2.3+Genetics+-Evolution

==__What is Evolution?__ Evolution is the change in the gene pool of a population over a period of time. **1. It is possible for the DNA of an organism to randomly change, or mutate**. A mutation changes the DNA of an organism in a way that affects its offspring, either immediately or several generations down the line. The change brought about by a mutation is either beneficial, harmful or neutral. If the change is harmful, then it is unlikely that the offspring will survive to reproduce, so the mutation dies out and goes nowhere. If the change is beneficial, then it is likely that the offspring will do better than other offspring and so will reproduce more. Through reproduction, the beneficial mutation spreads. The process of culling bad mutations and spreading good mutations is called natural selection. **2. As mutations occur and spread over long periods of time, they cause new species to form.** Over the course of many millions of years, the processes of mutation and natural selection have created every species of life that we see in the world today, from the simplest bacteria to humans and everything in between.==

The forces of natural selection act on phenotypes, but only if there is a change in the genotypes of a population has evolution occurred.
 * Living things produce more offspring than the finite resources available to them can support.
 * Thus living things face a constant **struggle for existence**.
 * The individuals in a population vary in their phenotypes.
 * Some of this variation is inheritable; that is, it is a reflection of variations in genotype.
 * Those variants best adapted to the conditions of their life are most likely to survive and reproduce themselves ("survival of the fittest").
 * To the extent that their adaptations are inheritable, they will be passed on to their offspring.