How does evolution occur

Genes are the portions of an organism's DNA that carry the code responsible for building that organism in a very specific way. Genes -- and, thus, the traits they code for -- are passed from parent to offspring. From generation to generation, well-understood molecular mechanisms reshuffle, duplicate, and alter genes in a way that produces genetic variation. This variation is the raw material for evolution. Learn More Evolution Since Darwin. Sexual reproduction allows an organism to combine half of its genes with half of another individual's genes, which means new combinations of genes are produced every generation.

In addition, when eggs and sperm are produced, genetic material is shuffled and recombined in ways that produce new combinations of genes. Sexual reproduction thus increases genetic variation, which increases the raw material on which natural selection operates.

Genetic variation within a species -- also known as genetic diversity -- increases a species' opportunity for change over successive generations. Learn More The Advantage of Sex. Evolution is not a random process. The genetic variation on which natural selection acts may occur randomly, but natural selection itself is not random at all. The survival and reproductive success of an individual is directly related to the ways its inherited traits function in the context of its local environment.

Whether or not an individual survives and reproduces depends on whether it has genes that produce traits that are well adapted to its environment. Learn More Life's Grand Design. Evolution and "survival of the fittest" are not the same thing. Evolution refers to the cumulative changes in a population or species through time. Natural selection works by giving individuals who are better adapted to a given set of environmental conditions an advantage over those that are not as well adapted.

Survival of the fittest usually makes one think of the biggest, strongest, or smartest individuals being the winners, but in a biological sense, evolutionary fitness refers to the ability to survive and reproduce in a particular environment.

Popular interpretations of "survival of the fittest" typically ignore the importance of both reproduction and cooperation.

To survive but not pass on one's genes to the next generation is to be biologically unfit. And many organisms are the "fittest" because they cooperate with other organisms, rather than competing with them. Learn More Adaptation and Natural Selection. Further Exploration Concept Links for further exploration synteny gene trait genotype Hardy-Weinberg equilibrium allele speciation Hardy-Weinberg equation population bottleneck species allele frequency natural selection genetic drift sexual reproduction neutral theory of evolution.

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