Living things have the ability to respond to their environment. That means both the internal environment and the external environment. For example, you as a living thing – your physiology and your behavior change if you get too hot or too cold. An ecosystem also responds to heat or cold. It is also a living thing, and it responds to its environment by changing the species of which it consists.
Organisms respond to change using the processes studied in embryology, physiology and behavior — the ecosystems and the Biosystem use evolution to respond to change.
Your physiology, and also your embryology and development, and behavior, are regulated by all the genes in your body interacting with your internal and external environment, so that you can take food and air and water, and use them to become what you are. In that way the genes, responding to your environment, produce you as a “thing,”
Put into my model of Life that I described in last week’s Bare Bones Biology blog, you can be thought of as a node produced by the network of processes that maintain your Life. The processes can be thought of as the invisible Life force, and you are the solid object that results. Solid objects (nodes, things) have phenotypes.
I’m sorry we must add another uncommon word to this story, but the word phenotype is important. Your phenotype is everything about you, from your red hair to your behaviors to your physiological responses to the environment. Mostly your phenotype is caused by the processes that are regulated by your genotype, and those processes are studied in the science of Genetics. Accidents (amputation for example) can influence your phenotype but not your genotype. Accidents are not inheritable. Your culture can be inherited, but only by your training, not by your genes.
Higher Life forms, such as an ecosystem or the Biosystem, also respond to change in the environment. Their responses to change are regulated by evolution, the natural Law of Life. Your body uses processes regulated by your genotype to grow and respond to change (and so be alive). The ecosystem uses all the phenotypes in the system – interacting with five other processes we discussed in order to grow and respond to change (and so be alive).
It was Darwin’s genius to recognize that living “things” (he was looking at organisms, but it could have been cells or ecosystems) all have slightly different phenotypes – color, behavior, health, any characteristic of a “thing” can be selected for or against, and so long as it can be inherited by the next generation it is a selectable phenotype that can respond to the power of the Law of Evolution.
In the Cosmos example, tameness was the phenotype selected for. This is the portion of evolution that Darwin recognized and we have come to think of as “survival of the fittest.” That term is nothing more than a silly reductionist sound bite, good for the human ego, but if we want to understand how evolution really does function and conceivably save ourselves by conforming to the Law of Life, survival of the fittest will be of no use to us. For one thing we are very far from the fittest species, because we would rather have money than survival. We will have to modify our own phenotypes (behaviors) so that we affirm and support the Life of the whole.
But that’s an aside, what we want to explain today is that natural selection or artificial selection act upon phenotypes, and most phenotypes are generated by genotypes. The genotype of each living thing is unique because of the way genetics works, which we are not discussing today. At all the various levels of organization of life from the most simple cell to the most complex Biosystem.
Genotype → Phenotype -→ Evolution
But remember that the processes of evolution can only use phenotypes that are inheritable from one generation to the next.
And we said all that so we could answer one of Gary’s original questions about epigenetics. Epigenetics is the study of heritable changes in gene activity that are not caused by changes in the DNA sequence.
Epigenetics is not relavent to evolution. Epigenetics is relevant to genetics, such as how genes are mixed around in cells, and how genes are regulated in cells to turn on and off. We have not been talking about genetics except to say that any trait or phenotype can be used in the process of evolution if it is inheritable.
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