Contrary to many assumptions, evolutionary theory did not begin in 1859 with Charles Darwin and The Origin of Species. Rather, evolution-like ideas had existed since the times of the Greeks, and had been in and out of favor in the periods between ancient Greece and Victorian England. Indeed, by Darwin's time the idea of evolution - called "descent with modification" - was not especially controversial, and several other evolutionary theories had already been proposed. Darwin may stand at the beginning of a modern tradition, but he is also the final culmination of an ancient speculation.

Evolution in Greece

While the Greeks did not specifically refer to their concepts as "evolution", they did have a philosophical notion of descent with modification. Several different Greek philosophers subscribed to a concept of origination, arguing that all things originated from water or air. Another common concept was the idea that all things descended from one central, guiding principle.

  • Thales ( 624 - 546 BCE): asserted that all things originated from water.

  • Anaximander (610 - 546 BCE): With his assertion that physical forces, rather than supernatural means, create order in the universe, Anaximander can be considered the first scientist. He is known to have conducted the earliest recorded scientific experiment. He suggested that living beings gradually developed from moisture with warmth. He also thought that the first humans were born, fully formed, from the wombs of fish, since they needed care for a long time.

  • Anaximenes (585 - 528 BCE): Thought air was the principle of all things, and regarded the process as a thinning or thickening.

  • Empedocles (490 - 430 BCE): Thought that the first creatures were not fully formed but consisted of unconnected limbs. He established the concept of everything in the universe being made up of four elements: fire, air, water and earth, which was the standard for the next two thousand years.

  • Aristotle (384  – 322 BCE): The Great Chain of Being: He thought there was a transition between the living and the nonliving, and theorized that in all things there is a constant desire to move from the lower to the higher, finally becoming the divine.

  • Lucretius (99 - 55 BCE): He was the first to suggest extinctions and that the survivors survived by "cunning or speed".

Medieval Theories

During medieval times, the idea of evolution was quite out of fashion, since the time was dominated by the christian theory of special creation. This idea, which argued that all living things came into existence in unchanging forms due to divine will, was notably in opposition to the concept of evolution.

Medieval thinking was also, oddly enough, confused by the idea of spontaneous generation, which stated that living things can appear fully formed from inorganic matter. In this view, maggots came from rotting meat, frogs came from slime, etc. This sort of a concept prevented both genetic thinking and speculation about evolution or descent with modification. Nevertheless, a few philosophers theorized about some sort of teleological principle by which species might derive from a divine form.

James Ussher - 1581-1656

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.

Immanuel Kant - 1724-1804

The German philosopher Immanuel Kant developed a concept of descent that is relatively close to modern thinking; he did in a way anticipate Darwinian thinking. Based on similarities between organisms, Kant speculated that they may have come from a single ancestral source. In a thoroughly modern speculation, he mused that "an orang-outang or a chimpanzee may develop the organs which serve for walking, grasping objects, and speaking-in short, that lie may evolve the structure of man, with an organ for the use of reason, which shall gradually develop itself by social culture".

Biological Conceptions of Evolution

The preceding discussion has focused on the philosophical components of evolutionary theory, but precursors exist for its biological aspects as well. Indeed, as mentioned above, by Darwin's time the concept of descent with modification was hardly controversial - it was only the mechanism, the rate of modification, and the ultimate origin of life that were being debated. Darwin's major breakthrough consisted in providing a plausible mechanism to drive change in organisms.

Carolus Linnaeus - 1707-1778

Carolus Linnaeus, or Carl Linné, is considered the father of modern taxonomy for his work in hierarchical classification of various organisms. At first, he believed in the fixed nature of species, but he was later swayed by hybridization experiments in plants, which could produce new species. However, he maintained his belief in special creation in the Garden of Eden, consistent with the Christian doctrine to which he was quite devoted. He still saw the new species created by plant hybridization to have been part of God's plan, and never considered the idea of open-ended, undirected evolution not mediated by the divine.

The concept of genus and species was actually developed in the late 1600's by John Ray, 1627-1705, 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.

Late in the 18th century, a small number of European scientists began to quietly suggest that life forms are not fixed.  The French mathematician and naturalist, George Louis Leclerc, Comte de Buffon, 1707-1788, 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.

