why do guys like girls with big boobs and ass

the definition of sexy is surprisingly well defined all over the world .. it has been changing off late but still a girl with curves (big boobs small waist) is the most common standard for sexy

there is a hormone called progesterone which is vital for female pregnancy .. helps in maintaining menstrual cycles and supports gestations .. there is another hormone called estradiol which helps in development of sexual organs (supports vagina lining etc) ..  now it has been researched and found out that the the girls with a high ratio of boobs to waist would have as much as 3 times of these hormones than other girls .. 

us humans had obviously figured it long time back by trial and error .. the guys figured out that if he could find a mate with a high ratio of breast to waist, his odds of procreating would go up a lot .. this was learnt by human males over 100s and 1000s of generations and has become a part of the way guys think now without anyone having to tell them .. 

and thats why a guy would get attracted to a "hot girl" with big boobs / ass and small waist :)