Interesting subject. Hermaphrodites are generally held to hail from Europa, a cold, icy moon of the planet Jupiter, the resulting low temperatures being the cause of their indeterminate gender.
Unsurprisingly, both the Martian and Venusian populations seemed doomed to extinction until they established a hysperspace link across the solar system, enabling free travel between the two worlds and the consequent breeding of the genders. The results of this genetic union then travelled to Earth, setting themselves up as the next evolutionary link after the apes. We are the Venusian-Martians! Oh yes, it's all there in von Daniken's theories if you look closely enough.