Monday, October 19, 2015

Chain Reactions, Life Origination, Mutations, and Memes

Chain reactions in nuclear reactors are the means by which power is released from the uranium nuclei. One neutron strikes a U-235 nucleus, and it fissions, releasing two or three neutrons. This second generation of neutrons goes on its way, and one or more of them possibly strikes another U-235 nucleus, and the same fissioning occurs. At each generation, two or three neutrons are produced when one is absorbed. There are losses, but if the number of neutrons effectively striking a U-235 nucleus is larger than the number that do in the previous generation, there is increasing power generated. If the number of neutrons is the same for each generation, there is stable power generated.

In a large block of reactor core material, there can be great differences in the ratio of neutrons of succeeding generations. If there is one region which can be isolated which has a ratio of one or more, a persisting chain reaction continues. What happens in other regions influences the ratio, as if in neighboring regions, only some ratio below unity is maintained, the neutrons produced each generation can slip back into the most productive region to help maintain the reaction there. But if there is no region where the ratio is above one, there is no chain reaction.

The mathematics of neutron multiplication in nuclear reactors is simple to understand, but it is not isolated to this single example. Consider instead the origination of life. One hypothesis, discussed in another post, is that there is a molecule, probably some amino acid combination, which can replicate itself if the right amino acids contact it. There are certainly processes which will disassemble the amino acid combination. If an average replicating combination can make more than one copy of itself before it disassembles, we have a chain reaction, and the number will increase. The observation that was noted with respect to neutrons and fissions is also true for amino acid combinations and replication: if there is a region where the ratio is higher than one, replication will succeed and numbers will increase. Other regions may have lower ratios, and contribute to what happens in the most successful region. But if there is no single region where the ratio exceeds unity, replication cannot succeed and life origination does not accomplish the critical first step.

There are multiple conditions which affect the multiplication rate for neutrons and fission and also for the replication rate of amino acid combinations. Conditions change in a nuclear reactor core as more U-235 nuclei disappear through fission, and other elements present absorb neutons and transmute. Adjustments or some feedback mechanism is needed to maintain power production for an extended period. The same happens with the replication of amino acid combinations. The conditions have to be maintained for a long time, in fact, for long enough that some modification can be found by random chance that has a higher replication rate or is more tolerant of variations in conditions; likely the modification is more complex. Life originates if through the many, many steps needed to form cells and then to allow them to become more diverse with specialization and other features, the right conditions for each of the steps is maintained for a long time, long on the evolutionary scale.

This means that the same situation exists for successive mutations as exists for the original replication that occurred at the very start of the origin of life. Each mutation produces something that can self-replicate, provided the conditions are right, in a generational ratio greater than one. By the time a mutation is established, the conditions necessary for previous steps can change, so that the previous step cannot be repeated. Life goes onward, not backward. There again must be some region with the right conditions for extended time. The region can be different for different steps, and undoubtedly will be for steps sufficiently distant on the chain of evolutionary organisms. Some examples are more than obvious: amino acid combinations need to replicate in a soup containing amino acids of the right variety; cells replicate in situations where whatever food they require is present; photosynthetic cells need sufficient photons of the correct wavelengths; and so on.

There is a profoundly important implication here. Mutations are local, not global, and might be restricted in geographic extent. What evolves in one place is not what evolves in another place. This is obvious with respect to flora and fauna, but it is just as true with something invisible: individual genes controlling individual characteristics, or contributing to them. Genetic improvements occur locally, and may or may not disperse globally. This means that an alien planet may have very diverse populations in the period prior to civilization starting, when trade and migration become common.

Memes are often analogized with genes, but the basic mathematics is what is the same. In order for a meme to persist in an alien civilization, there has to be a locale where the number of young learning the meme and learning to transmit it are equal to or greater than one. Memes can die out just as easily as genetic mutations. The conditions in the locale where they are present can change, and replication can be less than one, meaning the meme will disappear in time, after a long period where there were some followers, but less and less each generation.

Another thing that should be noted is that neutron multiplication, life origination, mutation persistence, and meme propagation can have growth rates higher than one, and if the conditions are right over an extended geographic area, can spread like a prairie fire. There is a natural speed by which each of them can propagate, which is dependent on the rate of transmission of a carrier, such as a neutron of the right speed. The first instance of the mutation might find that the characteristic that is engendered by the mutation increase the replication rate per generation by a significant amount, and this occurs in a wide area as the conditions it can tolerate are larger than previous mutations. Away runs the mutation, or the fission, or the meme.

This has implications for seeding by alien civilizations. If they can find the right mutation, one that diverts the normal evolution that is occurring on a colony planet to a direction they prefer, and it can have a higher replication rate than the native cells, or organisms, it could spread quickly and transform the planet’s biological structure. This blog has not yet examined the mechanisms by which seeding could be done, but it obviously is a most interesting topic.

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