Evolutionary Biology/Darwin's Life and Impact
Charles Darwin (1809-1882) was one of the most influential individuals in the history of science. Although he published a number of important works during his lifetime, he is best known for The Origin of Species (1859). Although the idea that species evolve was not a new one (see Evolution before Darwin), it was not widely accepted in Darwin's time. Aside from the enormous body of evidence that species in fact do change over time, in Origin, Darwin fully developed natural selection as the first plausible mechanism regarding how they change. A great deal of Darwin's success arose from the details of his life, travels, and the circle of influential individuals with whom he associated.
Robert Darwin (1766-1848) sent his son Charles to medical school at Edinburgh University when he was only 16 years old. Charles found it boring, and withdrew at age 18, after which his father sent him to Christ College in Cambridge to study for the clergy. While at Christ College, Darwin became interested in botany and insects, and he attended several botany lectures. One of Darwin's teachers, John Stevens Henslow, launched Darwin's interest in geology. Professor Henslow was known to teach his students to make careful observations of natural phenomena. While enrolled at Christ College, Darwin found himself unfit for a life as a minister.
The most important experience of Darwin's life was his trip aboard HMS Beagle as a naturalist, a person familiar with natural history, particularly in zoology and botany. Darwin was not the top choice as a naturalist aboard the Beagle; he was very fortunate to even receive this opportunity. Robert FitzRoy, the captain of the Beagle, initially asked Henslow, Darwin's professor, to be the naturalist of the ship, but Henslow's wife discouraged him. Then, Henslow's brother-in-law was approached to replace Henslow, but he too rejected the job. Finally, Henslow recommended Darwin as a well-qualified replacement. Captain FitzRoy was originally cold to the idea of having Darwin on the voyage, but he ultimately decided that he would allow Darwin on the journey. Darwin's position at first was the captains travel companion, since FitzRoy had already given a surgeon named McKormick the naturalist position. McKormick, though, left the position soon after the Beagle departed England, leaving Darwin as the naturalist.
The Beagle left England in 1831, and it returned in 1836. The overall purpose of the voyage was to map uncharted areas of the South American coastline. While aboard the Beagle, Darwin read Charles Lyells Principles of Geology (1830). Lyell was a famous geologist and eventually became a lifelong friend of Darwin. He developed the theory of uniformitarianism, which holds that the Earth is very old, and that geological changes are due to slow, continuous processes. These processes, such as erosion and deposition, are constant. Lyell's uniformitarianism view opposed the generally-accepted catastrophism view proposed by Georges Cuvier. Catastrophism is the theory that changes in the earth are due to natural disasters.
Later Life and Sickness
A month after returning to England, Darwin proposed to Emma Wedgwood, his first cousin. On January 30, 1839, they got married. Darwin became sick around this time. He may have been infected by Trypanosoma cruzi, a parasite prevalent in both Central and South America. The infection causes Chagas' disease. Darwin showed many of the symptoms related to Chagas disease: flatulence, vomiting, palpitations, and insomnia. Whatever sickness Darwin had, it caused him to stay near home for much of the rest of his life. Darwin was not even able to attend his father's funeral due to the severity of his illness. However, this sickness may have given him more time to read, think, and write. He inherited a lot of money, and his wife brought a significant amount of money into the marriage, affording him additional time towards his studies.
Basis of Evolution
From recovered notes, historians know that Darwin saw unique species of plants and animals in South America, such as finches and iguanas. He noticed that organisms differed more as a function of geographic distribution than as a function of climate: the temperate South American animals more closely resembled the tropical South American animals than the temperate European animals. Also, some characteristics of the fossils Darwin observed in South America paralleled some contemporary South American organismal features. While on the Galápagos Islands, Darwin had collected many species of finches.
After returning to England, Darwin gave this collection of finches to John Gould, a man who studied birds. Gould measured the differences in beak sizes of the finches, and his measurements showed great variances. The sample included small, medium, and large beaks. Darwin began to ponder how and why this diversity in the finches' beak structure took place. He imagined that these changes within populations may better adapt them to their local environment. He soon realized that adaptation and speciation were closely related. A new species may develop as a result of slow, gradual adaptations, just as a big change in the Earth could occur from slow continuous processes. Darwin thus began to formulate his theory of natural selection as the main process in evolution.
