Much as I love the idea (and the show), the likelihood of a human being able to engage in any hot bow-chicka-bow-wow with an alien, and have that union produce an offspring, is damn near zero. Even if the two in question had all the various protrusions and indentations more or less lined up, the main issue is the compatibility of the genetic material. I mean, consider it; it's usually impossible for two ordinary terrestrial species to hybridize -- even related ones (say, a Red-tailed Hawk and a Peregrine Falcon) are far enough apart genetically that any chance mating would produce an unviable embryo.
Now consider how likely it is to have genetic compatibility between a terrestrial species and one from the fourth planet orbiting Alpha Centauri.
Any hope you might have had for a steamy tryst with an alien was smashed even further by a study that came out of a study from the Tokyo Institute of Technology, Emory University, and the German Aerospace Center. Entitled, "One Among Millions: The Chemical Space of Nucleic Acid-Like Molecules," by Henderson James Cleaves II, Christopher Butch, Pieter Buys Burger, Jay Goodwin, and Markus Meringer, the study shows that the DNA and RNA that underlies the genetics of all life on Earth is only one of millions of possible information-encoding molecules that could be out there in the universe.
It was amazing how diverse these molecules were, even given some pretty rigid parameters. Restricting the selection to linear polymers (so the building blocks have to have attachment points that allow for the formation of chains), and three constituent atoms -- carbon, hydrogen, and oxygen, like our own carbohydrates -- the researchers found 706,568 possible combinations (counting configurations and their mirror images, pairs of molecules that are called stereoisomers). Adding nitrogen (so, hooking in chemicals like proteins and the DNA and RNA nitrogenous bases, the letters of the DNA and RNA alphabets) complicated matters some -- but they still got 454,442 possible configurations.
The results were a surprise even to the researchers. "There are two kinds of nucleic acids in biology, and maybe twenty or thirty effective nucleic acid-binding nucleic acid analogs," said Henderson James Cleaves, who led the study, in an interview in SciTechDaily. "We wanted to know if there is one more to be found... The answer is, there seem to be many, many more than was expected."
Co-author Pieter Burger of Emory University is excited about the possible medical applications of this study. "It is absolutely fascinating to think that by using modern computational techniques we might stumble upon new drugs when searching for alternative molecules to DNA and RNA that can store hereditary information," Burger said. "It is cross-disciplinary studies such as this that make science challenging and fun yet impactful."
While I certainly can appreciate the implications of this research from an Earth-based standpoint, I was immediately struck by its application to the search for extraterrestrial life. As I mentioned earlier, it was already nearly impossible that humans and aliens would have cross-compatible DNA, but now it appears that alien life might well not be constrained to a DNA-based genetic code at all. I always thought that DNA, or something very close to it, would be found in any life form we run across, whether on this planet or another; but the Cleaves et al. study suggests that there are a million or more other ways that organisms might spell out their genetic code.
So this drastically increases the likelihood of life on other planets. The tighter the parameters for life, the less likely it is -- so the discovery of a vast diversity of biochemistry opens up the field in a manner that is breathtaking.
... but the chance that the aliens will look like this is, sadly, pretty low.
This raises the problem of whether we'll recognize alien life when we see it. The typical things you look for if you're trying to figure out if something's alive -- such as a metabolism involving the familiar organic compounds all our cells contain -- might cause us to overlook something that is alive but is being carried along by a completely different chemistry.
And what an organism with that completely different chemistry might look like -- how it would move, eat, sense its environment, reproduce, and think -- well, there'd be an embarrassment of riches. The possibilities are far beyond even the Star Trek universe, with their fanciful aliens that look basically human but with odd facial structures and funny accents.
The whole thing boggles the mind. And it further reinforces a conclusion I've held for a very long time; I suspect that we'll find life out there pretty much everywhere we look, and even on some planets we'd have thought completely inhospitable. The "Goldilocks Zone" -- the region surrounding a star where orbiting planets would have conditions that are "just right" for life to form -- is looking like it might be a vaster territory than we'd ever dreamed.