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Making Aliens: Part 2

30 Oct

Last time in this thought experiment I posited that, if I had to create the most probable aliens, I’d start with some basic chemistry. Namely, aliens cells would likely be based on large carbohydrate structures that separated pockets of liquid water solutions, mostly due to the great abundance of these building blocks.

Plus, it’s been shown that most of these basic molecules will form on their own. The famous Miller-Yuri experiment created many basic molecules, hydrocarbons, and even amino acids, out of nothing more than simple gases and energy. Amino acids are another of the great ingredients of life – chained together amino acids form the proteins and enzymes that power our cellular machinery. In fact, it’s so easy to make them that amino acids have even been found inside meteorites and in interstellar dust clouds. So, given their abundance and usefulness, I think I can finish our chemistry section by saying that alien cells will use amino acid-based proteins.

From here I’ll jump up a level and think about:

Part II: The Evolution of Aliens

So we have some basic water-carbohydrate-protein cells. They’re able to organize themselves thanks to their cell walls and maintain that organization thanks to cellular machinery and some basic genetics. The more sophisticated mechanisms will also allow them to respond to environmental changes like heat and pressure and obtain energy. Energy basically comes in two accessible forms, either radiation or chemical bonds, so our alien cells will either be photosynthetic, chemosynthetic (like deep-sea bacteria), or eat other life for their tasty nutrients (like we do).

So, we have some cells. But there’s one last thing they need to do before we can really consider them alive. And that’s reproduce. Without some form of reproduction and evolution, the cells will stay as they are, primitive conglomerations of chemicals, likely to die out at the first unfavorable shift in the environment. So it’s unlikely that we’ll ever find alien cells incapable of evolving.

Now, similar to the definition of life, there are some basic things needed for evolution. They are:

  • Information
  • Consequences
  • Heritability
  • Mutation

The information will be our cell’s genes. The structures and plans encoded within will, ultimately, determine the cells fitness, ability to survive and breed. Good genes lead to high fitness, bad genes lead to poor fitness. These are the consequences. High-fitness individuals will pass this information to their descendants, forming a chain of heritability. Finally, in order for new genes and new plans to develop, there needs to be mutation. Somehow the genes need to change, either through damage (such as from high-energy radiation), invasion (such as from viruses), or sloppy reproduction. A population whose genes never change is not actually evolving.

Now, it’s possible that we’ll never progress beyond this stage. Future explorers on some distant planet may find life in the form of a homogeneous soup of free-floating cells. However, this doesn’t mean that they wouldn’t be evolving. On Earth there is a strange phenomenon among the unicellular world where a cell’s genes aren’t one-hundred percent tied to that specific individual. Cells pass genes like trading cards, a process known as horizontal gene transfer. In these communities it’s quite difficult to distinguish between species of cells, to the point where some scientists have argued that it would be better to consider them to be one super-community instead.

Aliens that achieved this would probably look like some sort of bacterial muck. Really cool from a scientific standpoint, but not terribly interesting.

Might stain your boots, too.

But let’s say this doesn’t happen. Although this is probably what life on Earth looked like in the very beginning, it didn’t stay that way and there’s no reason to believe it would to our hypothetical aliens. What’s more likely is that, eventually, barriers will appear within this population and a process known as speciation will occur. Sometimes these barriers will be physical, like a mountain range, other times they’ll be behavioral or physiological. Perhaps, if the cells exchange genes, some mutation will occur that blocks this process. Perhaps cellular cliques will appear. Either way, for some reason or another different non-mixing communities of cells will appear and, over the course of time, they’ll differentiate into a vast array of species.

From here evolution will be in charge. Natural selection, genetic drift, and random events will keep the populations evolving and changing. Next time I’ll expand my scope outwards and consider multicellular life, evolutionary strategies, and, perhaps, even discuss how intelligence might arise.

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Posted by on October 30, 2012 in Natural History

 

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