section_path: Effects/On diversity
section_name: On diversity
paragraph_text: On diversity
  
  Domesticated ecosystems provide food, reduce predator and natural dangers, and promote commerce, but their creation has resulted in habitat alteration or loss, and multiple extinctions commencing in the Late Pleistocene.
  
  Domestication reduces genetic diversity of the domesticated population, especially of alleles of genes targeted by selection. One reason is a population bottleneck created by artificially selecting the most desirable individuals to breed from. Most of the domesticated strain is then born from just a few ancestors, creating a situation similar to the founder effect. Domesticated populations such as of dogs, rice, sunflowers, maize, and horses have an increased mutation load, as expected in a population bottleneck where genetic drift is enhanced by the small population size. Mutations can also be fixed in a population by a selective sweep. Mutational load can be increased by reduced selective pressure against moderately harmful traits when reproductive fitness is controlled by human management. However, there is evidence against a bottleneck in crops, such as barley, maize, and sorghum, where genetic diversity slowly declined rather than showing a rapid initial fall at the point of domestication. Further, the genetic diversity of these crops was regularly replenished from the natural population. Similar evidence exists for horses, pigs, cows, and goats.