It seems to have been the geneticist T. H. Morgan, pioneer of fruit fly research, who first spotted the problem. He wrote early in this century: 'For it may be little more than a truism to state that the individuals that are best adapted to survive have a better chance of surviving than those not so well adapted to survive.''¹²

A tautology (or truism) is a self-evident, circular statement empty of meaning, such as 'Darwin was a man', or 'biology is studied by biologists'. The trouble with natural selection (and survival of the fittest) is that it seems to fall into this category.

Darwin supposed that an individual creature with a particular advantage - the 'fittest among its kind' would be naturally selected to pass on the advantage to its offspring. A horse with long legs, for instance, would be able to gallop faster than the rest, and escape from wolves or some other predator, and would survive to produced heirs. A' 'fit' creature, therefore, was one best able to carry out the functions that kept it alive – best adapted to its local environment and its way of life.

But in science, this is a speculation that can never be satisfactorily proved. The normal scientific method - the test of observation and experiment - cannot be applied to single rare events that have happened in the past. Any number of other circumstances might have led to the death of the horse with long legs. Why shouldn't the wolves have eaten it when it was young before it was able to run so fast? Or eaten old horses, so that the speed of the long-legged horse would have been unnecessary? Or might it not have died from a heart attack, brought on by exhaustion from galloping so fast?

Even Thomas Huxley admitted that Darwin had not proved that natural selection automatically produced new species, only that it 'must' have done so; actual proof was unobtainable. He added disarmingly that even if natural selection should turn out, in the fullness of time, to be an inadequate explanation, Darwin would still be regarded by posterity as a thinker as eminent as Copernicus or Newton. In this, of course, he was right. It takes a moment or two to realize that Huxley, by dismissing in advance the need for evidence, converted a working hypothesis into an established theory without going through the accepted scientific procedure.¹³

Neither Darwin nor Huxley nor any other evolutionist of the time could define a criterion for fitness which would inevitably be naturally selected in an individual creature. Whether the long-legged horse had been fit was decided in retrospect, after it had died. Darwinism, as Darwin wrote it, could be simply but nonsensically stated: survivors survive.

Which is certainly a tautology; and tells us nothing about how species originate, as even Darwin's supporters admit. Ernst Mayr wrote that 'Darwin failed to solve the problem indicated by the title to his work. Although he demonstrated the modification of species in the time dimension, he never seriously attempted a rigorous analysis of the problem of the multiplication of species.'¹⁴ George Simpson wrote in 1964 that 'the book called The Origin of Species is not really on that subject'.¹⁵

Panel 17

Is natural selection meaningless?

Most biologists, while admitting an element of tautology in the term natural selection, nevertheless think that it still has true scientific value. Darwin discussed the problem at some length in correspondence with the American botanist Asa Gray, and wrote that 'natural selection' was a convenient phrase for expressing a much more complex line of thought.

With the hindsight of our modern knowledge of genetics, the logic of Darwin's case might be expressed as follows. All giraffes alive a thousand years from now will be the descendants of giraffes alive today. Therefore giraffes alive today make up one hundred per cent of the ancestry of future generations. Giraffes, however, have many different sorts of genetic make-up, and 'fit' giraffes will make a numerically disproportionate contribution to the ancestry of the future population. It is not simply that they will produce more offspring, but rather that they have a better net likelihood of living and reproducing. So there is a statistical probability that the favored genetic types will give birth to offspring of their own kind that will survive to the age of their parents when they were born.

Stephen Jay Gould, in Ever Since Darwin, does not agree that Darwin himself solved what natural selection really meant - 'the theory of natural selection did not triumph until the 1940s'. But in its neo-Darwinian form, he thinks the term is now satisfactorily defined. His key point is:

Certain morphological, physiological, and behavioral traits should be superior a priori as designs for living in new environments. These traits confer fitness by an engineer's criterion of good design, not by the empirical fact of their survival and spread. It got colder before the woolly mammoth evolved its shaggy coat … The essence of Darwinism lies in its claim that natural selection creates the fit … It preserves favorable variants and builds fitness gradually.²²

The woolly mammoth, now firmly extinct, is a curious example to demonstrate survival of the fittest.