First Published March 2, 2016, written by Denis Lynn
There is a popular belief in “the Balance of Nature.” This has likely been our belief for thousands of years. It arises possibly from the observation that the world around us is generally the same from year-to-year, decade-to-decade, and even generation-to-generation. The trees grow but do not change dramatically in numbers; the numbers of other plants and of animals generally do not dramatically change. That is, things tend to “stay the same” or there appears to be a “Balance of Nature”. In fact, it is the exceptions that prove the rule: plagues of locusts, floods, and droughts.
How to explain these exceptions? If we take the explanations in the Greek writings about the workings of nature as indications, it was likely that our ancestors explained these exceptions as the workings of the mysterious forces of the Universe – eventually conceived of as gods. Egerton describes this as “providential ecology.” Providential ecology was still the primary view as the JudeoChristian worldview flourished. If the exceptions brought hardship on us, then we looked to our actions as having displeased the gods – sacrifices and prayers were needed to “re-balance” the ecology.
Throughout history, and certainly by the 1600s and 1700s, there were attempts at understanding the wisdom of the gods by providing naturalistic explanations for the characteristics of species. For example, the Greeks observed how wise it was that prey, such as rabbits, were much more fecund than their predators, like foxes, and so a “balance” was preserved between predator and prey. Carolus Linneaus, the Swedish father of taxonomy and perhaps also of ecology, suggested that intimate and specific relationships between species, created by God, “contribute and lend a helping hand towards preserving every species, and … that the death and destruction of one thing should always be subservient to the restitution of another” (p. 336, Egerton, 1973). One might say “a place for every thing, and every thing in its place.”
However, the notion that a fixed number of species had been created and that these all had a significant role in Creation was challenged by the discovery of fossils: the remains of once living organisms that seemed to be very different from anything alive. Furthermore, some fossil aquatic organisms were discovered near the tops of mountains – so not every thing was in its place, neither in terms of its interactive role in the ecosystem nor in relation to its habitat – what once was apparently underwater is now on top of the world! Scientists could not believe that species were extinct, and John Ray, an Anglican clergyman naturalist, argued in the late 1600s that once Europeans had explored the whole globe, living “fossil” forms would be found. A century later, with much of the world explored, this position was untenable. Certainly by the time Darwin’s travels ended, there was little doubt that many species had become extinct, challenging the notions of “balance” and Special Creation. Jean-Baptiste Lamarck, a French biologist in the 1800s, resolved the problem of extinctions by arguing that species changed through time, originating every moment from the mud, and progressing through a series of transformations from unicells to multicells. This, of course, clearly challenged the notion of a Special Creation, which caused Lamarck problems with his more religious colleagues, but it resolved the problem of fossils: fossils were just older stages of existing species.
What might have caused these extinctions? Up to the 1800s, competition between individuals and between species was considered antithetical to the notions of “harmony” and “balance” in Nature. Charles Lyell, the great geologist of the 1800s, however firmly emphasized competition as a cause of extinctions. Darwin had read Linnaeus, Lyell, and on discovering Malthus, formulated his theory of natural selection premised on the existence of competition between members of a species in their struggle for existence. Yet, Darwin it seems implicitly still believed in some kind of balance as the inspirational last paragaph of “The Origin of Species” suggests: “It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us.”
In contrast, Alfred Russel Wallace, the instigation for Darwin to publish “The Origin”, wrote in his 1855 notebook: “Some species exclude all others in particular tracts. Where is the balance? When the locust devastates vast regions and causes the death of animals and man, what is the meaning of saying the balance is preserved?” (p. 339, Egerton, 1973). Wallace’s musings anticipated the views of most contemporary ecologists who consider “the Balance of Nature” an untestable hypothesis. Simberloff (2014) concludes “It is increasingly difficult to imagine what sorts of empirical or observational data could test the notion of a balance.” Yet, if one carefully defines what one means, “balance” can be observed in Nature.
Further Reading: Egerton. 1973. Quart. Rev. Biol. 48:322; Simberloff. 2014. PLOS Biology DOI: 10:1371/journal.pbio.1001093
– Denis Lynn, Professor Emeritus, Integrative Biology, University of Guelph