Sunday, February 24, 2013

Evolution Before Darwin

Evolution Before Darwin

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. Aristotle suggests a transition between the living and the nonliving, and theorizes that in all things there is a constant desire to move from the lower to the higher, finally becoming the divine

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.

Immanuel Kant

The German philosopher Immanuel Kant (1724-1804) 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

Carolus Linnaeus, or Carl Linné (1707-1778), 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.

Erasmus Darwin

Charles Darwin's grandfather Erasmus Darwin (1731-1802) 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

Jean-Baptiste Lamarck's (1744-1829) 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.

Thomas Malthus

Thomas Malthus' (1766-1834) 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.

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.