(Don't worry- no graphic pictures included)
In my previous post, we looked at two postulates for the earliest penis fossil records (up to 100~400 mya). Although the idea of males having sexual organs that stick out seems like an evolutionarily plausible and reasonable thing, for some animals, this seems quite extravagant and unnecessary. A specific example of this is birds. Only 3% of the bird species have penises. Knowing that having penis is the minority, the right question we can ask is: why do some birds have penises in the first place, and how are they different?
An article from Nature demystifies this phenomenon through observing ostrich penis.
Most penises become erect by blood vascular system, where the arteries become dilated that draws blood towards the penis. However, ostriches and other ratites, or flightless birds such as kiwis, utilize lymphatic system to achieve this erection. They have paralymphatic bodies below the muscle that cause erections. The origin of lymphatic erection is yet to be determined; however, they are hypothesized to be a result of divergent evolution.
Penises are one of the primary sexual traits, yet birds prove this theory wrong.
Anyone interested in reading the full article or watching an erect ostrich penis, go to the link below: