DARWIN’S EVOLUTION THEORY

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 DARWIN’S EVOLUTION THEORY

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• Darwin’s revolutionary theory was that new species arise naturally by a process of evolution, rather than having been created by God (Creationism)
• In his "On the Origin of Species", Charles Darwin accepted the principle of the "inheritance of acquired characteristics" as a key factor in evolution
• Charles Darwin wrote this in 1859 - "The theory of evolution by natural selection"
• It is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits
• Logic is that changes that are good for an organism to adapt to its environment will help it survive and have more offspring
• This theory of "Evolution by natural selection" is found correct through evidence in paleontology, geology, genetics and developmental biology
• Two main aspects - 

1. All life on Earth is connected and related to each other
2. This diversity of life is a product of "modifications of populations by natural selection, where some traits were favoured over others

• Misleading term - To call this "survival of the fittest" is misleading, because fitness is not about being "strongest, fastest, tallest"
• Actually "fitness" refers to the ability to survive and reproduce
• Five parts of Darwin's theory - Darwin's theory of evolution (Darwinism) is into 5 parts: 

1. "evolution as such"
2. common descent
3. gradualism
4. population speciation
5. natural selection

• "Evolution as such" - Darwin supported the ability of species to change over time. That itself was a radical idea, given strong religious bias against it
• Common Descent - All the diversity of life on earth emerged out of the evolution from one or a few common ancestors. So it implied a less important role for humans as merely one of many branches in the animal world rather than a privileged species
• Gradualism - Lamarck felt that species-wide change could happen in a few generations, but Darwin felt evolution was a much slower process, taking place in innumerable small steps. So he estimated the world to be much older than contemporary geological theories accounted for.
• Population Speciation - Within a population, change in a species occurs as the balance of hereditary characteristics shifts across that population. (Lamarck said that each individual in the population must undergo the same change). So all giraffes living under tall trees would not necessarily develop long necks, but some would randomly be born with long necks, and then this hereditary trait would gradually spread throughout the population.
• Natural selection - Normally "Competition" or struggle for life was thought as the reason that a given species might succeed or go extinct. Darwin extended the idea to change within a species. 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 may be born with the same long neck as their parent, though some might have even longer necks. The cycle continues. 

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