01.20.06
Non-random Mutation
Molecular biologists don’t generally let on about all they know, suspect, or don’t wish to tell the public.
Lynn Helena Caporale lets the cat out of the bag in
Darwin in the Genome, Molecular Strategies in Biological Evolution (McGraw-Hill, 2003)
The work described in this book has led me to the conclusion that natural selection must work not just on each individual mutation, but also on the very mechanisms that generate genetic variation-as it does on all biological functions. The research discussed in this book leads to the conclusion that mutations are not all accidents and that mutations are not always random. Our genomes, and those of other life forms, have evolved mechanisms that create different kinds of mutations in their DNA, and they reuse and adapt useful pieces of DNA, even to the point that there are genomic “interchangeable parts.” Biochemical mechanisms can arise that tend to focus genetic variation, resulting in “hot spots” of genetic change at certain places in the genome. The probability of genetic change at any given point in the genome is dependent upon the surrounding sequence of the DNA, the environment, and the proteins that are present in the cell that interact with the DNA; for example, specific types of mutation can be increased in our immune system.
Evolution may not have been reaching for the goal of two eyes and a brain and two arms and two legs, but it didn’t just stumble onto us through clumsy wandering. Randomness fades in a world that rewards each step of getting better at finding food, avoiding predators, or adapting to recurring challenges. As the dust organized, it faced selection. Over time, there emerged something that, viewing the effects now, we might call strategies- such as the ability to actively generate diversity-that enabled life to emerge from the darkness of random wandering. Because the mechanisms that change the genome fall under selective pressure, I propose, based on the new observations discussed in this book, that information can flow back from survival to the places in the genome that affect the generation of the diversity that we see around us, and that this will make.genomes become more efficient at adapting and evolving. If one of the predictable characteristics of the world is that it changes over the course of generations, natural selection will lead to organisms that are more efficient at adapting to an environment that may change.
These discoveries do not refute the theory of natural selection developed by Darwin and Wallace, but instead provide a deeper understanding of how natural selection leads to organisms that are better adapted to their world. Natural selection acts on all biological properties. That means that natural selection acts not only on fins and wings, but also on the mechanisms that change a genome. With time, it turns out, the “fittest” genomes, the “successful” genomes-the ones that survive–are the genomes that evolve what here I will call mutation strategies. Some readers may disagree. with this use of the word strategies, as I am, after all, discussing groups of molecules. But I use this word to emphasize that the molecular mechanisms I will describe in this book have the effect of anticipating and responding to challenges and opportunities that continue to emerge in the environment.
The first strategy for survival clearly is to generate diversity. The long- term survival, or fitness, of a genome often depends upon the diversity of its descendants. Genomes have evolved biochemical mechanisms that actively diversify themselves. The more diverse the progeny, the better the chance that at least some progeny will be different in a way that allows them to survive or even thrive, whether they are in an isolated canyon, a salt cave, a hot spring in Yellowstone National Park, or an irradiated can of meat-for life can survive in all of these places.