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. so a population in the wild always has variation, but the details are always changing.p90