First Organism |
In one of our puddles awash with the menagerie of Fred, Sofia, Roscoe, Sorrel, Nathaniel and Serena, we'd have a chemical soap opera that at some point would have created an interesting new character. Ménage à Six Once a big Nathaniel or several smaller Nathaniels happened to link together a Fred and a Roscoe, plus all three possible chains (Sofia, Sorrel and Serena), we would have our first self-replicating organism capable of assembling all of its own components from the local stock of raw materials. Let's call it a Caleb (short for Combined Almost-Living Elementary Blob).
A Caleb contains three aromatic chains:
It also contains three proteins:
Caleb Chemistry Within a Caleb, the Fred would read each of the aromatic chains, and produces a Fred, a Roscoe or a Nathaniel respectively. Elsewhere within the same Caleb, the Roscoe protein would hook up with each of the three chains, and replicate more copies of Sofia, Sorrel and Serena. Nathaniel would hold everything together so the transcriptions and replications could happen more efficiently. And the new Nathaniels would grab the various ingredients after they were created, and create new Calebs. Caleb can't directly replicate itself, but it can fill its local environment with all of the proteins (Fred, Roscoe and Nathaniel) and genetic chains (Sofia, Sorrel and Serena) that make up a Caleb. Once that happened, simple diffusion and covalent bonding could take over and assemble more Calebs. Of course when the Nathaniels linked things, they'd make plenty of incomplete copies that would be lacking one of the six components. But a few would happen to get some of everything, and be ready for official certification as another Caleb. Even half-Calebs would still have increased synthetic activity, and all it would take is a proselytizing Nathaniel to turn two half-Calebs into a whole. Caleb 2.0 The final step to a truly self-replicating organism would be a Caleb with specific binding sites that would only match with exactly one Fred and one Roscoe, and specific sites to carry one each of Sofia, Sorrel and Serena. That would be a Caleb ready to drift into any empty puddle in the world that had the right raw materials, and turn it into a Caleb-manufacturing machine. Second Explosion Any puddle with a Caleb and the right raw materials would produce more Calebs, and some of those new Calebs would leave home, and be carried by currents to distant locations. Of course, at this stage Caleb is still very dependent on a specific set of conditions. Just like the original Fred and Roscoe, it still needs just the right concentrations of two amino acid and two chain molecules to be able to reproduce, without too many foreign substances. But possibly an occasional wandering Caleb might actually splash into a utopian puddle on some distant shore, and set up its own local colony. Foreign Invasions Caleb did have one big advantage over Fred and Roscoe, when it came to adapting itself to new puddles. Each Caleb contained all of the ingredients necessary for self-replication, in one compact glob. Whenever a Caleb was lucky enough to drift into a hospitable puddle far from home, it was instantly ready to explode. The moment it arrived, Caleb would have created new copies of Fred, Roscoe, Nathaniel, Sofia, Sorrel and Serena from the local raw materials, which would then merge into numerous copies of itself. A Fred, a Sofia and a Sorrel could have done the same thing during the first explosion, but that would only happen if three different molecules all drifted into the same place at the same time. It would be a much less likely event than the appearance of a single Caleb. Alt-Calebs When Calebs reached almost-perfect puddles, they would have gone through the same sort of alt-ification process that we have already described for Fred and Sofia. They could have done that in small steps using slightly different molecules, or they could have evolved 'along the gradient'. It's pretty much the same alt-protein and alt-chain evolution that we talked about two chapters ago. Calebs could have also diffused into puddles that already contained alt-Freds and alt-Roscoes from the first explosion. There may have been a few of those about if there was a long gap between the arrival of Sorrel and the arrival of Caleb. Whenever that happened, all Caleb needed to do was to come up with an alt-Nathaniel and an alt-Serena that used the new raw materials, and it could have combined with the existing alt-Freds, alt-Roscoes, alt-Sofias and alt-Serenas to create a new alt-Caleb. Increased Evolutionary Speed Caleb was the first real organism, in the sense that there was a direct connection between its genotype, or genetic material (Sofia, Sorrel and Serena) and its phenotype, or body expression (Fred, Roscoe and Nathaniel). Any Caleb that contained a mutated form of Sofia, Sorrel or Serena that gave it a selective advantage, would have created more copies of itself than its cousins could have (at least when it splashed into a puddle of its own, with no other Calebs around). That means the potential for Darwinian evolution would have stepped up a notch from the previous, less-efficient puddle evolution. Of course, when a single puddle contained both a 'good' Caleb and a 'bad' Caleb, the 'good' Fred in the 'good' Caleb would still transcribe any bad chains that came its way, and the 'good' Roscoe would replicate any bad chains that it met. There wasn't the complete isolation found in modern cells. However, a 'good' Caleb would probably still have replicated more of itself, even when a 'bad' Caleb was in the same puddle, simply because its own 'good' chains were closer by. Caleb is still a long way from modern life, but it's a start. This is the first organism that can self-replicate, and the first to be able to attain at least some amount of Darwinian selection. Caleb had no competition, and nothing to fear except for too much UV, massive meteor impact, unfriendly proteolytic enzymes, and thermal decomposition in volcanic vents. As soon as a Caleb splashed into a new puddle that was just right, it would gradually consume all available raw materials, and turn them into more Calebs.
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