In the vast and varied animal kingdom, the human penis stands out for its remarkable lack of flair. According to a leading anatomist, our anatomy is surprisingly 'conservative' when compared to the spiked, corkscrewed, and even detachable members found in other species.
The Competitive World of Animal Mating
Professor Michelle Spear, an anatomy expert at the University of Bristol, explains that this diversity in the animal world is driven by one key factor: sperm competition. This occurs when multiple males mate with the same female, and their sperm must compete internally for the chance to fertilise an egg.
In this high-stakes environment, the penis has evolved into a 'competitive tool.' For instance, the domestic cat possesses a penis with backward-facing spines. These spines serve a dual purpose: they stimulate ovulation in the female and make withdrawal painful, discouraging her from mating with other males shortly after.
The strategies can be even more extreme. A 2001 study revealed that male bedbugs practise traumatic insemination, using a dagger-like penis to stab through the female's abdominal wall to deposit sperm. Meanwhile, some species of male ducks have evolved corkscrew-shaped penises that can extend in under half a second. This is a direct counter to female ducks, which have developed highly convoluted vaginas with dead-end pockets to exert control over fertilisation.
Why Human Anatomy Took a Simpler Path
In stark contrast to this wild competition, human mating rituals are generally less competitive and more focused on pair-bonding. A man and woman tend to be together when trying for a baby, reducing the intense pressure for males to outcompete rivals directly.
As a result, humans have not developed extreme penile features such as bones, known as a baculum, or backward-facing spines. The baculum, found in mammals like dogs, chimps, and walruses, provides structural support, allowing for prolonged mating—a distinct advantage in a competitive race to inseminate.
'The human penis is so uniform, it's an anatomical outlier,' Professor Spear states. Our species' tendency towards monogamy means men historically haven't needed such specialised tools to compete for a partner.
The Evolutionary Journey of the Penis
Ultimately, penises first evolved as a practical solution to a fundamental problem: how to achieve internal fertilisation on land. Professor Spear notes that while ancient aquatic animals could simply release sperm and eggs into the water, terrestrial life required a new mechanism to transfer sperm directly into the female body.
While the human penis may be conservative in shape, it is not lacking in size compared to our closest relatives. The average erect human penis measures 5.1 inches (13cm). This is larger than a chimp's or bonobo's 3.1 inches (8cm), an orangutan's 3.3 inches (8.5cm), and significantly larger than a gorilla's 1.25-inch (3cm) member.
Simon Underdown, a professor of biological anthropology at Oxford Brookes University, suggests that the human penis size is 'almost certainly' related to our evolution into bipedal creatures who walk on two legs. This anatomical development may have played a role in making humans 'king of the swingers' in this particular regard.
