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12. Human males do not not have a bone in their penis like male chimps (and many other mammals) do.

The baculum

What is a baculum?

The baculum (os penis) is a bone found within the penis of certain mammals, including many primates, rodents, bats, carnivores, and some insectivores. It is an isolated bone, derived from connective tissue and located at the distal end of the penis, above the urethra. Lower mineral density and reduced stiffness of the baculum compared to skeletal bones may help reduce the risk of fracture under strain during copulation, although breakage can sometimes occur.

You mentioned primates, do we humans have such a bone?

No, human males don’t have a baculum! This is surprising because all other apes and Old World monkeys have one, despite a trend towards reduced size of the baculum among the great apes. As fossil primate bacula are extremely rare, it is unknown when the baculum was lost within the hominid lineage. And despite some speculation relating to upright posture and changing mating strategies, why human males lack a baculum remains enigmatic.

What does it look like?

A particularly striking characteristic of the baculum is its extreme anatomical diversity. Bacula of different species come in a multitude of forms, with variation in their length, thickness, curvature and complexity of shape (Figure 1). The baculum can also be small or large relative to body size, reaching more than 60 cm in the walrus, Odobenus rosmarus. More complex forms may feature bizarre looking teeth or digit-like projections, including components that protrude from the glans penis in certain rodents. Such diversity of form makes the baculum a particularly useful feature for species identification and taxonomy.



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