Asked in Microbiology

In evolution theory why is random mutation random while natural selection is not random?



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Natural selection works on a simple premise that the better equipped have more chance of survival and reproduction. The fact that the 'better' animal has more chance of producing offspring means more of his or her genes reach the next generation than his or her weaker rivals, thus weakness is filtered out. Although luck and chance can come into the equation (a 'weaker' animal may get lucky) in the long run over generations and generations, luck is no match for 'good' genes which enable advantages in the fight for survival. The chemical process of reproduction is slightly different. When cells are creating copies of themselves to make the new being, they are essentially copying enormous sets of instructions that their parents cells followed to create them, and the offsprings cells will use to build them. As the instructions are so huge, the number of cells involved is so colossal, the number of animals involved in reproducing is vast, and the number of generations and generations, and millions and millions of years… the opportunity for 'mistakes' is likewise gigantic, no matter how accurate and efficient the cells involved are supposed to be. These 'chance' mistakes are actually something like 1 in a giga-mega-godzillion (not an official statistical measure I might add!) but because the process happens more than a giga-mega-godzillion times, mutations are seen to occur. These mutations can either improve the animal slightly, or hinder it. The mutations are never that huge as the new being would be unable to survive or find a mate if it drastically differed from the species as a whole. Of course, any improved instructions which give the being a slight advantage, have more chances of being copied in the future - the mutation is now the new standard. An interesting position on this is that cells actually evolved with this chance of mutation. Cells which were 100% accurate in their reproductive instruction copying never hit upon anything new, or advantageous to the species while the world changed around them. What was a good design then, perhaps isn't so good in today's world. Meanwhile, cells which had a 99.999999…..% accuracy were actually more successful in the fight for survival as they enabled the opportunity for mutation, and thus the opportunity for improvement - a species which can change with time is far more likely to survive in a world that too changes with time. With this in mind, you could argue randomness in cell mutation was actually naturally selected by a non-random process!