Now that the Pope has officially endorsed the theory of evolution, this is a good time to correct some misunderstandings about how evolution works, namely, the process of natural selection.
The term “natural selection” seems to imply Mother Nature pointing a gnarled finger at some hopeful monster and saying, “I think I’ll keep that one,” sort of a mirror image to the intentional selection for optimum traits observed in animal breeding.
Darwin reasoned that if an individual’s unique characteristics gave it a survival advantage in a changed environment, and those traits were heritable, the characteristics would gradually spread throughout the population. Natural forces are “selecting” for advantageous traits of individuals rather than breeders. Conversely, if some heritable trait makes an individual less successful in surviving relative to others in the population, then that trait would gradually disappear from the population (selected against).
In most discussions of natural selection, the focus is on characteristics of adults. Certainly, Darwin based his work on observations of adult finches and their feeding habits. But it should be quite obvious that selection acts at every stage in an individual’s development.
Proper development depends on specific genes being turned on and off at specific times. What turns genes on or off are the different chemical substances contained in the intracellular environment. This micro-chemical environment is greatly affected by events outside the cell: changes in temperature, presence of other chemical substances, more or less light than is appropriate, and physical forces, among many other things.
Most people probably associate natural selection with the phrase “survival of the fittest.” It is easy to picture animals fighting to the death, proclaiming the victor to be the “fittest.” Actually, that’s not how it works.
“Survival” means surviving long enough to reproduce. Clearly, any heritable characteristic that limits an individual’s ability to reproduce will be selected against. Furthermore, if a trait does not manifest itself until after the individual has produced offspring, that trait cannot be selected, either “for” or “against.”
“Fittest” is defined not by which characteristics lead to wining more fights, but by which characteristics result in leaving more offspring that survive to reproduce more offspring, while using fewer resources and consuming fewer calories than other individuals in the local population
So when does natural selection occur? At every point in development, from the joining of the sperm and egg, through the first division of the fertilized egg cell and all subsequent development, until the adult individual ceases to reproduce. (Except for the sperm and egg thing, the same forces work on non-sexually reproducing species.)
It is no wonder that species have evolved reproductive strategies that stabilize the environment in which their embryos develop: some lay eggs in the sand, some sit on eggs in a nest, some carry the fertilized eggs inside the mother. Furthermore, one could argue that, in the course of evolution, the accumulation of cells in the process of development that creates what we call “adult” organisms is an adaptation of single cell organisms to protect themselves and to facilitate their reproduction.
This, by the way, answers the question: “Which came first, the chicken or the egg?”
Obviously, the egg came first. The chicken is the egg’s way of reproducing itself.