Almost a half century earlier, Robert Malthus had written An Essay on the Principles of Population (1798). This essay explained that human growth rate is geometric whereas food production is only arithmetic. Continuation of geometric human growth in this fashion leaves a huge discrepancy between food and population. Darwin read this in 1838, and he pictured this discrepancy as a struggle for existence. In most cases, the struggle for existence is not an obvious battle, and some may not even regard it as a struggle. What actually takes place is an inheritance of favorable characteristics. "Favorable characteristics" cause individuals to survive better. Since they survive better, individuals that inherit favorable characteristics will gradually represent greater numbers in the population. Darwin saw that eventually favorable characteristics would replace the unfavorable ones, and a new species would arise.
Natural Theory and God
Before Darwin's publications, natural theology dominated. Natural theology is the idea that God's plan can be known through human reason. According to this logic, adaptation of any given organism is evidence that God intended the adaptation for a specific function. Knowing that his theory would contradict the beliefs of natural theology and would cause anger once published, Darwin procrastinated publication.
Besides coming from religious individuals, strong beliefs came from scientific minds. Those who did believe in evolution around Darwin's time thought that it occurred by the inheritance of acquired characteristics, a theory known as Lamarckism (proposed by Jean-Baptiste Lamarck). Lamarckism claims that the parts of the body that are used frequently during an individuals lifetime are exaggerated in the offspring. This, however, was later proven false through genetics. The theory of "Inheritance of Acquired Characters" as it is called by scientific community was proved false by August Weismann, a German evolutionary theorist. Weismann cut the tails of lab rats over many generations but could not find any change in the length of the tails of new-born rats. He also concluded that piercing of ear pinna, wearing of tight clothes for a slimmer waist by women of middle ages, all carried out over generations doesn't change any of those characters during birth. The changes an individual makes to his body in his lifetime do not alter his sex cells. Only changes that affect the "Germ Cells" or sex cells of an individual in lifetime are inherited by the next generation.
Origin of Species and Publication
Throughout his life, Darwin corresponded with scholarly groups, friends, and colleagues. Lyell knew of Darwin's ideas regarding natural selection, and suggested he publish them quickly. Not long after, Darwin received a letter from Alfred Russell Wallace, another British naturalist working in Southeast Asia. Wallace wanted Darwin to review his work before publication. As Darwin began to read, he was shocked to find that Wallace's theory was almost exactly the same as his own. Initially, Darwin worked with Wallace, and in 1858, they publicly announced to the Linnaean Society of London the theory of natural selection. Because Darwin had begun writing notes on his theory of natural selection on September 28, 1838, well before Wallace, and he had much more thoroughly explained it, he is credited for the theory of natural selection.
In 1859, the first edition of The Origin of Species was published under the name: On The Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. His theory of natural selection states that the individuals best adapted to their environment will produce the most offspring. This will result in an increase in the proportion of individuals with the favorable genotypes. Although this increase in favorable genotypes is the cause for natural selection, genetics was not well-understood until Gregor Mendel's paper, written in 1865, was re-discovered in 1900.
In The Origin of Species, Darwin did not relate his theory of natural selection to humans because he knew it would cause even more outrage among his friends and family. In addition to The Origin of Species, Darwin wrote 19 other books, and he addressed human evolution in two of his publications late in his life: The Descent Of Man, And Selection In Relation To Sex (1871) and Expression Of Emotions In Man And Animals (1872).
Darwin's observations, experiments, and theories affect many scientific fields, including ecology and geology. Even modern day pesticide companies take Darwin's theory of natural selection into account when developing a mixture of chemicals targeted for a certain pest. Knowing that natural selection will favor a pest with resistant genes and cause this chemically resistant pest to grow in proportion, developers periodically change the chemical composition.
Darwin revolutionized the world of science with his publication of The Origin. His theory came to affect the entire culture because it was seen to question the very underpinnings of the worldview. The debate continues even today as is seen with the creationism versus evolution controversy in some school systems. Darwin's theory of natural selection unified biology, and he unalterably changed the world. The "Theory of Evolution" had profound effect on all other branches of science as well. It was for the first time during the course of scientific history, that science was separated from the concept of god/religion and was purely judged on the merits of experiment, observation and inference. In a way Darwin's theory provided complete freedom to science.
Campbell, Reece. Biology, Sixth edition. Benjamin Cummings. 2001.