Genetic variation is increased by gene mutations. DNA does not always reproduce exactly. Rare changes occur, and these changes can be inherited. Many changes in DNA cause faults; some are neutral or even advantageous. This gives rise to genetic variation, which is the seed corn of evolution. Sexual reproduction, by the crossing over of chromosomes during meiosis, spreads variation through the population. Other events, like natural selection and drift, reduce variation. A population in the wild always has variation, but the details are always changing.p90