Evolution “is a process that results in heritable changes in a population spread over many generations” (Moran). There are many different definitions for the word “evolution,” such as biological, stellar evolution… The definition that will be discussed is biological evolution. “Biological (or organic) evolution is change in the properties of populations of organisms or groups of such populations, over the course of generations” (Moran). Evolution can be put into two categories: macroevolution and microevolution. “Macroevolution is used to refer to any evolutionary change at or above the level of species” (Wilkins). That is that it occurs over a long period of time, producing major changes in species. “Microevolution refers to any evolutionary change below the level of species, and refers to changes in the frequency within a population or a species of its alleles (alternative genes) and their effects on the form, or phenotype, of organisms that make up that populations or species” (Wilkins). That is that minor changes occur within a small species or group of organisms within a short period of time. There are many mechanisms of evolution such as: genetic variation, drift and selection, natural selection, and speciation. Genetic variation has two processes recombination and mutation. Recombination is when the genes from two parents are mixed to produce offspring by sexual reproduction. Mutation happens when DNA is copied wrong during replication which leads to a difference between the parents gene and the offspring’s gene. Sometimes the mutation causes a huge difference but sometimes it does not. Drift and selection are random varieties in gene frequency, only scene at the level of DNA. Natural selection was discovered by Charles Darwin and it is when the same organisms adapt to different environment, making the same organism appear different from each other.