Friday, August 5, 2016

Best is Not So Good in Evolution

Evolution is perhaps the most detailed step on the process of bringing alien civilizations into existence. It consists of millions of simple steps, ruled by a selection process, that eventually produces organisms that meet some fitness criteria, which changes with time. Most simple steps are fatal, most of the rest of degrading of fitness, most of the remaining ones are indifferent to fitness, and a few are improvements. But they are tied together.

Consider the genetic machinery inside the cell itself. There are three pieces, according to one simple way of categorizing them. They are the ones which support life in the cell, meaning ones which take in foodstuffs and modify them, extracting energy or repair materials and removing waste chemicals. There are ones which build the cell, including the process of making a copy of every part and moving them so that reproduction can take place. These involve reading the genetic code and doing what it says, mainly building various proteins and a few other organic molecules. Then there are ones which reproduce the genetic code itself, so that a reproduction of the cell can have a genetic code copy for itself.

For the first category, there are, in most cases, multiple copies inside the cell, so that damaged parts can be ignored or repaired without much influence on the survival and reproduction chances of the cell. In the second category, errors in reproduction might be swamped by the numbers of things which are produced. For this second category, there might be layers of cellular machinery. One layer might work with the genetic code itself, making the second layer of machinery. The second layer might make a third layer, or actually produce things in the cell itself. Errors in the second or later layers are more likely to be inconsequential. If the genetic code is only read once, then that reading could have a fatal or otherwise serious effect on the cell, but if the genetic code is read over and over to make more copies of the same stuff, redundancy saves the day.

What actually does the reproduction in a cell? Consider the cell wall, which might be simple or very complex, depending on which stage of evolution you are considering or which cell at a particular stage. Either way, there is internal, second or later layers of cellular machinery which repair the existing cell wall, and likely build more as needed. When something signals a time to reproduce, this same machinery can start expanding the cell wall, increasing its area, which can be used for both the original cell and the copy cell. Here again, errors don’t matter much if the layer-generating machinery is sufficiently redundant. With cell molecules numbering upwards of millions, there should be significant redundancy in the machinery which produces them.

Thus, cellular reproduction, as envisioned by this example, doesn’t take place with the genetic code making much new proteins, but instead, the production machinery is already there, and some signaling is what is needed. A previous layer, one that makes the primary production cellular machinery, might have to make more of it. Thus, the genetic code doesn’t seem to be much needed in the reproduction of a cell. Does it produce the signaling that is used to build a dividing wall, or does it somehow keep track that all necessary parts have been produced and neatly divided so the dual dividing wall can be constructed? Or has it generated a set of timing proteins which do the measuring and signaling? Perhaps that is the only set of molecules that has to be produced directly by the genetic code in the original cell. If not, there is not likely to be a large number of things that have to be produced in this reproduction process. It certainly does something connected to reproduction, else cells without a genetic nucleus could survive and reproduce on their own.

If it is not the whole genetic code that is involved in reproduction or maintenance, once the first layer of cellular machinery is in place, this means reproduction can take place with significant errors in the genetic code caused by mutation, and they will not manifest their effects until later on, when some primary cellular machinery has to be produced, and changes happen.

The third part of the genetic code reproduction consists of copying the code itself so that each one of the resultant cells can have its own copy. This copying process has its own mechanisms, and can make its own errors. Suppose there was redundancy or some other forms of error-checking and correcting, and for the purposes of illustration, consider a cell which had developed this to a high degree. It does not make genetic code errors. This means that there is no fatalities caused by this source. A reduction in fatalities means a higher fitness, so this should survive and out-compete cells identical except for this error-correction scheme. So, why isn’t this present in Earth cells?

Because there is something which might be called meta-competition. Cells which mutate at some small rate lose in the fitness competition, but when one of the mutations scores big and wins the fitness competition by a significant amount, that benefit outweighs the benefit of having error-correction working strongly. It’s a gamble that cells win by playing the mutation lottery. Lots of small losses occur when there is no benefit or some degradation to fitness occurs, but one big win erases them. If the mutation rate is too high, the losses mount up too high and the cell with a high mutation rate loses, but if it is too low, too few chances exist for the next stage of evolution to happen.

This means that there is some optimal mutation rate, which might depend on circumstances such as the survival to reproduction probability of cells. The same thing should happen, not just in single celled organisms, but in anything which exists and might compete in the mutation lottery.

This process should be the same on all planets which experience evolution. It is just one more example of interstellar convergence.

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