American Scientist

To the Editors:

The disappearance of native species as a result of the introduction of invading species is an alarming problem that is occurring all over the world, as Donald A. Levin elegantly reveals in "Hybridization and Extinction" (May–June). Pertinent to this point, conservation biologists have designated the acronym HIPPO for the many forces that destroy biodiversity. The letters stand for: Habitat destruction, Invasive species, Pollution, Population and Overharvesting. A case in point is the battleground state of Hawaii, which Levin slightly touched on. This apparent island paradise is subject to complicated problems. Its native species have warred with many alien species introduced to the island by human occupation over the centuries. Though Hawaii is still rich in life, it has lost much of its unique biodiversity, and about one-fifth of its existing species are alien species.

Given the global rise in hybrid species, the identification of native, pure species is becoming more difficult. Levin introduces this point with the example of the southeastern U. S. red wolf, where genetic evidence suggests that the animal is a hybrid of coyote and a now-extinct species of gray wolf. This example raises the question of what constitutes both the genetic and philosophical definition of a species worth saving. If many currently rare species are hybrids of other species, which may themselves have become extinct, we need to question our conservation policies and whether it's more worthwhile to protect pure species than hybrid ones. If we wish to safeguard specific phenotypes found in the native, pure species, then the red wolf ought to be protected because it harbors traits that are no longer present in other species of surviving animals. In addition, the need to preserve biodiversity stems from the need to protect the equilibrium of the ecosystem. Our present abundant mongrel species are as important to our present ecosystems as purer species and may be easier to save than many purer species that are becoming extinct. If mongrel species represent genetic novelty and are stabilizing components of their ecosystems, are they not worth saving? It appears that the only alternative is to eliminate both pure and mixed species by failed attempts to save the former and by ignoring the plight of the latter.

In addition, it must be recognized that the genomes of all species have evolved over time through mutation and recombination. These genetic changes are the mechanisms that allow nature to introduce new phenotypes into nature. The red wolf is an example. It has traits not seen in other animals, giving it a distinctiveness worth saving. As habitat destruction continues to plague the biosphere and more hybrid plants and animals emerge on the scene, biologists will need to reflect on how to adapt conservation strategies to changing ecosystems.

John Carvalho
Molecular Genetics Program
St. Louis, Missouri