The Selfish Molecule
We have got used to speaking of the selfish gene, a unit much smaller than the individual organism (or the group or species). The genes create bodies that ensure their survival down the generations: the more effective a gene is at producing bodies that survive to reproduction the more copies of it will survive. The gene is thus the unit of natural selection. Of course, genes are not literally selfish, but they act as if they are, and the gene’s eye view affords the most illuminating perspective on the process of evolution (according to current orthodoxy). A gene consists of DNA, a complex molecule, famously shaped like a double helix. This molecule is made of other molecules, i.e. chemical entities—notably, phosphate, deoxyribose, adenine, guanine, cytosine, and thymine. These constituent molecules determine how DNA functions in duplication and hence in reproduction. Presumably they were naturally elected as “good” agents of heredity: they worked better than other molecules in facilitating the reproductive process. They build genes that can copy themselves and hence proliferate. If we think of replication before the evolution of bodies, when the earth just contained complex molecules that copy themselves, then the constituent molecules were the things that made for survival and reproduction. The molecule that gets copied is the one that makes for a good piece of DNA, i.e. one that can replicate in a hostile environment.
So why can we not go down one stage further in size and speak of the selfish molecule? The molecules build DNA that builds bodies that survive, and the bodies that survive ensure the survival of the chemical machinery that produces them. Thus it is not just the gene that is selfish but also the molecular components of the gene. We have selfish phosphate, selfish adenine, and selfish thymine. Like genes, these chemicals combine with other chemicals to produce viable hereditary material, viz. DNA—they are cooperative (as genes cooperate with other genes). But each type of molecule is in it for itself, since copies of it will only survive if it works well in the hereditary process. If the chemical fails to make a good body, it will tend to disappear from the pool of chemicals that help to make bodies. The chemicals that now compose DNA must have been good survivors in the past and are now fixtures on the scene. Just as we speak of the gene pool, so we could speak of the “molecule pool”, i.e. those molecules that form the material of organic reproduction.
There is no incompatibility in speaking of both genes and their constituent molecules as selfish; we are just looking at evolution from a different level (individual organisms are selfish too). But the molecule-eye point of view serves to show just how rooted in chemistry and physical replication the entire process is: it’s all about which chemicals enable themselves to be copied. Once molecules were able to replicate themselves the process of evolution by natural selection was off and running; and the replication is possible because of the basic chemical components involved. Those components survived that made good replicating macromolecules, and later actual bodies. It doesn’t matter that the molecules can exist outside of organisms; the point is that they found a safe home inside evolved organisms. It is the copying that matters—the capacity to multiply. The basic units of natural selection, at the physical level, are thus the molecular constituents of self-replicating macromolecules. The survival of the fittest applies at the level of the basic chemistry of DNA duplication. The chemical components of DNA are entities that have biological fitness, i.e. the possibility of differential survival. If another chemical took the place of adenine, say, by dint of some strange mutation, it would be safe to assume that it would not long survive, since it would likely introduce a breakdown of the chemical process whereby DNA replicates itself. The chemicals that make up DNA are the arms and legs of the genes: if you randomly mutate arms and legs you are apt to produce a biological disaster, and similarly with the chemical building blocks of DNA.
Dawkins likes to speak of genes as sitting inside survival machines, as if genes are passengers inside the bodily vehicle. Well and good: but can’t we also speak this way about genes and their chemical constituents? Isn’t a gene a survival machine for its component molecules? If it survives, they do; if it perishes, so do they. The gene survives depending on the body it produces, and the same is true of its chemical constituents. If a chemical is part of a “good” gene, it will find itself copied—as the chemicals that compose DNA are copied as it is copied. From the point of view of the several molecules their vehicle consists of strands of DNA—this is what gives them their immortality. Bodies house DNA and DNA houses molecules: the whole thing works because the molecules are good at their job, viz. generating copies of themselves. At any rate, they can do this once they cooperate with other molecules—just as genes need other cooperating genes in order to survive.
Can we push evolution down another level, to the level of atoms? Are there selfish atoms? I don’t think so, because atoms do not become more numerous through the mechanism of natural selection: they don’t need natural selection and organic vehicles in order to survive. They stay in existence even if the organism dies before reproducing. The universe would contain the same number and type of atoms even if life had never evolved. But the same is not true of organic molecules: these do depend on life to keep them going through time, at any rate in the quantities that we see. The universe contains more adenine and thymine now than it would have if life had never evolved; maybe it would contain none if life had never evolved. Compare crystals: we get more of them by replication than we would otherwise get, but the number of atoms doesn’t change. What is important about the molecules that make up DNA is that they too can become more or less numerous in the future, depending upon the bodies that they sit in. Bodies need genes that construct them well, and genes need chemicals that construct them well. Natural selection thus works at the level of organic molecules as well as genes. The world is replete with selfish molecules, composing selfish genes.