Domestication syndrome

Domestication syndrome refers to two sets of phenotypic traits that are common to either domesticated plants or domesticated animals.

Domesticated animals tend to be smaller and less aggressive than their wild counterparts; they may also have floppy ears, variations to coat color, a smaller brain, and a shorter muzzle. Other traits may include changes in the endocrine system and an extended breeding cycle. These animal traits have been claimed to emerge across the different species in response to selection for tameness, which was purportedly demonstrated in a famous Russian fox breeding experiment, though this claim has been disputed.

Other research suggested that pleiotropic change in neural crest cell regulating genes was the common cause of shared traits seen in many domesticated animal species. However, several recent publications have either questioned this neural crest cell explanation or cast doubt on the existence of domestication syndrome itself. One recent publication points out that shared selective regime changes following transition from wild to domestic environments are a more likely cause of any convergent traits. In addition, the sheer number, diversity, and phenotypic importance of neural crest cell-derived vertebrate features means that changes in genes associated with them are almost inevitable in response to any significant selective change.  

A significant aspect of domestication syndrome is prolonged juvenile behavior/traits. A universal problem with the keeping of Tame Wild animals is the eventual, inevitable adulthood and behavioral difficulties thereof. Toy breed animals may be considered the furthest extreme aspect of this, as they are essentially, through size, human use & behavior, juveniles their entire lives (to the point where breeding them is a complex, delicate matter, and survival of the infants is lowered). One of Michael Crichton's final novels, NEXT, which featured gene/life form alteration in a great degree, even for his work, includes the tagline (and for the characters In the book, a presumable selling point) Permanent Puppies, on the dust jacket.

The process of plant domestication has produced changes in shattering/fruit abscission, shorter height, larger grain or fruit size, easier threshing, synchronous flowering, and increased yield, as well as changes in color, taste, and texture.