Erasmus Darwin - 1731-1802

Charles Darwin's grandfather Erasmus Darwin  was also a distinguished naturalist with his own intriguing ideas about evolution. While he never thought of natural selection, he did argue that all life could a have a single common ancestor, though he struggled with the concepts of a mechanism for this descent. He also discussed the effects of competition and sexual selection on possible changes in species. Like Lamarck, Erasmus Darwin subscribed to a theory stating that the use or disuse of parts could in itself make them grow or shrink, and that unconscious striving by the organism was responsible for adaptation.

Jean-Baptiste Lamarck - 1744-1829

Jean-Baptiste Lamarck's  theory of evolution was a good try for his time, but has now been discredited by experimental evidence and the much more plausible mechanism of modification proposed by Darwin. Lamarck saw species as not being fixed and immutable, but rather in a constantly changing state. He presented a multitude of different theories that he believed combined to explain descent with modification of these changing species.

Lamarck subscribed to a number of what we now know to be false beliefs about inheritance. First, like Erasmus Darwin, he argued for strong effects of the use and disuse of parts, which he thought would make the relevant parts change size or shape in accordance with their use. Second, Lamarck believed that all organisms fundamentally wanted to adapt themselves to their environment, and so they strove to become better adapted. The belief most commonly associated with Lamarck today is his idea of the inheritance of acquired characteristics. This theory stated that an organism could pass on to its offspring any characteristics it had acquired in its lifetime. For example, if a man exercised and thus developed strong muscles, his offspring would then have strong muscles at birth.

George Cuvier - 1769-1832

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.

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.

A careful examination of European geological deposits in the early 19th century led the English lawyer and geologist, Charles Lyell, 1797-1875, 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.

Lyell provided conclusive evidence for the theory of uniformitarianism, which had been developed originally by the late 18th century Scottish geologist, James Hutton - 1726-1797.  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.

Thomas Malthus - 1766-1834

Thomas Malthus' theory of population growth was in the end what inspired Darwin to develop the theory of natural selection. According to Malthus, populations produce many more offspring than can possibly survive on the limited resources generally available. According to Malthus, poverty, famine, and disease were natural outcomes that resulted from overpopulation. However, Malthus believed that divine forces were ultimately responsible for such outcomes, which, though natural, were designed by God.

Robert Grant - 1793-1874

He wrote Vestiges of the Natural History of Creation. It argued not only for biological evolution, but chemical and cosmological as well. It was largely scorned and was more of a philosophical work than a scientific one. But it was still very  influential on Darwin and Alfred Russell Wallace.

Charles Darwin and Alfred Russel Wallace

Charles Darwin and Alfred Russel Wallace both independently developed the idea of the mechanism of natural selection after reading Thomas Malthus' Essay on the Principle of Population (1798). However, Darwin had been turning the problem over in his mind for some twenty years before he first published The Origin of Species. Moreover, Darwin was much more willing to explore the implications of natural selection, particularly in relation to humans, than Wallace was. In addition, Wallace was a champion of rather radical social causes and later openly embraced spiritualism - all elements that resulted in the downplay of his role in the discovery of natural selection.

While George Cuvier and Charles Lyell strongly disagreed about how the earth got to be the way it is today, they both rejected the idea of biological evolution.  However, neither man accepted a traditional biblical account of creation and a young earth.  Cuvier did not live long enough to learn about Charles Darwin's proof of evolution, but Lyell did.  He came to accept this proof in the early 1860's along with most leading scientists of that time.  Lyell also became a friend of Charles Darwin.

Darwin's Early Ideas

Darwin proposed a few ideas before he came up with natural selection. One was called the Pangenetic hypothesis. It attempted to explain how acquired characteristics worked. This hypothesis proposed that cells produce small particles called pangenes or gemmules which end up in sex cells. When passed on to the offspring, the pangenes are able to exactly reproduce the organ in which they originated.

Another hypothesis by Darwin was the evolution of monads. This hypothesis stated that species adapt and old species are replaced by new ones, so the overall number of species remains the same. Monads arose by spontaneous generation and would evolve to become an ancestral species.

A modification of the monad hypothesis was that if a monad stopped producing new species it would die out.


Some Books:


No comments:

Post a Comment