Drawing from Ruse and McClellan, on what previous theories, biological and otherwise, did Darwin draw in developing his theory of natural selection?

 

Darwin is the father of evolution. In truth, Darwin arrived at his theory of evolution at the same time another scientist, Alfred Russell Wallace, came to the same conclusion. However, Darwin was a respected scientist even before he wrote On the Origin of Species, while Wallace was relatively unknown, so people were more inclined to listen to Darwin.

did Darwin draw in developing his theory of natural selection?

Darwin's theory consisted of two main points; 

1) diverse groups of animals evolve from one or a few common ancestors; 

2) the mechanism by which this evolution takes place is NATURAL SELECTION 

Darwin's theory of evolution, also called Darwinism, can be further divided into 5 parts,

1. Evolution as such - Darwin supported the ability of species to change over time

2. Common descent - Darwin felt that all of the diversity of life on earth emerged out of the evolution from one or a few common ancestors

3. Gradualism - Darwin felt evolution was a much slower process, taking place in innumerable small steps. 

4. Population speciation - This portion of Darwin's theory states that within a population, change in a species occurs as the balance of hereditary characteristics shifts across that population.

5. Natural selection - Natural selection is often called the most unique part of Darwin's theory. Competition, also called the struggle for life, had been thought of as a reason that a given species might succeed or go extinct, but Darwin extended the understanding to change within a species. Example, when a giraffe is born with a longer neck than its fellows, it gains an advantage because it is able to reach more food. The long-neck giraffe is therefore stronger, lives longer, and more likely to have offspring. These offspring are born with the same long neck as their parent, though some might have even longer necks. The cycle continues. 

*The theory of natural selection depends on five postulates:

- Individuals are variable.

- Some variations are passed down.

- More offspring are produced than can survive.

- Survival and reproduction are not random.

- The history of earth is long.

"On the Origin of Species"

Charles Darwin had the opportunity to study the wildlife of the Galapagos Islands. He was amazed by the great diversity of life. He hypothesized that there must be some process that lead to such diversity and adaptation. After returning from his voyage, Darwin put his thought in writing in a 490-page "abstract" that he entitled On the Origin of Species. He published the book in 1859.

The public reception of Origin was phenomenal. However, the mechanism of natural selection remained difficult to accept at the time because there were many points Darwin himself admittedly could not explain. For example, he knew that traits were passed down from parents to offspring, but he did not know how this happened. It was not until the early 1900's, when the field of genetics became the focus of intense study that Darwin's mechanism of natural selection received more intense scrutiny and deeper scientific support. With the discoveries of genetics, Darwin's theories gained a scientific basis beyond observation and were consequently accepted as a plausible mechanism for evolutionary change. Even before genetics arrived on the scene, the idea of "survival of the fittest" captured the imagination of the public. The idea was applied to everything from the business world to the structure of society as a whole.