system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the skin on penises so dark, compared to other parts of the body, like torso and such.

I've always wondered this, how is this possible? Not like it gets much sunlight.

Sorry if wording is wrong, English is not first language.
gpt
Dermatologist here. There is more melanin in genital skin, in both men and women. Genital pigmentation increases in response to sex hormones. 
For example, newborn babies have particularly dark genital skin due to the influence of maternal hormones. This pigment gradually fades after birth before returning at puberty due to rising hormones in adolescence.