Essay on Darwin's Theory of Evolution by Natural Selection
Darwin's Theory of Natural Selection says that nature selects organisms with the best features for survival, while getting rid of inferior species. Natural selection is how we get new species from existing ones. Components of this theory include over reproduction, variation, competition, survival of the fittest, inheritance and adaptation.
Many species have more offspring every year than the environment they live in can support. This is called over reproduction. The high rate of growth results in a struggle for the resources they need to survive and a higher mortality rate within this species.
In every species there is variation. Even brothers will vary in color, height, and weight. There are other variations such as the number of limbs or the number of eyes that do not vary as often. Some populations show more variation than others. A good example is the Galapagos Islands that are geographically isolated and show more variation and species evolve very distinct characteristics.
Most organisms have variations, some do not affect survival like eye color in humans, but some improve the chances of survival. A rabbit that runs faster than all the other rabbits is more likely to escape predators. Algae that are more efficient at getting energy from the sun will grow faster. Over time a fast rabbit will breed with other fast rabbits and their children will be even faster. This is an example of survival of the fittest.
Traits that give individuals a reproductive advantage can be passed from parent to child. Even if the reproductive advantage is very small over time and many generations the advantage will become stronger and stronger. Some species have traits that are strongly influenced by inheritance.
Beneficial mutations and adaptations remain in organisms because they aid in their survival. Beneficial mutations are passed on from generation to generation and overtime the result is an entirely different organisms. One example of adaptation is the turtle population who ate food that was loaded the ground and had short legs and straight shells. When the turtles moved to another island and the food source was much higher up only the turtles with longer legs survived. Over many years their necks and legs grew and their shells became rounded to reach the food. This is adaptation is natural selection.