When Einstein published his general theory of relativity in 1916, he pointed out three ways it could be tested. One was that a ray of light coming from a distant star on a path close to the sun would be bent towards the sun, at a particular angle. If this did not happen, then his theory was mistaken, he said. This is the classic way that genuine science deals with theories: it puts them to the test. Einstein did not propose a way his theory could be proved, but only a way it could be dis proved. If it survives the test, then to that extent it has been supported or corroborated, but there can always be further tests, which it may possibly fail. Scientific theories are almost never proved absolutely and for all time. As it happened, when this theory of Einstein’s was put to the test, by the British scientist Arthur Eddington and his team, observing a lunar eclipse in 1919 from Africa and Brazil, they found the effect Einstein had predicted did actually take place, and it has continued to survive all subsequent tests. So his theory is universally accepted by physicists. But it must be expected that eventually, one of these days, if only in the far distant future, exceptions to it will be discovered, requiring a change in the theory or a new theory.
Scientific theories have to be tested indirectly, through their effects; they cannot be tested directly, because they are statements of universal rules or laws, applying to all instances of a particular event. To be useful as a test, the effect must follow from the theory of necessity. It is no use pointing to an effect that according to the theory might or might not take place. It must be an effect that will necessarily take place if the theory is correct. Also, the effect must be definite, and observable.
In order, not to prove, but just to corroborate Darwin’s theory, the same procedure would have to be followed. We would have to find some definite effect which followed of necessity from the theory, and observe to see whether it happened. But is this possible in this case?
There is a difference between a fact and the explanation of that fact. Evolution, the fact that some species develop after, and in some way out of, earlier species, is clear from the fossil record, and was accepted as a fact long before Darwin. What was not clear at the time was the explanation of this fact. A number of different explanations had been put forward, but none of them conformed to the requirements of a scientific theory. Darwin’s achievement was to put forward the first explanation that did so conform. (Darwin’s theory, like the concept of evolution itself, does not apply to the origin of life, but only to what happens once there are living things.)
Darwin’s theory makes the following statements:
- Existing species develop varieties by chance (e.g. some brown squirrels are born red, perhaps, and eventually form a red tribe or ‘variety’ within the species);
- The different varieties must struggle for existence;
- Only the fit will survive;
- Those that survive will hand their successful qualities on to their offspring, and so eventually, when enough new qualities have been handed on, a new species will emerge.
The necessary effect would be the emergence of a new species. This would have to be predicted before it happened, or before it was known to happen. But this is extremely difficult, if not impossible, because of the complexity of the struggle for existence. How can we know, ahead of time, that some particular feature of their environment, rather than some other feature, will threaten their existence?
The first step in testing Darwin’s theory is to predict a definite variation, the emergence of a definite new variety out of the existing ones. Some people believe this has happened in the case of Darwin’s finches in the Galapagos Islands. It is true that there are many varieties of these finches there, which differ in the size and shape of their beaks. But has it actually been predicted , before the event, that a particular, definite variety would give rise to another particular, definite variety? This is not clear, despite the celebrated work of Peter and Rosemary Grant.
Even if this did happen, however, it would still be necessary to predict the emergence of a definite new species out of the definite old species. What is a new species? While anatomical features often play a role in this decision, the basic test is whether the two varieties, old and new, are capable of having fertile offspring from intercourse. This is even less clear in the case of the finches, because different strains seem to have separated and then come together again over time. So far there has been no corroboration of Darwin’s theory that could be considered at all comparable to that of Einstein’s theory. And even if it were corroborated, a corroboration is only support, not a strict proof.
Even if Darwin’s explanation were somehow proven true, however, that would not necessarily end the question. Science cannot use supernatural explanations, and its explanations are always reductionist, because science follows the principle of simplicity, or economy, otherwise known as Ockham’s Razor: the simpler explanation should always be preferred. This is a rational principle, but there is no guarantee that the simpler explanation is always the true one. When we are dealing with human beings, the simpler explanation is often not the true one. The features most distinctive of human beings are mental ones, that can never be verified by scientific testing. When science (the true, physical sciences) looks at a human being, it can see only a collection of material organs, it can never discover mind, or intention, or free will, or responsibility, or guilt, or innocence, because these are never the simpler explanation, which is always material and mechanical. Two thousand years ago Socrates complained about the scientists of his day that when he asked them for an explanation of the fact that he was sitting down, all they gave him was a mechanical explanation, that he was sitting down because his bones were doing this, and his muscles were doing that, and they made no reference to the real explanation, which was that he was sitting down because he intended to sit down.
Once living things exist, Darwin’s theory can explain everything else about their structure. It is universally accepted by scientists, not because it has been proved true, but because it is a genuine scientific theory, and because there is no other genuine scientific theory to compete with it.
Intelligent design does not compete with it, for the reason we have just seen, that intelligence is never the simpler explanation. Proponents of intelligent design argue that in some cases it is the simpler explanation. But this shows merely that they do not grasp the explanative power of Darwin’s materialist and reductionist theory.
We are left, then, with a paradoxical situation where
- we have no serious scientific alternative to Darwin,
- but Darwin has not, strictly speaking, been proved true, and probably can never be,
- and even if it were, that would not necessarily rule other explanations out as true.
Science cannot discover intelligence anywhere in the world, either in us or in nature. But that does not mean intelligence does not exist, either in us or in nature.