OrionWorks - Steven Vincent Johnson wrote:
> Statistically, in terms of how we understood evolution to work, to have > encountered such a large amount of genetic uniformity made no sense to > us. We assumed evolution would have naturally engineered more diversity. . . . > ... The atmosphere was > subsequently reseeded with a new strain of bacteria, a strain possessing > a hauntingly similar singular genetic source. Entertaining story, but I have a minor nit to pick with the ending. Bacteria are prokaryotes, while us big folk are all eukaryotes. That difference illustrates the enormous evolutionary gulf between bacteria and us. The point is, one bacterial genome seeded on a planet would be totally lost in the evolutionary noise when you fast forward a few hundred million years (and several trillion bacterial generations) to get to the first intelligent life form. While the frequent occurrence of DNA based life would be surprising in itself, this scenario really wouldn't lead to us seeing remarkably similar evolved forms or genomes, and in fact the genomes we'd see in other star systems would surely be completely unrecognizable, with no apparent similarities to our own. In short, this scenario would not lead to a "large amount of genetic uniformity"; indeed, given the number of steps from the first bacterium to, say, an insect, it's not even clear it would lead to the same set of codons being used everywhere. To draw an analogy, it would be like comparing Chinese Han characters with Cyrillic. They're both alphabets, but showing they have a common ancestor would be nontrivial, and actually projecting back to that common ancestor would be just about impossible. Their "evolution" has apparently not been at all similar, despite having "grown up" just a few thousand miles apart.
