Genetic Variability and Evolution

We have already shown that evolution is a foundational reality of life on earth. We showed it in two ways. The first proof we gave is that we can do it. If humans can manipulate genetics to evolve new breeds of dogs, cats, cattle, horses, and other species, then of course evolution does exist. Even further than that, we can do genetic engineering. Not that we really want to discuss genetic engineering of plants and animals in this chapter, but I’m sure you have heard of it, and we can point to the fact that genetic engineering is possible only because we understand the basic principles of life that are required for evolution:

1. Genetics. The fact that genes are passed from parent to child;
2. The variability of phenotypes among all living creatures that is assured by sexual reproduction;
3. Selection of some genomes rather than other to pass on genes to the gene pool of the next generation.

The other evidence we have given for evolution is that life is defined by its ability to respond to external and internal change, and that the response involves inherited behaviors that preserve the life. This is true of cells that have chemical messengers and their receptors — and organisms that have brains and nerves and hormones — and it is true of ecosystems through the phenotypes of the organisms. A phenotype is a physical characteristic of an organism that is caused by a gene or genotype of that organism.

So now we want to describe how evolution functions in nature to preserve the lives of ecosystems. Next time, we will describe the basic processes that are required for evolution to happen.

First we’ll do a quick run through of genetic terms. We remember that each individual gene (usually) has one function that it regulates by making a specific and unique protein inside of some cell. Maybe this gene is responsible for your red hair, for a simple example. Mc1r is the name of the gene. Red hair is the name of your hair phenotype. Obviously, it takes more than Mc1r to make all of you, and in fact there are thousands of genes in each of your cells. Each pair of genes has a particular function that is associated with a particular phenotype. If you add them all together, the resulting phenome is YOU. All the genes that make up YOU are your genome. Your genome is not exactly the same as my genome. For one thing, your Mc1r gene codes for red hair and my MC1R gene codes for not-red hair. So we all have hair genes, but that does not mean we are all identical. Your genome is not identical to my genome.

A species is a group of animals of the same kind that could or do interbreed. So humans are all of the same species (Homo sapiens). Because humans can interbreed and often do, therefore we all share the same gene pool, whether we have red hair or not-red hair or kinky hair or unpigmented skin we all share the same gene pool. All the genes in all the humans is the gene pool of humans. The gene pool is even more variable than any of the genomes. This variability is the result of sexual reproduction (meiosis followed by fertilization) and is extremely important for survival of both the species and the ecosystem. It is the communication system of the ecosystem.

Different species do not interbreed (that’s the definition of a species) so they can not share the same gene pool. Every different species has its own function in the ecosystem. For example, most of the species of plants are producers, because they can make organic molecules using energy from the sun. Animals of different kinds are consumers. Consumers cannot make organic molecules (we have to eat them). One of our jobs is to help recycle the materials, carbon, oxygen, nitrogen, that the plants need to make more organic molecules. The energy can not be recycled, and that’s why the life of the entire ecosystem depends entirely on plants. And there are species that do all the other various jobs that are necessary to keep an ecosystem alive.

All the different species do their jobs in the ecosystem by their behaviors. So the ecosystem ocean of all the gene pools of all the different species is made up of a vast array of behaviors.

That’s the background.

Now I want to use an example to explain how this communication system functions. These are from two different species of flowers that I found in my front yard when I drove back home this afternoon.

Here is the first species. Maybe you can tell me what it is. All I know is that most of the plants have pink flowers, but this plant has white flowers. Let’s assume this species of plant has a job to do in the ecosystem, or it probably wouldn’t be here, even if we don’t know what the job is. We do know what flowers are for. The purpose of flowers is to do sexual reproduction so the plant can make more plants of the same kind. Sexual reproduction involves the fusion of sperms with eggs. Or in the case of flowers it involves finding some way for the pollen to get to the egg, and usually that involves some kind of insect, maybe a bee or some other kind of insect that is attracted to this flower. The genome of the insect determines its behavior. The genome of the flower determines its behavior. The two behaviors are both required for the flower to reproduce. In this case a mutation in one plant has caused the flowers to be white instead of pink. How might this affect the whole collection of organisms that do all the jobs in the ecosystem?

Are any of the regular pollinators attracted to white flowers?
Are the white flowers able to get pollinated?
Is some other pollinator possibly attracted to the white flowers?
Are the white flowers maybe MORE attractive to the normal insect or some other insect that normally doesn’t visit this particular kind of flower?
Do the white flowers for some reason survive better in our drought conditions of the past two years?
Which of these plants will make more babies for next year, the pink ones or the white ones?

Depending on the answers to those questions and many more questions during the development of the plant we will see next year either more or fewer of the white flowers. This is the process of evolution. This is life. This is the ecosystem being responsive to its environment by making available many different species that all have:

1- different behaviors
2- variability in the behaviors because there is variability in the gene pools of the species.

Without the ability to respond to internal and external changes, the ecosystem could not be alive.

The requirements for this responsiveness are two:

1- Phenotypic variability must be available, and this variability must be inheritable. We have already stated that most phenotypic variability is the result of genotypic variability. Genotypic variability is the result of sexual reproduction that we described previously. It is the norm in our ecosystem. If God invented sexual reproduction, it was not for your pleasure. It was to provide the variability that is necessary so the ecosystem can respond to environmental conditions.

2- In any species, on the averages, the individual organisms (and their genomes) that successfully raise babies are those that pass on their genes to the next generation. Natural selection is the process of choosing which genomes (out of the entire gene pool of the species) will be passed to the next generation. Natural selection consists of (on the averages) the combination of the phenotypes and conditions that both change with every breeding season. The genomes that can make offspring that survive best in the conditions of that particular growing season will be more likely to pass on to the next generation. The result of natural selection is that the some percentage of the gene pool is passed on to the next generation. In the next breeding season there will again be variability, because of sexual reproduction, and again only those organisms with the phenotypes that are most compatible with whatever the environment is that year — they will be the ones that breed and rear their young to make the next following generation. This is the process of natural selection.

Evolution is a change in the gene pool over time as a result of selection. Evolution is not a theory. It is a proven fact of life.

Evolution is NOT survival of the fittest.

Evolution is survival of the organism that helps the ecosystem to maintain its viable balance among all the thousands/millions of jobs that are done by the millions of species that make up the ecosystem and must be maintained in balance for the ecosystem to stay alive.

What remains, in our next blog, is to discuss are some of the methods the ecosystem uses to get rid of species that threaten this balance.

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