Bold chickens, bigger chickens
What happens when birds are domesticated? Study shows that domestication makes chickens larger. When selected over multiple generations for reduced fear towards humans, red junglefowls (ancestors of domestic chickens) grew faster and larger, laid larger eggs, and had more efficient metabolism than the fearful counterparts. The tamed birds had higher serotonin molecules, which are involved in fear and metabolism. Researchers concluded that domestication likely correlates to favorable traits via serotonin increase. They are now looking at genetic basis of these changes in bold, tamed fowls.
Is domestication driven by reduced fear of humans? Boldness, metabolism and serotonin levels in divergently selected red junglefowl (Gallus gallus)
Biology Letters (2015)