own and not always stand in relentless competition with a maximally similar form.

Two general strategies may be cited, the second far more interesting than the first, for acquiring the requisite "breathing room"--a little bit of unique space that no other species contests in exactly the same way. In the first strategy--the "Holy Sepulchre solution" if you will--two species perceive the surrounding environment in basically the same manner and therefore must divide the territory to keep out of each other's way. Division may be strictly spatial, as in my fraternal dispute about our single common room. But organisms may also use nature's other prime dimension and construct temporal separations as well. The Status Quo divides the space within the Church of the Holy Sepulchre, but the agreement also decrees when the unitary domain of sound belongs to the masses, instruments, and voices of various competing groups.

To make an ugly analogy, based on cruel social practices now thankfully abandoned, but in force not long ago, I encountered both spatial and temporal modes of segregation when I began my college studies in southwestern Ohio during the late 1950s. The town movie theater placed whites in the orchestra and blacks in the balcony, while the local skating rinks and bowling alleys maintained different "white" and "Negro" nights. (Student and community activism, spurred by the nascent Civil Rights movement, fought and vanquished these cruelties during my watch. I remember my own wholehearted and, in retrospect, pretty inconsequential participation with great pride.)

An instructive evolutionary example of this first strategy can be found in a classical argument about modes of speciation, or the origin of a new species by branching from an ancestral population. Such branching can only occur if a group of organisms can become isolated from the parental population and begin to breed only among themselves in a different environment that might favor the evolution of new features by natural selection. (If members of the separating group continue to interact and breed with individuals of the parental population, then favorable new features will be lost by dilution and diffusion, and the two groups will probably reamalgamate, thus precluding the origin of a new species by branching.)