The missing human baculum: a victim of conspecific aggression and budding self‐awareness?

Abstract

AbstractUnlike most primates and all other great apes, humans Homo sapiens do not possess a baculum (penile bone). I discuss the shortcomings of previous hypotheses to explain the loss of the baculum, argue that they fail to explain it fully, and show that the evolutionary history of this loss remains enigmatic. I also propose a new hypothesis: that conspecific aggression, in combination with the development of self‐awareness, may have played a role in the loss. If the presence of a baculum exacerbated the prevalence and severity of penile injuries resulting from blunt trauma to a flaccid penis, increasing ability to foresee the consequences of their actions would also enable hominins to realise that these injuries are a useful tool in male–male competition. This behavioural innovation, planned conspecific aggression with the goal of temporary exclusion of competitors from the breeding pool, would create an environment in which a genetic mutation for a penis without a baculum (or with an unossified baculum) would strongly increase the fitness of the mutant phenotype. Along with the hominin propensity for social learning and cultural transmission, this hypothetical scenario may explain why this phenotype became fixed in all human populations.