What is evolution? Evolution is a process of change in our genetic makeup that has occurred over billions of years. Charles Darwin is the most well known figure in evolutionary theory, but many other scientists and philosophers have contributed to the scientific investigation of our origins.
Creationism
Early philosophers considered whether life changed over time. Aristotle, who lived from 384bc to 322bc, believed that living things had a specific unchanging organization. His ideas about life arose from his observation that different groups of organisms such as humans, animals and plants had certain defining characteristics which suited them to their natural environments.
The perfect fit of different organisms to their environments supported Aristotle's previous understanding of creation as described in the old testament of the bible. Theories of creationism dominated the scientific community through the 1700s. The scientist Carolus Linnaeus developed a two part scientific naming system which organized living things according to how they were created, rather than their genetic relationships.
Age of the Earth
Theories of creationism saw the world as fairly young, static and unchanging. In order for the theory of evolution to develop, ideas about the age of the earth had to be investigated. Paleontology, the study of fossil remains, lead scientists to reevaluate the age of earth. When scientists looked at the layers of the earth they saw fossil remains of previously unknown animals that had lived and died out over time. The scientist Georges Curvier believed that extinctions of species had to do with catastrophic events, instead of slow changes over time.
Another scientist, James Hutton, argued that changes in geologic features could be explained by gradual natural forces. Charles Lyell, the leading geologist of the time, proposed that gradual natural forces were constant over time. For slow natural forces to create mountains and other geologic features, they would need to operate for very long periods of time. Hutton and Lyell's ideas lead Darwin to believe that the earth was much older than originally thought.
Early Evolutionary Theory
Not all evolutionary theory was accurate, and much about evolution is still being discovered today. An early evolutionary theorist, Jean Baptiste-de Lamarck, incorrectly proposed a theory of use and disuse. According to Lamarck, physical features that were used most often would be passed down to offspring. Therefore, a giraffe that repeatedly reached out to bite leaves would pass on a longer neck to its offspring. Unfortunately Lamarck's explanation of evolution was incorrect and no scientific evidence has supported his claims. While evolution does occur in an adaptive sense, the mechanism for inheritance lies within our DNA, not within the use of our muscles or limbs.
Charles Darwin
Much of Darwin's theory of evolution was developed on his Voyage of the Beagle in 1831. While traveling on the ship the Beagle, Darwin observed different species of animals and how they were uniquely adapted to their environments. Darwin theorized that these adaptations came about through the process of natural selection. According to Darwin's natural selection, when animals have traits which suit them to survival, they are more likely to live long enough to produce offspring who will inherit and exhibit those same traits.
In the book The Origin of Species, Darwin explained natural selection and described the concept of descent with modification. Darwin wrote that different species of an animal descend from a common ancestor, which is why species of the same animal have common traits. Different species of animals have different modifications, or adaptations because of natural selection.
Evolutionary Theory Today
Knowledge of genetics and an overwhelming body of scientific research has supported Charles Darwin's early ideas of evolution. Experiments with rapidly reproducing species of animals, bacteria and viruses have demonstrated the validity of natural selection. Additionally, carbon dating techniques have shown that fossils are billions of years old.
The wealth of evidence for evolution has lead contemporary scientists to focus on different types of natural selection and the myriad of forces driving evolution. Efforts to better understand organisms by their evolutionary relationships has revitalized the way scientists name and classify all life forms. New evolutionary research has lead to important medical discoveries, such as the treatment of drug resistant viruses, and how to better prevent and treat genetic disorders.
Resources
Baylor.edu. "How Old Are the Oldest Fossils?" (Accessed February 14, 2011).
Berkeley.edu "Relevance of Evolution: Medicine." (Accessed February 14, 2011).
Caltech.edu. "How Old is Earth?" (Accessed February 14, 2011).
Campbell, Neil and Jane Reece, Lisa Urry et al. Biology, 8th ed. Pearson Education. 2008.
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