Whydowelaugh?Foryearsscientistshaveaskedthemselvesthisq...
问题详情：Whydowelaugh?Foryearsscientistshaveaskedthemselvesthisquestion.Noanimalslaughandsmile–onlyhumanbeings,sodoeslaughinghelpustolivelonger?Theanswerseemstobethatsmilingandlaughinghelpustobecomeca...