Darwin is accredited with the theory of evolution, or descent with modification, which states that a species adapts to its environment over time. These changes occur within a population. Darwin explained that these changes within a population occurred because of natural selection. Natural selection is the process in which organisms that have traits that are favorable for an environment survive. Thus, these organisms are more likely to find a mate and pass their genetic material onto future generations (this is the biological definition of being fit). Likewise, those with less advantageous traits would perish due to the pressures exerted upon them from the environment (not having the right covering for the temperatures of the environment, not being camouflaged, etc).
Darwin traveled around the world on a ship called the HSM Beagle. It was during this voyage that Darwin made most of his observation that lead him to the above theories. Darwin's theory of evolution by natural selection can be explained through the following four observations:
1. There are variations amongst individuals within a population of a species.
2. Traits are passed on from one generation to another (from parent to offspring).
3. Populations can produce more offspring than the environment can sustain. This leads to competition amongst the offspring.
4. Due to a lack of resources in the environment, some individuals of the population will not survive, and those who do will pass on more offspring.