Why Humans Have the Largest Penis Among All Primates: An RC Inspired by IIM Indore

I picked up Desmond Morris's The Naked Ape one afternoon and did not put it down until dark. Its opening observation is simple. Of the 193 living species of monkeys and apes, 192 are covered in hair. The exception is the naked ape, which has had the arrogance to name itself Homo sapiens. By the time Morris reached the chapter on sex, I was convinced I was reading one of the most honest books written about what human beings actually are.

Morris's argument about the human penis is precise. Humans are the only primates that walk upright. Upright posture made the genitalia permanently visible. A male gorilla, two to three times the weight of an adult man, has a penis between three and six centimetres when erect. A chimpanzee has a longer organ but one that is narrow and tapered, shaped entirely differently from the human penis, which is uniquely wide and prominent. Humans have the largest girth of any primate. Morris argued this was not an accident. Bipedalism created visibility, visibility created selection pressure, and what got selected evolved as physiological glue, a mechanism to keep couples together through the long separations that hunting-and-gathering demanded.

I found this convincing for about two years. Then I read the modern biology and discovered that Morris had done something even the best scientists occasionally do. He found a genuine pattern and explained it using the social values of the decade in which he was writing. The 1960s believed in monogamy, in the nuclear family, in the idea that men hunted and women stayed home. Morris's evolutionary story reproduced all of these assumptions and dressed them up as zoology.

Morris found a genuine pattern in nature and explained it using the social values of the decade in which he was writing.

A study published in PLOS Biology in January 2026 by researchers at the University of Western Australia, Monash University, and the Australian National University offers the modern consensus. Using 343 computer-generated male figures shown to more than 800 participants, it found that a larger penis made men more attractive to women and more threatening to other men simultaneously. The dual-selection hypothesis proposes two pressures rather than one. Female mate choice selected for size as a signal of genetic fitness. Male rivalry selected for size as a dominance signal that deters confrontation. Morris was not wrong that bipedalism drove the evolution. He was wrong about who was doing the selecting and why.

What troubled me more than the specific error was the pattern. The history of evolutionary biology is full of theories that map suspiciously neatly onto the cultural assumptions of the scientist proposing them. Victorian biologists found hierarchy everywhere. Mid-century Americans found the suburban family. Morris was meticulous. The worry is that the framework through which a scientist interprets data is itself a product of the culture that produced the scientist, and no amount of rigour fully compensates for this.

Morris died in April 2026 at ninety-eight, months after the PLOS Biology study appeared. He was right about the mechanism. He was wrong about the motive. The Naked Ape remains one of the most important books written about the human animal in the twentieth century, not because Morris got everything right, but because he asked questions most scientists in 1967 considered too undignified to ask. The answers have changed. The questions were always worth asking.