Scientists have discovered why humans do not have a penis bone, unlike chimpanzees , bears and most other mammals. Primates who mate for three minutes or more tend to have far longer penis bones than those whose intromission, or vaginal penetration, is below three minutes, she said. In contrast, the aye-aye , a nocturnal lemur, copulates for around an hour at a time and has a very long baculum. Ms Brindle said longer penis bones were also seen in species with seasonal breeding and polygamous mating systems, which humans generally do not have. Other reasons for the lack of baculum in humans is that the human mating system takes place throughout the year and is less competitive than that of other animals. Chimpanzees, who only have sex for around seven seconds at a time, have a very small baculum, suggesting that there might be evolutionary pressure among apes to lose the penis bone. You can find our Community Guidelines in full here. Want to discuss real-world problems, be involved in the most engaging discussions and hear from the journalists?
Register for an account
Humans have a much longer and wider penis than the other great apes. Even the largest of gorillas, more than twice as heavy as a human, will have a penis just two and half inches long when erect. However our testicles are rather small. The relative size of our penis and testes is all down to our mating strategies, and can provide some surprising insights into early human culture. Primates exhibit all sorts of mating behaviour, including monogamous, polygynous — where males have multiple mates — and multimale-multifemale. One indicator of which behaviour occurs in a species is the size difference between males and females.
All rights reserved. This picture of two mating insects comes with an unexpected twist. The one on top is a female, and she has a penis. The one on the bottom is a male, and he has the equivalent of a vagina. During sexual bouts that can last for 40 to 70 hours , she penetrates him and uses her genitals not to deliver sperm, but to collect it. The 3-millimetre-long species is called Neotrogla curvata , and it lives in Brazilian caves. There are four Neotrogla species and the females all have penises.