We're hydraulic.
"The evolutionary biologist Richard Dawkins speculated in 2006 that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is a result of sexual selection by females looking for signs of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function betrays not only physical states such as diabetes and neurological disorders but mental states such as stress and depression.[6]
It has also been speculated that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is because humans evolved a mating system in which the male tended to accompany a particular female all the time to attempt to ensure paternity of her children which allows for frequent matings of short duration.
Observation suggests that primates with a baculum only infrequently encounter females, but engage in longer periods of copulation which the baculum makes possible, thereby maximizing their chances of fathering the female's offspring. For humans, it is almost impossible to tell when the female is fertile so frequent matings would be necessary to ensure paternity."
*****” For humans, it is almost impossible to tell when the female is fertile..............(so frequent matings would be necessary to ensure paternity”)**********
Try looking for PMS symptoms....... - then mating would only be necessary once a month for procreation......
•Symptoms start sometime after ovulation, which occurs about two weeks before the start of a period. Typically, symptoms occur during the five days before a period. However, some women have symptoms for two weeks or so leading up to a period. Typically, symptoms gradually get worse as the period approaches.
•Symptoms go within three to four days after your period starts.
•Symptoms that occur all the time are not due to PMS.
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http://www.patient.co.uk/health/Premenstrual-Syndrome.htm
“Snipe pines for the penis spine.”
- Epsin