i covered this topic in a class in university way back in the caveman days they would sit around the fire with their half wild dogs stroking their fur elicited the guard guard guard instinct in the animal thats the theory anyways so basically the theory is we were able to relax knowing we were protected   
ගුහා මිනිසාගේ කාලයේ දී මම මෙම මාතෘකාව විශ්ව විද්‍යාලයේ පන්තියකදී ආවරණය කළෙමි අපි ආරක්ෂා වී ඇති බව දැන විවේක ගැනීමට   