Evolution: The Highlights

Darwin began his “systematic enquiry” upon his return home in 1836. During his voyage, Darwin began to question the overwhelming diversity of living things. Just as the earth’s landscape was gradually altered through vast expanses of time (he read Lyell’s Principles of Geology while on the trip), was it possible that plants and animals had been changed through time? He sought explanations that would integrate what he had learned on his voyage around the world. Darwin labored away on his “species work” for 22 years. He might have withheld his view on the transmutation of species from the British public even longer had not his hand been forced by Alfred Russel Wallace. In 1858, Wallace sent Darwin an essay of his to review. To Darwin’s shock, it contained the essence of his own “species work. ” Wallace independently arrived at the conclusion that species were mutable and that natural selection was the principal mechanism. Wallace had written his version over the span of three days while suffering from the ill effects of a bout of malaria! Papers by Darwin and Wallace were read before the Linnean Society of London on the 1st of July 1858. A little over one year later, Darwin’s magnum opus appeared in print. It had a resounding Victorian title, On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life, but was an abstract of a large work Darwin had in mind.

The first edition of The Origin of Species… amounted to 1250 copies and was sold out on the first day (24 Nov. 1859). It was a great success not only scientifically, but commercially as well. New printings were called for in rapid succession: 1859 (2nd), 1861, 1866, 1869, and 1872 (6th). Darwin’s Origin actually contains two theories: (1) the theory of evolution; (2) the theory of evolution by natural selection.

The facts that Darwin collected in support of the theory of evolution can be grouped into a small number of categories. These are (1) comparative anatomy, (2) embryology, (3) variability of domestic plants and animals, (4) biogeography, and (5) paleontology. Within the realm of comparative anatomy, Darwin noted the existence of homologous structures (features that are similar in development and construction but have different functions, like the hand of man, a bird’s feathered wing, the front flipper of a whale, and the membranous wing of a bat) and pointed out that these structural similarities suggest common ancestry. He observed that very young embryos of fishes, amphibians, birds, and mammals are strikingly similar (they all possess a dorsal tubular nerve cord, pharyngeal gill slits, and a postanal tail). These embryological similarities (there are others) also suggest common ancestry. A few examples come to mind that demonstrates that evolutionary change can occur within a relatively short time; this is notable in the plants and animals that have come under man’s influence. Darwin remarked at length on breeds of pigeons; his discourse on pouters, tumblers, barbs, carriers, runts, Jacobins, fantails, laughers, trumpeters, and turbits are but vaguely familiar to many of us. To make this point more palatable, I suggest that you take a trip to the nearest fruit and vegetable market. While there, gather the following items in your cart: cabbage, kohlrabi, broccoli, cauliflower, brussels sprouts, and kale. They differ distinctly in appearance, but all are varieties of a plant in the mustard family called Brassica oleracea. The original wild type (which is most similar to kale in appearance) was cultivated in the eastern Mediterranean region for only a few centuries. These variations within a species provide additional evidence for the plasticity of species and support the theory of evolution. The field of biogeography emphasizes historical events of migration and extinction and attempts to elucidate and qualify the factors responsible for both present and past distributions of organisms on the face of the earth. Darwin noted that South American animals, regardless of whether they came from hot or cold regions, were more similar to each other than to other animals from similar climatic regimes elsewhere. The discipline of paleontology delves into the morphology, paleogeographic distribution, and paleoecological and systematic relationships of fossil organisms. Darwin recognized that the fossils from South America resembled living South American forms more closely than any other ones known at the time.