Grown since 1997 in the United States and Canada, 86% of the US corn crop was genetically modified in 2010. Most historians believe corn was domesticated in the Tehuacan Valley of Mexico. Maize spread to the rest of the world because of its ability to grow in diverse climates. The corn plant is often 2.5 m (8 ft) in height, though some natural strains can grow 12 m (40 ft). Sexual reproduction, basically each year, randomly selects half the genes from a given plant to propagate to the next generation.