Early Theories of Evolution
Pre-Darwinian Theories
The acceptance
of biological evolution is 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.
The traditional Judeo-Christian version of creationism was strongly reinforced by James Ussher , a 17th century Anglican archbishop of Armagh in Northern 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 to be that way.
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Carolus Linnaeus |
The leading biological scientist of the mid 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.
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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 which he proposed in his
book Systema Naturae, first published in 1735. In this and
subsequent works, he described plants and animals on the basis of physical
appearance and method of reproduction. He classified them relative to
each other according to the degree of their similarities. He used a
binomial nomenclature |
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John Ray |
The concept of genus and species was actually developed in the late 1600's 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"). He also placed us in the order Primates (a larger, more inclusive category than our genus) along with all of the apes, monkeys, and prosimians. This was very controversial at the time since it implied that people were part of nature, along with other animals and plants. In addition, it meant that we were biologically closer to the other primates than to all other animals.
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Comte de Buffon |
Late in the 18th century, a small number of European scientists began to quietly suggest that life forms are not fixed. The wealthy French mathematician and naturalist, George Louis Leclerc, Comte de Buffon , actually said that living things do change through time. He speculated that this was somehow a result of influences from the environment or even chance. He believed 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. He also suggested that humans and apes are related. Buffon was careful to hide his radical views in a limited edition 44 volume natural history book series called Histoire Naturelle (1749-1804). By doing this, he avoided broad public criticism.
Buffon was an early advocate of the Linnaean classification system. He was also a quiet pioneer in asserting that species can change over generations. However, he publicly rejected the idea that species could evolve into other species. One of his most significant contributions to the biological sciences was his insistence that natural phenomena must be explained by natural laws rather than theological doctrine.
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Erasmus Darwin |
Another late 18th century closet-evolutionist was Erasmus Darwin , the grandfather of the well known 19th century naturalist, Charles Darwin. Erasmus was an English country physician, poet, and amateur scientist. He believed that evolution has occurred in living things, including humans, but he only had rather fuzzy ideas about what might be responsible for this change. He wrote of his ideas about evolution in poems and a relatively obscure two volume scientific publication entitled Zoonomia; or, the Laws of Organic Life (1794-1796). In this latter work, he also suggested that the earth and life on it must have been evolving for "millions of ages before the commencement of the history of mankind."
The first evolutionist who confidently and very publicly stated his ideas about the processes leading to biological change was a French protégé of the Comte de Buffon. He was Jean-Baptiste Chevalier de Lamarck . Unfortunately, his theory about these processes was incorrect.
Lamarck believed that microscopic organisms appear spontaneously from inanimate materials and then transmute, or evolve, gradually and progressively into more complex forms through a constant striving for perfection. The ultimate product of this goal-oriented evolution was thought by Lamarck to be humans. He believed that evolution was mostly due to the inheritance of acquired characteristics as creatures adapted to their environments. 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. Likewise, he believed that wading birds, such as herons and egrets, evolved their long legs by stretching them to remain dry. Lamarck also believed that creatures could develop new organs or change the structure and function of old ones as a result of their use or disuse.
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Lamarck's incorrect idea |
Jean-Baptiste Lamarck |
Lamarck did not invent the idea of inheritance of acquired characteristics but stated it clearly and publicly in an 1809 publication entitled Philosophie Zoologique. It was relatively easy for the French scientist, George Cuvier , and other critics of Lamarck to discredit his theory. If it was correct, the children of cowboys who have developed bowed legs as a result of a lifetime of riding horses would be born with bowed legs as well. That, of course, does not occur. Likewise, the children of professional weight lifters are not born with enlarged muscles.
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George Cuvier |
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 and George Cuvier were largely responsible for making biology a distinct branch of science.
Despite his criticism of Lamarck, 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 and was an internationally respected expert on dinosaurs. However, he rejected the idea that their existence implied that evolution had occurred--he dogmatically maintained the "fixity" of species.
Cuvier advocated the theory of catastrophism , as did most other leading scientists of his day. 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. Cuvier's explanation relied solely on scientific evidence rather than biblical interpretation.
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Charles Lyell |
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A careful examination of European geological deposits in the early 19th century led the English lawyer and geologist, Charles Lyell , to conclude that Cuvier's catastrophism theory was wrong. He believed that there primarily have been slower, progressive changes. In his three volume Principles of Geology (1830-1833), 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.
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James Hutton |
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.