Just as European seafaring and exploration brought about an awareness of the diversity of life across the earth, construction and mining, which came with the onset of industrialization in Europe, led to an awareness of change in life forms through time. As work like cutting railway lines or quarrying limestone became commonplace, fossils, or preserved remains, of past life forms were brought into the light.
At first, the fossilized remains of elephants and giant saber-toothed tigers in Europe were interpreted according to religious doctrine. For example, the early 19th-century theory of catastrophism, championed by French paleontologist and anatomist Georges Cuvier, invoked natural events like the supposed Great Flood chronicled in Genesis to account for the disappearance of these species in European lands. Another French scientist, Jean-Baptiste Lamarck, was among the first to suggest a mechanism to account for diversity among living creatures that did not rely upon scriptures. His theory of the “inheritance of acquired characteristics” proposed that behavior brought about changes in organisms’ forms. The famed example was that the first giraffe gained its long neck by stretching to reach the leaves on the highest treetop branches and in turn passed this acquired long neck onto its offspring. While Lamarck’s theory has long since been disproved as a mechanism to account for biological change, his proposal seems likely as a change mechanism for cultural inheritance, and he is credited with making the connection between organisms and the environments they inhabit.
During this same time, British geologist Sir Charles Lyell championed uniformitarianism—a theory that accounts for variation in the earth’s surface. According to Lyell, these variations are the result of gradual changes over extremely long periods of time; although the changes are not obvious at the moment, they are caused by the same natural processes, such as erosion, that are immediately observable. Because the time span required for uni-formitarianism is so long, this theory was incompatible with literal interpretations of the Bible, in which the earth is believed to be only about 6,000 years old.
With industrialization, however, Europeans became generally more comfortable with the ideas of change and progress. In hindsight, it seems inevitable that someone would hit upon the scientific concept of evolution. So it was that, by the start of the 19th century, many naturalists
Notochord A rodlike structure of cartilage that, in vertebrates, is replaced by the vertebral column.
Had come to accept the idea that life had evolved, even though they were not clear about how it happened. It remained for Charles Darwin (1809-1882) to formulate a theory that has withstood the test of time.
Grandson of Erasmus Darwin (a physician, scientist, poet, and originator of a theory of evolution himself), Charles Darwin began studying medicine at the University of Edinburgh, Scotland. Finding himself unfit for this profession, he went to Christ’s College, Cambridge University, to study theology. He then left Cambridge to take the position of companion to British Royal Navy Captain Robert FitzRoy on the H. M.S. Beagle, which was about to embark on a scientific expedition to explore various poorly mapped parts of the world. The voyage lasted for almost five years, taking Darwin along the coasts of South America, to the Galapagos Islands, across the Pacific to Australia, and then across the Indian and Atlantic Oceans to South America before returning to England in 1836.
Observing the tremendous diversity of living creatures as well as the astounding fossils of extinct animals, Darwin began to note that species varied according to the environments they inhabited. The observations he made on this voyage, his readings of Lyell’s Principles of Geology (1830), and the arguments he had with the orthodox and dogmatic FitzRoy all contributed to the ideas culminating in Darwin’s most famous book, On the Origin of Species. This book, published in 1859, over twenty years after he returned from his voyage, described a theory of evolution accounting for change within species and for the emergence of new species in purely naturalistic terms.
Darwin added observations from English farm life and intellectual thought to the ideas he began to develop on the Beagle. He paid particular attention to domesticated animals and farmers’ practice of breeding their stock to select for specific traits. Darwin’s theoretical breakthrough derived from an essay by economist Thomas Malthus (1766-1834), which warned of the potential consequences of increased human population, particularly of the poor. Malthus observed that animal populations, unlike human populations, remained stable, due to an overproduction of young followed by a large proportion of animal offspring not surviving to maturity. Darwin wrote in his autobiography, “It at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to work.”16
Today Darwinian natural selection can be defined as the evolutionary process through which factors in the environment exert pressure, favoring some individuals over others to produce the next generation. Darwin combined his observations into the theory of evolution as follows: All species display a range of variation, and all have the ability to expand beyond their means of subsistence. It follows that, in their “struggle for existence,” organisms with variations to help them survive in a particular environment will reproduce with greater success than others. Thus, as generation succeeds generation, nature selects the most advantageous variations and species evolve. So obvious did the idea seem in hindsight that Thomas Henry Huxley, one of the era’s most prominent scientists, remarked, “How extremely stupid of me not to have thought of that.”17
As often happens in the history of science, Darwin was not alone in authoring the theory of natural selection. A Welshman, Alfred Russel Wallace, independently came up with the same idea at the same time while on a voyage to the Malay Archipelago in Southeast Asia to collect specimens for European zoos and museums. According to his autobiography, a theory came to Wallace while he was in a feverish delirium from malaria. He shared excitedly his idea with other scientists in England, including Darwin, whose own theory was yet unpublished. The two scientists jointly presented their findings.
However straightforward the idea of evolution by natural selection may appear, the theory was (and has continued to be) a source of considerable controversy. Darwin avoided the most contentious question of human origins, limiting his commentary in the original work to a single sentence near the end: “much light will be thrown on the origin of man and his history.” The feisty Thomas Henry Huxley, however, took up the subject of human origins explicitly through comparative anatomy of apes and humans and an examination of the fossils in his book, On Man’s Place in Nature, published in 1863.
Two problems plagued Darwin’s theory throughout his career: First, how did variation arise in the first place? Second, what was the mechanism of heredity by which variable traits could be passed from one generation to the next? Ironically, some of the information Darwin needed, the basic laws of heredity, were available by 1866, through the experimental work of Gregor Mendel (1822-1884), a Roman Catholic monk, working in the monastery gardens in Brno, a city in today’s Czech Republic.
Mendel, who was raised on a farm, possessed two particular talents: a flair for mathematics and a passion for gardening. As with all farmers of his time, Mendel had an intuitive
Natural selection The evolutionary process through which factors in the environment exert pressure, favoring some individuals over others to produce the next generation.
3 Darwin, C. (1887). Autobiography. Reprinted in F. Darwin (Ed.). (1902), The life and letters of Charles Darwin. London: John Murray. 17 Quoted in Durant, J. C. (2000, April 23). Everybody into the gene pool. New York Times Book Review, 11.
Understanding of biological inheritance. He went a step farther, though, in that he recognized the need for theoretical explanations, so at age 34, he began careful breeding experiments in the monastery garden, starting with pea plants.
Over eight years, Mendel planted over 30,000 plants— controlling their pollination, observing the results, and figuring out the mathematics behind it all. This allowed him to predict the outcome of hybridization, or breeding that combined distinct varieties of the same species, over successive generations, in terms of basic laws of heredity. Though his findings were published in 1866 in a respected scientific journal, no one seemed to recognize the importance of Mendel’s work during his lifetime.
Interestingly, a copy of this journal was found in Darwin’s own library with the pages still uncut (journals were printed on long continuous sheets of paper and then folded into pages to be cut by the reader), an indication that the journal had never been read. In 1900, cell biology had advanced to the point where appreciation of Mendel’s laws was inevitable, and in that year three European botanists, working independently of one another, rediscovered not only the laws but also Mendel’s original paper. With this recognition, the science of genetics began. Still, it would be another fifty-three years before the molecular mechanisms of heredity and the discrete units of inheritance would be discovered. Today, a comprehensive understanding of heredity, molecular genetics, and population genetics supports evolutionary theory.
World History
