Natural Selection
Evolution, the change of species over time, is the central unifying theme of biology. Biological evolution occurs through natural selection. Natural selection is the result of overproduction of offspring having variations, these variations struggling for survival, and the subsequent survival and increased reproduction of those best adapted to a particular environment. 

Mutations
One source of the variation driving the process of evolution is mutation. Mutation is the change in DNA of an organism which may result in that organism being different than its parents. While there are many causes of mutations, some factors are known which rapidly increase the incidence of mutation.

The differences in species produced by mutation is a driving force in the process of natural selection.

Variation
Variations are differences between groups of organisms of one species. Mutation is one source of variation between different groups within a species. The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.

This page and the links at the left are designed to aid students in reviewing the following  topics which will appear on the New York State Living Environment Regents Examination: natural selection, mutation, and variation in living things.    In addition, students may test their knowledge of the material presented here by accessing multiple-choice questions from past Regents Exams.