Read The Whole Page FirstThe idea of evolution is a simple one. Things change. Right now we're just talking about the word, not the philosophical idea. The process of cars changing over the past 100 years can be thought of as an evolution in engineering. When an organism changes over many generations, it might be better suited to live, or more likely to die. To describe what happens, scientists have a few terms.
Natural SelectionWe were just talking about that. Sometimes you've got a skill that helps you survive; sometimes you don't. If you were a 500 pound bird with little tiny wings and little tiny legs, chances are you wouldn't move around too well. One day you might run out of food and die. Oh well, you were just selected for extinction.
Convergent EvolutionThis is when two totally different species develop similar traits. They have come up with the same solution to a problem but from different directions. It's not a conscious choice to develop an eye or a way of hearing. Outside natural factors create a situation where that skill is a benefit.
For example, you are a plant and I am an animal. We both have animals hunting us and eating us. We need protection. So we both develop spines to poke the hunters. The spines are made in different ways but do the same job. You are a cactus and I am a porcupine.
Divergent EvolutionThis is when your development starts at one place and splits in different directions. We start as the same species, but then as more generations develop, my group becomes good at one thing and yours at another.
Bird beaks are a good example for this one. One species of bird can develop in different directions depending on what type of food it eats. Their beaks develop different shapes after many generations. Charles Darwin used bird development in many of his scientific papers.
CoevolutionThis is when two different species change and evolve over time together. They are usually dependent on each other for survival. Flowers and insects are good examples of this type of coevolution.
If you have seen really fancy orchids, they often depend on a single species of bug to help them reproduce. As one species changes, the other will make mirror changes so that it can continue to survive.
Our World: Finding Dinosaurs (NASA eClips Video)
Encyclopedia.com (Natural Selection):
Wikipedia (Natural Selection):
Encyclopædia Britannica (Natural Selection):