Science is the most wonderful combination of common sense and things that seem counterintuitive. The history of science helps explain why the common sense and experiences of our daily lives seem increasingly remote from what contemporary science suggests is actually going on. The more we know, the more mysterious the universe actually seems.
PLANETS AND ATOMS
Take an obvious counterintuitive example first. The sun rises in the east each morning, and sets in the west. We can see it move each day, assuming there are clear skies. It's thus small wonder that all ancient cosmologies placed the earth at the centre of things and had the sun moving sedately around us each day. The problems -- why there were seasons each year, or why the planets didn't always behave as they ought to -- were relatively minor when compared to what we could see with our eyes each day. Consequently, when the Polish astronomer and priest Copernicus (1473-1543) published in the year of his death a book stating that the sun is actually the center, and the earth revolves around it, it is not surprising that his ideas were greeted with scepticism. Today, we 'know' that the earth revolves around the sun, even if we 'see' the reverse each day. Further, we know that neither the sun nor the earth is at the center of the universe.
We also 'know' that tables and chairs, water and our bodies, are all composed of atoms. Although we can't see them, their existence seems less counterintuitive than the sun and earth dilemma. After all, we can grind up things to a pulp, and then grind some more. The convenient limit of how far this mechanical process could go can easily be called an 'atom'. A number of ancient Greek philosophers (today's 'scientists') argued for their existence more than 2,000 years ago. These natural philosophers were always in the minority, since most people believed that a world composed of 'atoms and the void' would be lifeless and without direction. As chemistry became more precise during the period of the Scientific Revolution, roughly 1500-1700, units of matter called 'corpuscles' were increasingly invoked to explain the regularity of what happened in controlled situations in the laboratory.
The modern 'atom' was the brainchild of a Quaker chemist John Dalton (1766-1844). His atom bore little resemblance to that of contemporary chemists, but it did explain much about both 'elements,' and the reactions that they can participate in. He argued that the elements, so central to Antoine Lavoisier's (1743-94) chemical vision, are each composed of identical atoms, so that things like carbon, magnesium, and sulphur, are different because the atoms of which they are composed are different from those of other elements, but similar to those of their kind. Dalton's ideas gave chemists a base from which to work, and it helped them make sense of the things that they observed with great regularity in their laboratories. This common sense for chemists also related to what we can observe in the everyday world.
THE SPECIES PROBLEM
Common sense might also tell us that biological species are constant. Oak trees always produce acorns that produce other oak trees, and cats always give birth to kittens. We say that members of a group of organisms that reproduce together, those offspring in turn successfully reproducing, belong of a species. The species concept is of crucial importance to biology, so important that it was the principal subject of the most important book ever written in the field: On the Origin of Species (1859). Charles Darwin (1809-82) was hardly the first person to argue that, given time and the right circumstances, one species of plant or animal can transmute into another. What he did better than anyone before was to gather an enormous range of evidence -- on the geographical distribution of plants and animals, on the meaning of the fossil record, on embryological development and the analogies between closely related species. Even more important, he offered a mechanism on how this could slowly happen over time. This was his notion of 'natural selection', based on two easily observable classes of facts. The first, called artificial selection, drew on the extensive literature on plant and animal breeding, whereby human beings selected particular characteristics possessed by a plant or animal -- beak shape, seed size, capacity to make milk -- and by carefully breeding these individuals, could in a few generations produce animals or plants dramatically different from the original ancestor. Darwin himself bred pigeons, but dogs, cows, sheep and all kinds of animals had been produced over the years that possessed far different characteristics than their ancestors had. These variations were inherited, a key feature of his thinking.
The second aspect of natural selection was also easily grasped. It had been formulated in the late 1790s by the Rev Thomas Malthus (1733-1834). He called it the 'principle of population,' and it was based on the observation that all organisms -- plants and animals alike -- can produce far more offspring than can actually survive. Oak trees, flies, rabbits (and human beings) could completely overrun the earth, were all their offspring to survive and in turn reproduce, over the generations. Darwin recognized that, in the wild, only those organisms best fitted for their environment made it through to reproduce. This 'survival of the fittest,' as it was called, was natural selection in action, and it could change organisms slowly over time -- making them better camouflaged, so to escape predators, or stronger and faster, the more efficiently to catch food or attract mates. Darwin identified many instances of this evolutionary mechanism and argued that, with time and circumstance, the descendants of an organism might be so different that they would be unable to breed with their ancestors: they would be new species.
What Darwin did was to invite his readers to think about the earth and its plants and animals over a very long period, and use what could be observed in the short term to think about a much longer period. He showed how many things in the living world - the adaptations of animals, the close relationships between living species and fossils of extinct animals found in the same locations, and the remarkable features of the developing embryo - were difficult to explain, except through what he called 'descent with modification.' We now know a great more about evolution than Darwin could have: science always changes from generation to generation. But Darwin's central ideas still have currency in modern biology, and as Theodosius Dobzhansky (1900-75) summarized it: 'Nothing in biology makes sense, except in the light of evolution.'
SCIENCE AND CHANGE
'Common sense' alone might never have penetrated any of my three examples, perhaps especially, the earth revolving around the sun, rather than the reverse. That's the one phenomenon we can actually see. But atoms, evolution and much else are part of a scientific edifice that is coherent and consistent. It constantly changes: we know far more about the universe than Copernicus could with his naked-eye observations. Our atom is nothing like Dalton's, and a whole range of modern discoveries have added substance to Darwin's ideas. Things, it seems, are not necessarily what common sense tells us they are, they are merely what they are. At the same time, science and its technology have produced the power and ingenuity that drives the modern world of jet airplanes, mobile phones and computers. The history of science teaches us that explanations change, and our ones may not be exactly the ones that our grandchildren will hold. But history also teaches us that science is the best means we have of understanding our world.