While certain temperament differences may sometimes play a role, there's no actual proven theory that says one is more affection or friendly than the other. (fourleggedguru.com)
Different parenting strategies appear to work better for children with certain temperaments. (child-encyclopedia.com)
Temperament is innate and has been characterized in various ways by different researchers — in other words, babies have certain temperaments naturally, but temperament is not their «personality.» (verywellfamily.com)