If aliens exist, do they have sex?

Though there's still no concrete proof of extraterrestrial life yet, evolutionary biologists already came up with a theory on how they could possibly reproduce.

Dr. Sarah Otto, director of the biodiversity research center at the University of British Columbia's Zoology department, said that the male and female genders is not a universal rule when it comes to species, and just like other creatures on Earth, aliens may be separated into different categories instead.

"The separate male and female sexes isn't even universal rule on this planet, let alone others," Otto said. "Rather than male and female, some species have categories like A, B, C, D and E."

Though it is possible for aliens in different categories to engage in sexual activity in groups, Otto said that only two genders among them participate in mating.

Otto added that it is also possible that the aliens are hermaphrodites, or creatures that possess enough male and female sex characteristics to enable them to breed on their own. Such traits have been observed on living things on Earth like slugs and other invertebrates, so the same could be possible with more advanced alien life forms.

"Organisms that can move and find other mates are more likely to have separate genders," Otto said. "Those that are stationary tend to have male and female organs on the same individual."

That doesn't mean that the aliens won't engage in sexual activity. All living creatures have a strong instinct to reproduce to continue their species. Therefore, it is not surprising that, through evolution, sexual activity becomes linked to the brain's pleasure centers.

It might be able to explain why some people report incidents of being sexually assaulted by extraterrestrial life forms.

Oddly enough, the difference in species apparently doesn't hinder aliens from engaging with the same behavior in humans. Many cases of aliens fraternizing with humans were reported during the 1960s, but were mostly ignored until the 1970s.

During this period, a man named Antonio Villas Boas claimed he was taken into a flying saucer and was forced to sleep with a female alien. Just this month, an American woman claimed that reptile-like alien creatures raped her at their base on the moon.