Spanking the Monkey

October 4, 2010

Torah Kachur

Charming the Snake.  Choking the Chicken.  Freeing Willy.  The amount of slang for masturbation with animal references should be seriously disconcerting.  Except that a wide-range of animals including dogs, cats, horses, all apes, lions, bears... and the list goes on...  have been found to Jack off.  Included on the list are elephants, donkeys and walruses that manage to flog the bishop with their fins.  Even birds have been shown to rub their cloaca against pretty much anything.

This phenomenon isn't restricted to males either - female organgutans were observed exhibiting inspiring creativity by fashioning home-made dildos from lianas.  Female horses during breeding season will rub up against fence posts, barn doors and seemingly anything made of wood.

Discovering that a species can milk the moose is fun and entertaining and often awe-inspiring.  You have to respect a macaque for committing 1-6% of its daily metabolism to producing ejaculate and the ability for 'self-directed oral sex' in a variety of mammals.  But the bigger question is why?  If masturbation is so widespread among all animals then it must provide an evolutionary advantage. 

A new study  has found ground squirrels can be added to the list of those that shake hands with the devil.  Previous explanations to this blatant waste of sperm in and around a females oestrus period were that masturbation provided a way to display fertility to potential mates or as a deterrant to rivals. 

In contrast, it was also thought that masturbation could provide a sexual release or as a way to refresh sperm.  Studies done on the ground squirrles of Namibia concluded that masturbation was likely used as a method of cleansing the genitalia.   This is likely species dependent when genitalia are more accessible to the environment and likely to be dirtier.  In other words, they kept clean by getting down and dirty.

For most animals, the more likely reason for whacking off is that sperm quality improves the more a man pleasures his loins - a recent study suggests that daily masturbation and ejaculation can reduce the amount of accumulated DNA damage in sperm by 12%.  Therefore wasting sperm into a sock can actually improve the mobility of sperm and increase fertility.  A continuation of this theory is the idea of sperm competition. This is when sperm from multiple males have a race to the egg and undergo various forms of chemical competition to see who gets to be the lucky shizz.  Most women likely don't have sex with multiple males during their ovulatory phase... we aren't like the chimpanzee, where a single female chimp was observed to have sex with 50 male partners in a single day (ouch). 

One consequence of shining the pole so often is that the testis enlarges to accomodate the demand for sperm.   It's personal preference if this is desirable but there may be an evolutionary significance to larger balls.  And that is the biggest balls gets the worm.  There is precendent amongst several different species, including our ape cousins, that larger testes actually attract mates. Though it is unlikely that larger ball size relates to the desirability of a human male as most men don't go around showing off their packages. 

The idea of refreshing sperm seems to account for the evolution of masturbation from turtles to donkeys.  It is unclear if these species have hairy palms.

Follow Science in Seconds by Facebook /Twitter /Email.

_{Waterman, J. (2010). The Adaptive Function of Masturbation in a Promiscuous African Ground Squirrel PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0013060}