Competition is greatest between neighbors

Darwin’s basic theory of evolution, by itself, did not account for the tree-like, hierarchical pattern the species were thought to form. Darwin was keenly aware of this shortcoming and wrestled with it for years. He finally conceived of a solution for why modified offspring would continue to evolve away and diverge from their parents. The principle of divergence, the last major theoretical addition before Darwin published his book, held that competition tends to be strongest between the more closely related organisms. This would cause a splitting and divergence, resulting in the traditional evolutionary tree pattern. (Desmond and Moore 1991, 419-420; Ridley, 378-379)

But no such trend has been observed. In a major study of competition between freshwater green algae species, the level of competition between pairs of species was found to be uncorrelated with the evolutionary distance between the pair of species. As the researchers explained, Darwin “argued that closely related species should compete more strongly and be less likely to coexist. For much of the last century, Darwin’s hypothesis has been taken at face value […] Our results add to a growing body of literature that fails to support Darwin’s original competition-relatedness hypothesis.” (Venail, et. al., 2, 9) The team spent months trying to resolve the problem, but to no avail. As one of the researchers explained:

It was completely unexpected. When we saw the results, we said “this can’t be.” We sat there banging our heads against the wall. Darwin’s hypothesis has been with us for so long, how can it not be right? … When we started coming up with numbers that showed he [Darwin] wasn’t right, we were completely baffled. … We should be able to look at the Tree of Life, and evolution should make it clear who will win in competition and who will lose. But the traits that regulate competition can’t be predicted from the Tree of Life. (Cimons)

Why this long-standing prediction was not confirmed remains unknown. Apparently there are more complicating factors that influence competition in addition to evolutionary relatedness.

References

Cimons, Marlene. 2014. “Old Idea About Ecology Questioned by New Findings.” National Science Foundation.

Desmond, Adrian, James Moore. 1991. Darwin: The Life of a Tormented Evolutionist. New York: W. W. Norton.

Ridley, Mark. 1993. Evolution. Boston: Blackwell Scientific.

Venail , P.A., A. Narwani , K. Fritschie, M. A. Alexandrou, T. H. Oakley, B. J. Cardinale. 2014. “The influence of phylogenetic relatedness on competition and facilitation among freshwater algae in a mesocosm experiment.” Journal of Ecology, DOI: 10.1111/1365-2745.12271.