hahahha the bonobos story, well some animals eat their own crap also , do cannibalism and other stuff so we will learn from animals and soon that may constitute normal too , no ? dont know how stupid people giving examples of bonobos can discount that HIV virus that causes AIDS is present in primates also , transmission of that virus does not kill monkeys but it kills Human being , what works for the monkey may not work for you.
Apart from HIV , those men who indulge in act of same sex have higher occurrence of following diseases
condyloma acuminata,hemorrhoids, nonspecific proctitis, anal fistula, perirectal abscess , anal fissure, amebiasis , benign polyps, viral hepatitis , gonorrhea, syphilis, anorectal trauma and foreign bodies, shigellosis , rectal ulcers and lymphogranuloma venereum
In the end , there is nothing 'natural' about this act