Life Science: Session 5
Darwin and Natural Selection
Who was Charles Darwin?
The diversity of the living world has long inspired naturalists and scientists to speculate on its origin. Up until the 19th century, the most popular explanation for the diversity of life on Earth was a supernatural force or god(s). It wasn’t until Charles Darwin’s work in the mid-1800s that the scientific and lay communities began to seriously consider the possibility that life evolved from ancestral forms by strictly natural processes.
As a naturalist aboard the H.M.S. Beagle, Darwin made observations – particularly in the Galapagos Islands —that would later be the foundation for his theory of evolution. What distinguished his theory from others at the time — such as Jean-Baptiste Lamarck’s theory of evolution by the inheritance of acquired traits — was his proposal of natural selection as the mechanism.
What are the principles underlying the theory of evolution?
Darwin was acquainted with principles set forth by the economist Thomas Malthus, who wrote of overpopulation in the context of human civilization. Malthus observed that humans produce more offspring than their food supply can support, which makes competition for limited resources inevitable. Darwin saw connections to the natural world, where habitats are often populated by organisms that have a much greater capacity to reproduce than the environment has the capacity to support. Darwin was also knowledgeable about the practice of artificial selection, where humans essentially direct evolution by manipulating heredity.
Applying these ideas to the natural world, Darwin envisioned a “struggle for survival” where those that survived were somehow more “fit” — that is, better suited for that particular environment. Darwin proposed that “survival of the fittest” resulted in differential reproduction, where those individuals in a population that possessed beneficial traits would produce more offspring. This was natural selection, where nature "selects" which variants in a population survive and reproduce. Darwin proposed that, over time, natural selection results in evolution.
In 1859, Darwin published his life’s work, “The Origin of Species.” The theory of evolution by natural selection rocked the scientific community as well as the public. Interestingly, another scientist, Alfred Russell Wallace, had conceptualized evolution by natural selection. Darwin, however, generally receives the credit.
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