Introduction to Darwin's Theory of Evolution

The Theory of Evolution: 

Natural Selection and Survival of the Fittest The Theory of Evolution

Natural Selection: 

Darwin proposed a mechanism for evolution. Though the idea that life evolved was first proposed by Lucretius over 2000 years ago, Charles Darwin, a 19 th century naturalist, codified and published the first scientific treatise on the subject. In 1831, one of Darwin’s professors at Cambridge, recommended him for the position of naturalist on the research vessel, HMS Beagle. Natural Selection

Science Before Darwin: 

In Darwin’s time, most people held the view that each species was a divine creation that existed unchanged since the creation of the Earth. In 1809, a French scientist, Jean Baptiste Lamarck proposed the hypothesis that organisms change over time and generations. Lamarck believed that over time, physical features either increased or decreased in size according to use. He believed that these increases or decreases were passed on to following generations. Science Before Darwin

Darwin’s Observations: 

During his voyage, Darwin observed many phenomenon that led him to believe that species were not unchanging but that over time species changed slowly based on heredity, environment, and mutation. For example, Darwin found, in one area of South America, fossils of extinct armadillos that were similar to but not identical to armadillos found in the same area during his visit. Rather than believing that he had found two different but similar species, he decided that the current armadillos must be of the same species but slightly evolved from the fossils he had found. Darwin’s Observations

Galapagos Island: 

On the Galapagos Islands, Darwin was struck by the number of organisms that were similar to, but not exactly like, the species on the near by coast of South America. Darwin’s explanation was that species from the coast migrated to the island long ago and, over time, evolved into new species. Darwin called this process “descent with modification” or evolution. Galapagos Island

The Key: 

Darwin kept his ideas to himself for many years. He read an essay by an economist name Malthus that spurred him to publish. Malthus suggested that the human population was fully capable of increasing beyond its food supply. Population growth occurs at a geometric rate. Food supply growth tends to occur at an arithamatic progression. Malthus suggested that the human population growth was controlled by disease, warfare, and famine and these things kept us from over populating our environment. The Key

Darwin and Malthus: 

Darwin felt that Malthus’ theory could be applied to any population. Each organism has the potential to produce many offspring in its lifetime. In most cases, however, only a few individuals successfully breed and produce viable offspring. Darwin theorized that “Individuals whose physical or behavioral traits better suit their environments are more likely to breed and produce offspring than less well adapted organisms.” This is the fundamental theory of natural selection. Darwin and Malthus

Publication of Darwin’s Work: 

Darwin showed his theories to only a few scientists that he trusted. Recently published works on the same subject had been harshly criticized by the scientific community. Finally, a young man named Alfred Wallace sent a copy of his essay to Darwin in the hope that Darwin could help him get it published. Friends of Darwin arranged for a summary of Darwin’s findings to be presented along with Wallace’s work. Publication of Darwin’s Work

The Origin of the Species: 

Finally Darwin’s work was published under the title of “On the Origin of Species by Means of Natural Selection” in 1859. To say the least, many people were deeply disturbed, especially by his inference in later works that apes and man sprang from the same origins. The Origin of the Species

Darwin’s Justification: 

The following four points are what Darwin used to justify his theories: Variation exists within the genes of every population or species as the result of random mutation and translation error. In a particular environment, some individuals of a population of species are better suited to survive (as a result of variation) and have more offspring. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread through out that population. There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct. Darwin’s Justification