This essay is about evolution, how why and when.

Essay by CaJoDeJayJunior High, 9th grade February 2003

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What Is Evolution?

Biological evolution refers to the changes that occur in a population over time. These changes are produced at the genetic level as organisms' genes mutate and/or recombine in different ways during reproduction and are passed on to future generations. Sometimes, individuals inherit new characteristics that give them survival and reproductive advantages in their local environments. These characteristics tend to increase in occurrence in the population, while those that are harmful decrease in frequency. This process of making more of the best and getting rid of the worst is known as "natural selection" or "survival of the fittest". Some people think that any change in an organisms' body or genetic makeup is evolution. However, this is not true. Non-genetic changes that occur during an organism's life span, for example increases in muscle tissue due to exercise cannot be passed on to the next generation and are not examples of evolution.

Are all species related?

Yes. Scientists today believe that all organisms share an ancestor somewhere in their history. When this theory is put into a chart it looks much like a tree. Therefore scientists have named this "chart" the "Tree of Life". Every branch of the "tree" represents a different species, and everywhere the branch forks or splits represents the common ancestor that binds two species together.

How do organisms evolve?

Individual organisms don't evolve. Populations evolve. Because individuals in a population vary, some in the population are better able to survive and reproduce given a particular set of environmental conditions. These individuals generally survive and produce more offspring, thus passing their advantageous traits on to the next generation. Over time, the population changes.

What do genes have to do with evolution?

First of all, to understand what genes have to do with evolution you must understand...