Thursday, April 5, 2012

Evolution of Sex(ual organs)

Recently in class, we have learned about evolution of sex and sexual selections. For this mating to happen, individuals of different genders had to develop specific sexual organs to accomplish this ritual. As our blog theme focuses on evolution of appendages, I naturally was curious about the origin of penis.

I found two articles that had two different findings on the origin on penis.


This ABC News article proposed a 100 million years old evidence of the oldest penis from a fossil of an ostracod, an ancestral crustacean. And surprisingly, this fossil record revealed that they actually had two penises. 


This is another article from National Geographic stating that they found the oldest penis fossil record of a 400 million years old spider. 

What is surprising is that the National Geographic article was written in year 2003, whereas the ABC News one was written last year. I guess the ABC reporters do not really check upon literature... 

I didn't include any graphic photos on this blog, but here's an example of an ostracod male genital.

The top one is the female, and the bottom one represents a male ostracod. The region labeled as Hp is the penis in its relaxed mode. 

Next post, I will elaborate on evolution of human penis (without any graphic photos I promise) and in other vertebrates, as well as how they play an important role in sexual selection. 

Robin J. Smith, Takahiro Kamiya, David J. Horne. 2006. Living males of the 'ancient asexual' Darwinulidae (Ostracoda: Crustacea). Proceedings of the Royal Society B: Biological Sciences 273:1569-1578.


  1. What could be the benefit of having two penises? It's not like it increases your rate of copulation with a set number of females, right?

  2. two penises might be the product of an early bifurcation occured during development (like in humans). The trait (two penises) might not be representative of the original population. It was just a malformation concerning few of them.