Random Character of Evolutionary Process

Random Character of Evolutionary Process

The smallest known free-living organisms are the PPLO (pleuropneumonia-like organisms) and similar small beasts. They are composed of about fifty million atoms. Such organisms, having to be more-self-reliant, are also more complicated than viroids and viruses. But the environment of the Earth today is not extremely favourable for simple forms of life. You have to work hard to make a living. You have to be careful about predators. In the early history of the Earth, however, when enormous amounts of organic molecules were being produced by sunlight in a hydrogen-rich atmosphere, very simple, non-parasitic organisms had a fighting chance.

The first living things may have been something like free-living viroids only a few hundred nucleotides long. Experimental work on making such creatures from scratch has already begun. There is still much to be understood about the origin of life, including the origin of the genetic code. But we have been performing such experiments for only some fifty years. Nature has had a four-billion-year head start. All in all, we have not done badly.

Nothing in such experiments is unique to the Earth. The initial gases, and the energy sources, are common throughout the Cosmos. Chemical reactions like those in a laboratory, may be responsible for the organic matter in interstellar space and the amino acids found in meteorites. Some similar chemistry must have occurred on a billion other worlds in the Milky Way Galaxy.

Molecules. The molecules of life fill the Cosmos, but I cannot tell you what an extraterrestrial being would look like. Image Purple Mosaic: © Megan Jorgensen (Elena)

But even if life on another planet has the same molecular chemistry as life here, there is no reason to expect it to resemble familiar organisms. Consider the enormous diversity of living things on Earth, all of which share the same planet and an identical molecular biology.

Those other beasts and vegetables are probably radically different from any organism we know here. There may be some convergent evolution because there may be only one best solution to a certain environmental problem – something like two eyes, for example, for binocular vision at optical frequencies. But in general the random character of the evolutionary process should create extraterrestrial creatures very different from any that we know.

We cannot tell what an extraterrestrial being would look like. We are terribly limited by the fact that we know only one kind of life, life on Earth. Some people – science fiction writers and artists, for instance – have speculated on what other beings might be like. But we must be sceptical about most of those extraterrestrial visions, because they seem to rely too much on forms of life we already know.