Baculum (Penis Bone)

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Absolute Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
MOCA Topic Authors: 

Great apes have a baculum (penis) bone (a small bone situated near the tip of the penis between the urethra and corpus cavernosum) and humans do not. The evolutionary reasons and the genetic basis for this difference are unknown. One possible function of the baculum is protection of the urethra.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
6,000 thousand years ago
Probable Appearance: 
2,000 thousand years ago
Definite Appearance: 
100 thousand years ago
Related MOCA Topics
Referenced By:
Topic Certainty
Penis Size and Morphology


  1. Postcopulatory sexual selection influences baculum evolution in primates and carnivores, Brindle, Matilda, and Opie Christopher , Proceedings of the Royal Society B: Biological Sciences, 2016/12/14, Volume 283, Issue 1844, (2016)
  2. The evolution of human reproduction: a primatological perspective., Martin, Robert D. , Am J Phys Anthropol, 2007, Volume Suppl 45, p.59-84, (2007)