The acceptance
of biological evolutionis an essential part of the modern scientific
explanation of the natural world. Most scientists and major religions in
the Western World have long since incorporated it into their understanding of
nature and humanity. However, some churches still maintain that there
was a special and independent creation of every species and
that life forms do not change through time from generation to
generation. These "creationists" often share beliefs about the
Judeo-Christian Bible that were widely held, even by scientists, during the
early 19th century and before.
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James
Ussher |
The traditional Judeo-Christian version of creationism was strongly reinforced by James Ussher, a 17th century archbishop of Armagh Ireland. By counting the generations of the Bible and adding them to modern history, he fixed the date of creation at October 23, 4004 B.C. During Ussher's lifetime, debate focused only on the details of his calculations rather than on the approach. Dr. Charles Lightfoot of Cambridge University in England had the last word. He proclaimed that the time of creation was 9:00 A.M. on October 23, 4004 B.C.
This belief that the Earth and life on it are only about 6000 years old fit neatly with the then prevalent theory of the "Great Chain of Being." This held that God created an infinite and continuous series of life forms, each one grading into the next, from simplest to most complex, and that all organisms, including humans, were created in their present form relatively recently and that they have remained unchanged since then. Given these strongly held beliefs, it is not surprising that 17th and 18th century European biology consisted mainly of the description of plants and animals as they are with virtually no attempt to explain how they got that way.
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| Carolus
Linnaeus 1707-1778 |
The leading biological scientist of the 18th century was the Swedish botanist Karl von Linné (Carolus Linnaeus in Latin). His 180 books are filled with precise descriptions of nature, but he did little analysis or interpretation. This is to be expected since Linnaeus apparently believed that he was just revealing the unchanging order of life created by God. The goal of documenting change in nature would not have made sense to him. Late in his life, however, he was troubled by the fact that plant hybrids could be created by cross pollination. These were varieties that had not existed before. Linnaeus stopped short of concluding that these plants had evolved.
Despite his limiting research bias, Linnaeus was a first class scientist. His most important contribution to science was his logical classification system for all living things. He described plants and animals on the basis of physical appearance and classified them relative to each other according to the degree of their similarities. He used a binomial nomenclature in naming them. That is to say, organisms were given two Latin names--genus and species. Each genus could have many related species. Each genus was also part of larger categories of living things.
| genus | genus | ||
|---|---|---|---|
| species | species | species | species |
The concept of genus and species was actually developed a generation earlier by John Ray, an English naturalist and ordained minister. However, it was Linnaeus who used this system to name us Homo sapiens (literally, "wise men"). This was very controversial at the time since it implied that people were part of nature, along with other animals and plants.
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| Comte de
Buffon 1707-1788 |
Late in the 18th century, a small number of European scientists began to quietly suggest that life forms are not fixed. The French zoologist, George Louis Leclerc, Comte de Buffon , actually said that living things do change through time and that the Earth must be much older than 6000 years. In 1774, in fact, he speculated that the Earth must be at least 75,000 years old. The Count of Buffon was careful to hide his views in a 44 volume natural history book series. By doing this, he avoided broad public criticism.
While the Count of Buffon was a quiet pioneer in asserting that species can change over generations, he rejected the idea that species could evolve into other species.
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Erasmus
Darwin |
Another late 18th century closet-evolutionist was Erasmus Darwin , the grandfather of Charles Darwin. Erasmus was an English country physician, poet, and amateur scientist. He believed that evolution has occurred in living things including humans. He wrote of this in his poems and other relatively obscure publications. However, like the Count of Buffon, he did not know what caused evolution.
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| Lamarck 1744-1829 |
The first evolutionist who confidently and very publicly stated his ideas about the processes leading to biological change was another late 18th and early 19th century French aristocrat, Jean Baptiste, Chevalier of Lamarck . Unfortunately, his theory about these processes was entirely incorrect.
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| Lamarck's
conception of evolution |
Lamarck believed in the inheritance of acquired characteristics. That is, he believed that evolution occurs when an organism uses a body part in such a way that it is altered during its lifetime and this change is then inherited by its offspring. For example, Lamarck thought that giraffes evolved their long necks by each generation stretching further to get leaves in trees and that this change in body shape was then inherited.
It was easy for the French scientist, George Cuvier , and other critics of Lamarck to discredit his idea of inheritance of acquired characteristics. If this "use-disuse" theory were correct, a loss of your hand in an accident would result in your future children being born with only one hand too. This obviously does not happen.
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| George
Cuvier 1769-1832 |
While Lamarck's explanation of evolution was incorrect, it is unfair to label him a bad scientist. In fact, he was at the cutting edge of biological research for his time. He also was largely responsible for making biology a distinct branch of science.
Despite his criticism of Lamarck, George Cuvier did not reject the idea that there had been earlier life forms. In fact, he was the first scientist to document extinctions of ancient animals. However, he rejected the idea that their existence implied that evolution had occurred--he rigidly maintained the "fixity" of species.
Cuvier advocated the theory of catastrophism . This held that there have been violent and sudden natural catastrophes such as great floods and the rapid formation of major mountain chains. Plants and animals living in those parts of the world where such events occurred were often killed off according to Cuvier. Then new life forms moved in from other areas. As a result, the fossil record for a region shows abrupt changes in species.
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| Charles
Lyell 1797-1875 |
A careful examination of geological deposits led the English scientist, Charles Lyell , to conclude that Cuvier's catastrophism theory was wrong. He believed that there primarily have been slower, progressive changes. Lyell documented the fact that the Earth must be very old and that it has been subject to the same sort of natural processes in the past that operate today in shaping the land. These forces include erosion, earthquakes, glacial movements, volcanoes, and even the decomposition of plants and animals.
Lyell provided conclusive evidence for the theory of uniformitarianism , which had been developed originally by the late 18th century Scottish geologist, James Hutton. This held that the natural forces now changing the shape of the Earth's surface have been operating in the past much the same way. In other words, the present is the key to understanding the past.
This revolutionary idea was instrumental in leading Charles Darwin to his understanding of biological evolution in the 1830's. However, it was not until the late 19th century that most educated people in the Western world finally rejected the theory of catastrophism in favor of uniformitarianism.
Today, we know that our planet has been shaped by occasional
catastrophic events, such as bombardment of large meteors, in addition to the
comparatively slower natural processes suggested by uniformitarianism.
All of these events have potentially affected the rate and direction of
biological evolution.