Natural selection

Comments invited on this first draft of bit of the humanism book. It would be easy to get some detail about the science wrong. Please offer corrections or suggestions, however minor…

Another popular argument for the existence of God is the teleological argument or argument from design. Arguments from design begin with the observation that the natural world, or items within it, appears to have certain remarkable features – such as order and purpose – and conclude that God is the only, or at least the best available, explanation of those features.

Perhaps the best-known argument from design is that presented by William Paley in his Natural Theology, published in 1802. Paley argues that, were one to find a complex object such as a watch lying on the ground, it would be unreasonable to suppose that the watch came to exist by chance, or that it had always existed in that form. Given the clear purpose of the watch – to tell the time – and its highly complex construction geared to fulfilling that purpose, it is reasonable to suppose the watch was fashioned by an intelligent being for that purpose. But if that is a reasonable conclusion to draw in the case of a watch, then surely it is reasonable to draw the same conclusion in the case of a work of nature such as the human eye, which also has a purpose for which it is intricately and exquisitely engineered. That intelligent designer, supposes Paley, is God.

That a biological organ such as the human eye must have some sort of designer was accepted by very many, including even the scientist Charles Darwin, up until the Darwin developed his own alternative explanation of the existence of the eye – a theory that explains how the eye might evolve gradually over many millions of years without the aid of any intelligence.

The mechanism Darwin realized could account for the gradual evolution of the eye is natural selection. When living organisms reproduce, their offspring may differ slightly in inheritable ways. Plant and animal breeders take advantage of these chance mutations to breed new strains. For example, a dog breeder might select from each generation of a dog those that are largest and least hairy, eventually producing a whole new breed of huge, bald dog.

Darwin’s great insight was to recognise that the natural environment in which organisms are located will, in effect, also select among offspring. Organisms with a chance mutation that enhances their ability to survive and reproduce in that environment will be more likely to pass that mutation on. Organisms with a mutation that reduces its chances of surviving and reproducing in that environment will be less likely to pass it on. And so, over a many generations organisms will gradually adapt to their environments. Under certain condition, a whole new species may emerge.

Darwin called this mechanism “natural selection”, contrasting it with the “artificial selection” used by dog and plant breeders. Unlike artificial selection, natural selection does not require an intelligent mind to guide the selection process towards a particular end. Selection is now taken care of entirely by blind, unthinking nature.

There is overwhelming fossil and other evidence that the human eye did, indeed evolve slowly and gradually over millions of years, beginning perhaps with the chance appearance a single light sensitive cell in an organism living many millions of years ago, and that natural selection is indeed the main mechanism that drove this process. Indeed, eyes provide such obvious survival value to organisms that they have evolved independently at least forty times.

The discovery of the mechanism of natural selection led Darwin to reject Paley’s argument from design. Darwin wrote:

The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection has been discovered.[REF4]

While the development of Darwin’s theory of natural selection, and, later, the theory of genetics (including the theory of genetic drift, another mechanism driving the process of evolution), resulted in a decline in the popularity of arguments from design, such arguments have recently been making something of a come-back. Two popular, more recent variants of the argument from design are outlined below.