Xenobiology: No, Seriously, It's Not The Same

So I was watching Through the Wormhole with Morgan Freeman last night, and they were talking about like alien life and all that fun jazz, something about "shadow biosphere" consisting of local flora and fauna with fundamental genetic differences, creating life in the lab, etc etc.

In all these discussions, though, these folk seem to continue to make ridiculously huge assumptions. Like the idea that because we're based on four particular nucleotides (five, really, but that's not the point yet), that all life is going to be based on those nucleotides.

...lolwut?

Amino acids are almost assuredly wide and varied in number; the possible combinations that could be used in genetics is probably ridiculously staggering. Not only that! - but we can clearly see that there are alternatives to our standard nucleotides, since freaking RNA uses a replacement for thymine (namely uracil). Why the hell would we assume that alien genetics would see the same freaking materials we use?

And our assumptions get worse! We assume all kinds of crazy things about DNA to be held true across all instances of life. Double-helix, four nucleotides, with sugar/phosphate stuff providing the ladder. But hey, chemically, elements in the same family (or column or whatever the hell) tend to have similar properties. Bonding issues with electron shells and whatnot aside, you could probably reasonably replace the phosphorous in DNA with, say, arsenic! Or antimony! Or bismuth! Or freaking nitrogen!

Put these two concepts together. Envision, if you can, alien genetic structures that have six nucleotides with sugar/antimony ladders for their "DNA." Increased numbers of nucleotides give rise to increased possible combinations, leading to greater potential genetic diversity. I don't know what the antimony instead of phosphate does, but I'm sure it has some effect (I'm not a geneticist, for serious, nor a chemist).

But the important thing is the idea that the number of nucleotides could be different, and even the specific nucleotides could vary. Our genetic language has ACGT and sometimes U; for an alien species, they could be doing CDIGHL and sometimes RT (just making up letters, here).

Even more important than the specifics of alien genetics is the idea that xenobiology has the potentially to be pants-crappingly more complicated than modern science seems willing to admit or discuss. We have to use life on earth as a starting point, because that's all we have, but when it comes down to it, there is no way to tell just how freaking different life elsewhere can or will be.

Even the idea that alien life will use a DNA-analogue seems presumptuous. Our understanding of life is such that amino acids and such seem to be a necessary component, but we have no basis for that assumption other than that amino acids are a sufficient but unnecessary component. The real winner is finding the necessary but insufficient component, the piece that is the same across all life, regardless of the components it is made from. I don't think we can do that yet, given our limited access to life as it exists in the universe, but that's what we need to be looking for.

...okay, so after a short look on Wikipedia, apparently there is a divison between astrobiology and xenobiology, namely that astrobiology is looking for earth-like life elsewhere, while xenobiology is the reasonable one that is all "no, seriously guys, it could be anything." But still, that just means that astrobiologists are silly. Looking for earth-like life - and finding it - would be cool, but the chances of that happening seem... pretty small, to me.