Once upon a time on a flat planet was living two peoples : one on a side and the other on the other side. One side was always in the dark and the other always under the light. The two people have never met and didn’t even know the existence of each other. The dark ones was short, without any hairs on their corpse, did not have any eyes and had sonar instead. They stood on their two posterior feet like all ape-descendant species living on their side. The light ones was tall, with an profusely hairy corpse, had very big eyes in a vertical shape with two eyelids : a light filtering one and a completely opaque one. They stood on their two anterior feet like all reverse ape-descendant species living on their side.
The dark side was looking for heat and the light side for cold by digging their soil. Each people noted that the more they dug, the more they got satisfaction in regard to their primary goal. And guess what, the started to dig deeper and deeper over time.
And one day, one side finally reach the other side. One of the dark side pierce deep enough to reach the light side. He felt for the first time of his life the heat’s light. And almost at the same time, one of the light side pierce also enough to reach to dark side. He viewed also for the first time in his life a completely dark world. The two side started to celebrate the other side discovery and to explore their opposite side. The light ones tried to bring the light with them in order to be able to see where they wanted to go. The dark ones were slowed down because of the heat. So far, no one side people met other side people because the two holes ended in uninhabited places. But the two species encounter was only a question of time. And that time finished to happen. And at that time started a war between to two species. The first encounter was a shock for the two species that started to feel an irrepressible fear : who were they? what are they? when did they arrive? The fear finally won over more reasonable approaches and the darks against lights war started. After years of war, since the two species are diametrically opposed, none take advantage over the other : statu quo with a bunch of deads. One remarkable thing was that the two species were genetically compatible even if they didn’t notice it since their encounter. And the inevitable happened, a male sexual organ of one specie finally met a female sexual organ of the other. And the birth of a new species happened : the baby had eyes and a sonar, was hairy only on relevant spot to protect against the light and could stand on their anterior or posterior feet. The best of the two worlds. It was the beginning of a new era where peace and sexual exchange between the two species should be omnipresent and the rise of a new specie suited for both worlds would start to populate the two sides.
So in the end, it’s better to fuck than start a war with unknown species.