3: The Selfish Gene
The Selfish Gene Theory was discovered by Richard Dawkins. Prior to 1976 biologists knew that biology was made up of chemical reactions, but it was made up of so many chemical reactions that no one person could keep track of them all.
The Selfish Gene Theory is a perspective that unifies the chemical reactions of biology by identifying the end result of every chemical reaction. Every chemical reaction in biology contributes, in one way or another, to the replication of the genes that started that chemical reaction. Dr. Dawkins explained this in his book The Selfish Gene, and built upon it in his books The Blind Watchmaker, Climbing Mount Improbable, and The Extended Phenotype.
A gene is a molecule that makes copies of itself when it comes into contact with the right combination of other molecules. In humans, the genes are stuck together into 23 pairs of chromosomes. The 23 chromosomes in a sperm cell have to get paired up with the 23 chromosomes in an egg cell to start the chemical reaction. Then they react with the other chemicals that are present in the egg cell. Then more chemicals get added through the woman’s uterus, and then more chemicals get added from the milk and food and water the infant consumes, and so on for 18 years and 9 months, until that gigantic chemical reaction turns a fertilized egg cell into an adult human.
As an adult you’re sexually mature, so you can have children of your own and then feed them and otherwise raise them, and do all the things you need to do to keep yourself alive in the meantime, and then help raise your grandchildren, and keep making more copies of your genes. If you’re lucky, your chemical reaction runs down after 80 years or thereabouts and you die of old age. If you’re not lucky, something disrupts your chemical reaction prematurely and you die of some other cause. The lifecycle of every animal, plant, fungus, virus, and bacteria is a variation on this basic process.
The Earth formed about 4 1/2 billion years ago, and life began on Earth about 3 1/2 billion years ago. After a billion years of molecules floating around all over the Earth and getting hit with energy from sunlight, volcanic eruptions, lighting, and radiation, some carbon atoms hooked up with some other atoms and formed a molecule that started a chemical reaction that made a replica of itself. And there’s a lot of carbon in the world, so those two molecules then started two more chemical reactions, and then there were four molecules. And then eight, and so on.
With all those chemical reactions making things change, variation began. Some of those chemical reactions would’ve happened under conditions that weren’t ideal, but were close enough to make something close to the chemical reaction happen. The Earth is also constantly being bombarded by cosmic radiation, which added more variation to the chemical reactions. Some of those chemical reactions didn’t produce perfect replicas of the original molecules, but molecules that were slightly different. But those new molecules could still make replicas of themselves. So they made replicas of themselves. They didn’t make replicas of the original molecules. So now there was more than one kind of self-replicating molecule in the world.
Now, after 3 1/2 billion years of that chemical reaction taking place all over the world, the chemical reactions that are the most stable are the ones that keep happening. Each part of that chemical reaction is happening among all the other chemical reactions, so when one part of the chemical reaction changes, other parts are also affected. Zebras eat grass and lions eat zebras. The zebras that can run the fastest can escape from the lions most often, but the lions that run the fastest can catch zebras most often. Zebras have genes that create bodies that can run fast, and lions have genes that create bodies that can run fast, because those are the kinds of genes whose chemical reactions are the most stable among the surrounding chemical reactions.
Evolution is natural selection, or, the adaptation to environmental pressures, because it’s an ongoing process of elimination in which whatever chemical reactions have gotten into an environment, and are the most stable in that environment, are the ones that keep happening. So not only are we descended from apes, or fish, or worms, or bacteria, if you go back far enough, we are descended from ultraviolet radiation shining on muddy water.