Half human, half alien offspring exist in many sci-fi and fantasy universes.  Mr. Spock from star trek, for example, had a Vulcan father and human mother.  Eldron from Lord of The Rings was said to be half-elven.  But what would be the actual likeliness of a human being able to breed with another humanoid of seemingly different origin?  We know biology has mechanisms that prevent this on our own planet.  Dogs can’t breed with cats.  Sheep can’t breed with horses.  Even humans can’t breed with our closest biological relatives, monkeys, though I’m not sure if anyone has actually tried. Human-alien breeding might not be possible. Today we look at why.

Definition of a Species.

There are many factors scientists consider when researching new species and hybrids.  A species, as defined by the biological species concept, are groups of organisms that can potentially breed and produce offspring that are fertile.  A hybrid is a product of two similar species breeding to produce offspring that is not fertile.  A horse and a donkey can breed to produce a mule.  However, mules are infertile and cannot reproduce.  Therefore, a mule is a hybrid.  All of that being said, characters like Mr. Spock and Eldron are not technically hybrids even though they are sometimes referred to as such.  They are new species since they are able to have kids of their own.  But there are many barriers that prevent this kind of thing for most species.

Likely Barriers to Human-Alien Breeding.

Ignoring the fact that we have never met an alien, a likely barrier to human-alien breeding, could be mechanical incompatibility.  This is where the physical form of a being and its sex organs make it impossible to breed with something else.  Most mammals on earth have very similar sex organs; the males have a penis and the females have a vagina.  But this may not be the case for an alien species.  A good example of this can be seen in the movie Avatar.  The Na’vi have been described by James Cameron as having no actual sex organs, other than the females have breasts.  Since their breeding is done by connecting that weird hair tail thing with each other, and since humans don’t have a weird hair tail thing, breeding with them would be impossible without scientific intervention.

Gametics

The biggest barrier to human-alien breeding would most likely be Gametic Incompatibility.  Gametic refers to reproductive cells, such as eggs and sperm.  Gametic incompatibility is where a sperm and an egg (gametes) are unable to combine to create a viable cell.  Sometimes, this can be caused by sperm being unable, or not well suited to navigate its way to the egg.  Most of the time however, it has to do with the proteins that egg and sperm cells are encased in.  these proteins allow the gametes to recognize each other and act like a key, allowing the sperm to penetrate the cell wall of the egg.  Without the proper protein combination, fertilization is impossible.

Lack of interest

There is the possibility that when aliens show up, we have no interest in breeding with them.  This of course goes both ways, maybe they wouldn’t want to breed with us.  With all the different ways humans have described or visualized aliens, I can think of several dozen that nobody would want to make offspring with.  Furthermore, maybe the aliens have different methods or mechanisms for making babies.  That is to say, maybe they aren’t mammals. If aliens were closer relatives to lizards or insects, I doubt there would be much interest in hybridization.  If the genetic similarities are too far apart, making a hybrid would be exceedingly difficult. There is also the possibility that we are sexually compatible, but the aliens just don’t like us. To read more about how to get aliens to like you better, click here.

Speculation.

if the aliens are similar enough to us, these barriers could likely be overcome through scientific measures.  However, since we don’t have any aliens around to study, it would be hard to tell how likely that would be.  Just because life on earth is carbon based and all contains DNA doesn’t necessarily mean ALL life in the universe would be that way.  Many sci-fi series have talked about silicon-based life which would probably not be very compatible with our carbon-based bodies.  Other factors would have to be considered before even attempting to make a new species, such as environmental conditions.  An alien from a frozen planet with a methane-based atmosphere would probably not be very compatible with human life, even with massive amounts of genetic engineering.

While there are a lot of factors that could hinder the possibility of human-alien breeding, until we meet a being not of this earth, we can only speculate.  Maybe the aliens would look similar to us, and have similar parts.  Or maybe they would be jelly fish flying around space in huge fish tanks.  There is a theory called Panspermia that suggests that all life throughout the universe would be similar, because it all came from space.  If this turns out to be true, the potential for hybridization through natural or scientific means becomes much more likely.  Let us know what your thoughts are by dropping a comment below.