Darwin's Error

IN A letter to Joseph Hooker on January 11, 1844, Charles Darwin wrote: "I was so struck with the distribution of the Galapagos organisms . . . that I determined to collect blindly every sort of fact, which could bear any way on what are species. ... At last gleams of light have come, and I am almost convinced, quite contrary to the opinion I started with, that species are not (it is like confessing a murder) immutable."

What were some of the observations that led Darwin to come to such a conclusion? He had been chosen to be the naturalist aboard The Beagle, commanded by Captain Fitzroy, when it left England to create more accurate navigation charts for sailing round the world by way of Cape Horn. They visited the Galapagos Islands in 1835, where Darwin became fascinated by the variation seen in species.

His observations led him to write: "The natural history of these islands is eminently curious and well deserves attention. Most of the organic productions are aboriginal creations, found no where else; there is even a difference between the inhabitants of different islands; yet all show a marked relationship with those of America, though separated from that continent by an open space of ocean between five and six hundred miles in width."

Darwin's Discovery

Darwin's attention had been drawn by the local governor to the fact that each island had its own peculiar tortoise population, but the significance of that did not occur to him until he began comparing specimens of the mockingbirds in his collection. His diary reads: "My attention was first thoroughly aroused, by comparing together the numerous specimens, shot by myself and several other parties on board, of the mocking thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifaciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham islands belonged to M. melanotes."

He quickly turned to the finches in his collection and found that those from the various islands had all been mixed and labeled as from Galapagos Islands in general. He relied on other collections and identifications provided him by John Gould, a noted ornithologist of his day, when he suspected that some of the finch species were confined to separate islands. Thirteen species of finches! were noted on the basis of differences in size and bill form. He described the birds as a singular group of finches that feed together in flocks on the dry ground, and he emphasized as a curious fact the perfect gradation in the size of the beaks in the different species. The fine line of distincttion between species led him to suspect that some of the finches may be only well-marked races.

One thing was certain to hint, and this was the observation that the Galapagos organisms both plant and animal had their origin in ancestors from the mainland of America. Concepts of change In natural populations were not new to him. His own grandfather, Erasmus Darwin, had expressed ideas along this line of thinking, but Charles, having been trained first as a physician and then as a theologian, had been taught that the Scriptures indicated the fixity of species and thus his reason for writing that to suggest species could change was like confessing a murder.

Darwin and Species

At his home in England, Darwin set about learning all he could about variation in species, and one of his hobbies became raising the various breeds of pigeons. He traced all the variations to the common rock dove of Europe and then suggested that under the control of natural selection, variations in wild populations produced new species in nature. His observation led him to attempt to define the category of species. He wrote:

"In determining whether a form should be ranked as a species or a variety, the opinion of naturalists having sound judgment and wide experience seems to be the only guide to follow."

With such a definition, then obviously species can change. Modem definitions by authorities in taxonomy are no more explicit than Darwin's. Ernst Mayr, a well-known authority of the present, says, "Species has more objectivity than other categories, but it is difficult to define. There are many definitions as there are competent systematists." Mayr, however, suggests that the chief factor in defining a species should be reproductive isolation. On the Galapagos, finches have been subjectively divided not only into thirteen species but also into three genera. These genera distinguish six species of ground finches, six species of tree finches, and a single species of a warbler-like finch.

We can readily agree with Charles Darwin today that the finches, mockingbirds, plants, and other animals of the Galapagos must have originated each from common ancestors on the mainland. The Galapagos Islands are volcanic in origin, having arisen comparatively recently from the ocean's floor, and obviously each species was not especially created for each island. In Darwin's day most special creationists believed that the species were created as they are found. Now we can fully appreciate Darwin's problem and agree with him that island populations originate by the accidental or chance arrival of ancestral types from the continents.

Some scientists suggest natural selection to be the force that creates variation within new expanding populations. Another view is that the Galapagos finches are varied because of the accumulation of genetic differences primarily as a result of isolation. When the initial population was finally established, in the absence of competition some members of the population spread out to exploit every available food source, creating small, partially isolated subpopulations of individuals. These, through genetic inbreeding, be came slightly different from the other subpopulations. We refer to this as genetic drift. Natural selection tends to operate in nature to maintain a population in a steady state of favorably adapted individuals. Large populations remain fairly uniform because unusual variation is quickly diluted by gene flow within the large population.

Variation within the basic type of plant or animal seems to be a rule of nature, but we do not see in all the biological or paleontological world any incontrovertible evidence for change from one basic type to another. On the Galapagos, finches are finches, mockingbirds are mockingbirds, and tortoises are tortoises, and all are readily identified with finches, mockingbirds, and tortoises found on the continents.

Darwin's Mistake

Then where did Darwin go wrong? He failed to recognize that the Biblical account of Creation does not discuss whether changes could or could not take place subsequent to the initial creation of a variety of complex forms of life. It does teach that changes did take place after man sinned. If Darwin had rightly understood the Scriptural account he would not have needed to have a guilt complex. He was perfectly correct in stating that in nature, species are subject to change and that the Galapagos finches had descended from a common ancestor of the finch type, but he carried his generalization into an area of unwarranted speculation when he suggested that inasmuch as the Galapagos species had come from a common stock from the main land it was possible that all living things are related through a common ancestor.

In suggesting such a possibility Darwin committed a sin frequently committed in the biological sciences today, that of overgeneralization. Nature shows only, as our example indicates, that an ancestral finch population gave rise to several species of slightly differing finches. Since the concept of a species has some subjectivity we may also suggest that some of the variation we see in 320 species of hummingbirds, 200 species of tanagers, or 300 species of thrushes may be the result of the type of change that we see in Darwin's finches.

My personal opinion is that at least the six species of the Galapagos ground finches and the six species of tree finches should be classified as races of a single species, creating what some taxonomists call a single polytypic species. However, this premise would depend on how one defines a species. It is interesting to note that major steps to this view point have already been made within bird classification. In 1900 about 19,000 species of birds were described for the world. Our present classification indicates only about 8,620 valid species and 27,000 races, or subspecies.

Darwin's overgeneralization, that all living things may be related through a common ancestor, was the suggestion that enabled men to assume no need for a Creator. The evidence Darwin hoped for to support his speculation—transitional fossil forms and missing links—has not been discovered. It never will be, for in the realm of biology there is ample evidence of the Great Designer.