The theory of evolution, as set forth by Charles Darwin in 1859, stated that all plant and animal life evolved over long periods of time from simple to more complicated forms through mutation and adaption. He also taught that only the fittest on each species would survive. This concept is called "Evolution by Natural Selection". Natural selection is that the strongest survive and propagate and therefore increase in the strength of the species.
On the Galapagos Islands, the various species established themselves and determined territories. Evolution then set in and many unique species, such as Darwin's finches, resulted. These finches probably descended from one type of ancestor and then, due to isolation and through chance, different climates and natural forces such as food availability and type, they evolved into thirteen different types of finches. So in short, based on the food availability and types, certain fiches survived. The process of their evolution would probably have began with immigrates from the mainland.
As they dispersed to different islands, new populations would be formed. Every time these satellite populations dispersed, there would be greater differences between the individual species.
Natural selection works as follows:
1. Variations exist in any population.
2. In and generation there are individuals that do not reach maturity and reproduce. Their characteristics are removed (passed on)
3. The organisms that survive to reproduce are best adapted to that environment as they have the variations that allowed them to survive (Survival of the fittest)
4. These favourable variations are passed onto the next generation, which become more and more common.
Some evidences of evolution include:
The Age of the Earth
Evolution can only take place over enormous periods of time. The fact the Earth has been dated 4,500 million years old which allows evolution to be possible.