Science of Discworld III

rigorous testing. In this respect there is far more reason to take the theory of evolution seriously than any explanation of life that depends on, say, religiousfaith, because falsification is not high on the religious agenda. Theories, in that sense, are the best established, most credible parts of science. They are, by and large, considerably more credible than most other products of the human mind. So what these people are thinking of when they chant their dismissive slogan should actually be ‘only a hypothesis’.
    That was a defensible position in the early days of the theory of evolution, but today it is merely ignorant. If anything can be a fact, evolution is. It may have to be inferred from clues deposited in the rocks, and more recently by comparing the DNA codes of different creatures, rather than being seen directly with the naked eye in real time, but you don’t need an eyewitness account to make logical deductions from evidence. The evidence, from several independent sources (such as fossils and DNA), is overwhelming. Evolution has been established so firmly that our planet makes no sense at all without it. Living creatures can, and do, change over time. The fossil record shows that they have changed substantially over long periods of time, to the extent that entirely new species have arisen. Smaller changes can be observed today, over periods as short as a year, or mere days in bacteria.
    Evolution happens .
    What remains open to dispute, especially among scientists, is how evolution happens. Scientific theories themselves evolve, adapting to fit new observations, new discoveries, and new interpretations of old discoveries. Theories are not carved in tablets of stone. The greatest strength of science is that when faced with sufficient evidence, scientists change their minds. Not all of them, for scientists are human and have the same failings as the rest of us, but enough of them to allow science to improve.
    Even today there are diehards – not a majority, despite the noise they make, but a significant minority – who deny that evolution has everoccurred. Most of them are American, because a quirk of history (coupled with some idiosyncratic tax laws) has made evolution into a major educational issue in the United States. There, the battle between Darwin’s followers and his opponents is not just about the intellectual high ground. It is about dollars and cents, and it is about who influences the hearts and minds of the next generation. The struggle masquerades as a religious and scientific one, but its essence is political. In the 1920s four American states (Arkansas, Mississippi, Oklahoma, and Tennessee) made it illegal to teach children about evolution in public schools. This law remained in place for nearly half a century: it was finally banned by the Supreme Court in 1968. This has not stopped advocates of ‘creation science’ from trying to find ways round that decision, or even to get it reversed. Largely, however, they have failed, and one reason is that creation ‘science’ is not science; it lacks intellectual rigour, it fails objective tests, and at times it is plain nutty.
    It is possible to maintain that God created the Earth, and no one can prove you wrong. In that sense, it is a defensible thing to believe. Scientists may feel that this ‘explanation’ doesn’t greatly help us understand anything, but that’s their problem; for all anyone can prove, it could have happened that way. But it is not sensible to follow the Anglo-Irish prelate James Ussher’s biblical chronology and maintain that the act of creation happened in 4004 BC , because there is overwhelming evidence that our planet is far older than that – 4.5 billion years rather than 6000. Either God is deliberately trying to mislead us (which is conceivable, but does not fit well with the usual religious messages, and may well be heretical) or we are standing on a very old lump of rock. Allegedly, 50 per cent of Americans believe that the Earth was created less than 10,000 years ago, which if true says something rather sad about the most expensive education system in the world.
    America is fighting, all over again, a battle that was fought to a finish in Europe a century ago. The European outcome was acompromise: Pope Pius XII did accept the truth of evolution in an encyclical of 1950, but that wasn’t a total victory for science. 2 In 1981 a successor, John Paul II, gently pointed out that ‘The Bible … does