section_path: Animals/Desirable traits
section_name: Desirable traits
paragraph_text: Desirable traits
  
  The domestication of animals is the relationship between non-human animals and humans who have an influence on their care and reproduction. In his 1868 book The Variation of Animals and Plants Under Domestication, Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits and unconscious selection, in which traits evolve as a by-product of natural selection or from selection on other traits.
  
  There is a difference between domestic and wild populations; some of these differences constitute the domestication syndrome, traits presumed essential in the early stages of domestication, while others represent later improvement traits. Domesticated animals tend to be smaller and less aggressive than their wild counterparts; other common traits are floppy ears, a smaller brain, and a shorter muzzle. Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations.
  
  Certain animal species, and certain individuals within those species, make better candidates for domestication because of their behavioral characteristics: