Correction to this article

THE miracles of nature are everywhere: on landing, a beetle folds its wings like an origami master; a lotus leaf sheds muddy water as if it were quicksilver; a spider spins a web to entrap her prey, but somehow evades entrapment herself. Since the beginning of time, people who have thought about such things have seen these marvels as examples of the wisdom of God; even as evidence for his existence. But 200 years ago, on February 12th 1809, a man was born who would challenge all that. The book that issued the challenge, published half a century later, in 1859, offered a radical new view of the living world and, most radical of all, of humanity's origins. The man was Charles Robert Darwin. The book was “On the Origin of Species”. And the challenge was the theory of evolution by natural selection.

Since Darwin's birth, the natural world has changed beyond recognition. Then, the modern theory of atoms was scarcely six years old and the Earth was thought to be 6,000. There was no inkling of the size of the universe beyond the Milky Way, and radioactivity, relativity and quantum theory were unimaginable. Yet of all the discoveries of 19th- and early 20th-century science—invisible atoms, infinite space, the inconstancy of time and the mutability of matter—only evolution has failed to find general acceptance outside the scientific world. Few laymen would claim they did not believe Einstein. Yet many seem proud not to believe Darwin. Even for those who do accept his line of thought his ideas often seem as difficult today as they were 150 years ago.

The origin of the Origin

The idea of evolution by natural selection is not hard to grasp. It just requires connecting some uncontentious propositions. These are that organisms vary from one another, even within a species, and that new variation can arise from time to time; that some of this variation is passed from parent to offspring; and that more individuals are born than can exist in the available space (or be sustained by the available resources). The consequence is what Darwin described in his book as a “struggle for existence”. The weakest are eliminated in this struggle. The fit survive. The survivors pass on their traits to their offspring. Over enough time, this differential transmission of characters will lead to the formation of a new species.

Darwin was neither the first to recognise these simple ideas nor to put them together. Thinkers as far back as Empedocles, a Greek philosopher born in 490BC, are known to have suggested that natural selection might explain why animals were adapted to their surroundings. The idea of the struggle for existence has been traced as far back as al-Jahiz, a Muslim theologian and scholar born in Basra around 776. And the idea crops up again in the works of Thomas Hobbes, a 17th-century philosopher, and Erasmus Darwin (Charles's grandfather), who lived in the 18th.

By the beginning of the 19th century, the idea of evolution was in the air. There was an emerging acceptance that species were unstable. The botanists could see it in their hybrids. But what was missing was the mechanism.

At the start of the 19th century Jean-Baptiste Lamarck, a French naturalist, thought he had found it. He recognised that species were mutable, and he also proposed that traits could be inherited. His error was to suppose that individuals lost characteristics that they did not need in life and developed ones that they did—and that it was these changes that were passed to their offspring. A giraffe, for example, might grow a longer neck because it was useful for eating food that other giraffes could not reach. Its progeny would then inherit the attribute. It was a nice idea, but Lamarck was wrong. Acquired characteristics cannot be transmitted in this way.

In the end, the answer came not from biology but from economics. In 1798 Thomas Malthus wrote “An Essay on the Principle of Population”. Malthus argued that natural populations grow at an exponential rate, whereas the increase in food supply is linear. In other words, more individuals are born than can possibly survive. His book popularised what was, in fact, an old idea, at just the right time for biology. After reading Malthus, both Darwin and Alfred Russell Wallace, a British naturalist, independently put the pieces of the puzzle together and dreamed up evolution by natural selection.

They both saw what Lamarck had failed to, that the struggle for existence in a crowded world, with its winners and losers, was the force that would ensure the survival of the plants and animals carrying the best traits. Darwin's autobiography records his eureka moment: “I happened to read for amusement Malthus on population, and being well prepared to appreciate the struggle for existence…it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.”

The first to see selection

It turns out, though, that even Darwin and Wallace were not the first to put the pieces together. In 1813 William Charles Wells, a Scottish doctor, had presented a paper on race to the Royal Society, in which he introduced the idea of natural selection to explain why people might vary in skin colour in different climates. And in 1831 Patrick Matthew, a Scottish landowner, provided a description of natural selection in an appendix to a book about growing the best trees to make warships.

Nevertheless Darwin and Wallace are remembered, whereas Wells and Matthew are not, because they made the idea explicit and both wrote papers devoted to it. These they presented to the Linnean Society in London in 1858. Darwin, moreover, is more famous than Wallace because he had devoted the previous two decades to the painstaking accumulation of evidence in support of the theory from areas as diverse as embryology, artificial breeding, geography, economics and geology, and so was able to go into print the following year with “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life”, to give the book's full title.

Darwin's theory explained why species were so well adapted to their environment and how new species would form. It suggested that all living things were related, from the beetle to the lotus, and that everything descended ultimately from a single common ancestor. Evolution thus removed the need for divine explanations of diversity and, along with evidence emerging at that time of the extreme age of the Earth, it further suggested that the wider universe might also owe nothing to divine intervention and everything to natural laws. Darwin understood all of this and was greatly troubled.

That trouble continues today. In the United States a Gallup poll conducted last year found that only 14% of people agreed with the proposition that “humans developed over millions of years”, up from 9% in 1982. Acceptance of evolution varies around the world, with the most ardent believers being in Iceland, Denmark and Sweden (see chart). In general, as you might expect, a country's belief in evolution is inversely correlated with its belief in God. But there is an interesting twist.

Gregory Paul, an independent researcher on evolution, and Phil Zuckerman, a sociologist at Pitzer College in California, have argued controversially that a belief in God is inversely correlated with the level of what might be described as the intensity of the struggle for existence. In countries where food is plentiful, health care is universal and housing is accessible, people believe less in God than in those countries where their lives are insecure. A belief in God, and rejection of evolution, they suggest, is most valuable in those societies that are most subject to Darwinian pressures.

Making science work

Be that as it may, many aspects of modern science could not work without accepting evolution. Darwin's ideas touch every corner of biology and medicine. They have also had an impact farther afield, in areas from art to politics. And their impact has been practical as well as theoretical. Both software engineers and drug developers, for example, often make use of evolutionary thinking when designing their products.

Economics, too, may be helped by Darwin. Ideas about “rational” economic man are being overturned by new ones from a discipline called behavioural economics. Rather than assuming that individuals faced with economic decisions will comport themselves in what “classical” economists regard as a rational manner—ie, to maximise their future wealth—behavioural economics tries to study how real people actually behave.

What is surprising is the degree to which human beings are not rational, and how the reasons for this are likely to involve Darwinian explanations. Take, for example, a phenomenon called the endowment effect, which is the tendency most people have to value objects they already own more highly than similar ones they have never owned—and, consequently, to be more reluctant to trade them than a classical economist would predict.

Because this effect has been observed in three primate species, most recently in a study of chimpanzees, it suggests this effect has evolutionary roots. Its strength seems to relate to the evolutionary salience of the item in question. People may be reluctant to trade goods related to food and mating because in the recent evolutionary past it meant parting with a known object in exchange for an uncertain proposition.

Another example of economic behaviour that may have deep evolutionary roots is the “herd” mentality that contributes to financial bubbles. In the past, copying the neighbours would have been helpful—in order to avoid danger or to find food. In today's financial systems, however, it can create instability. The instinct to follow the herd can be rationalised as rational, so to speak, since everybody benefits in the short term by forcing the price up. But it does not look so rational when the instability is exposed by an external shock and the market crashes. In fact, at least part of what seems to be going on is that everyone instinctively feels compelled to copy the others, rather than making an independent assessment of the situation.

Whether the mystery is why people are so averse to risk, unable to estimate the time needed for a given task, or give different answers to the same question depending on how it is framed, there is a fair chance that the explanation will, at some point, involve evolution. To understand human behaviour properly, the world needs Darwin. Some have said it is the best idea that anyone ever had. If it isn't, it certainly comes close.

Despite so much evidence, evolution remains difficult to accept because it implies everything living is largely accidental. Stephen Jay Gould, an American evolutionary biologist, who died in 2002, argued that misunderstandings about Darwinism were rife not because the theory is difficult to understand but because people actively avoid trying to understand it. He thought a misunderstanding about progress was the problem.

Completing the revolution

People are comforted by the idea of a designed and harmonious natural world, with themselves at the top. It is hard to accept that such harmony has arisen as an accidental consequence of a brutal system with no principles beside the one that every individual is striving for reproductive success. It is depressing to think that life is purposeless and that evolution has no higher destination.

This criticism applies to many believers in evolution who are not actually workers in the field, as well as those who reject the theory. It is a commonly held view that evolution implies progress, even among those who believe in natural selection.

Most biologists disagree. They argue, along with Gould, that evolution has no fixed direction. A creature can become fitter by getting more complex. But it can also become fitter by getting simpler. It all depends on the circumstances. The undoubted increase in average complexity in the fossil record is, according to this view, an accident of the fact that life started simple and therefore had only one direction to go in. Changes that lead to complexity are more obvious than those that lead to simplicity, since they create something that was not there before. This does not mean, however, that they are more numerous.

Gould's view was thus that the evolution of human intelligence while not exactly an accident, since it was a response to a long series of circumstances, was certainly not a foregone conclusion. If that series of circumstances had been even slightly different, there would have been no egg-headed Homo sapiens.

That view is being questioned. For example, in a study published last year in the Proceedings of the National Academy of Sciences a group of researchers looked at crustaceans (crabs, shrimps, woodlice and so on) over the past 550m years and found far more examples of groups of species evolving towards complexity than in the other direction. Matthew Wills of the University of Bath, in England, commented at the time that it was the “nearest thing to a pervasive evolutionary rule that's been found.” In this study, the only crustaceans that became simpler were either parasites or those living in remote habitats, such as isolated marine caves.

Simon Conway-Morris, a palaeontologist at Cambridge University, in England, is the champion of a new interpretation of evolution—one that challenges the view that it is largely governed by the accident of circumstances. Unlike Gould, he thinks that if evolution were replayed from the beginning, a lot of things would turn out the same.

Dr Conway-Morris has arrived at this view from a detailed study of what is known as convergent evolution. Darwin himself was intrigued by this phenomenon, in which different groups of organisms independently evolve similar solutions to similar problems, whether these solutions are teeth, eyes, brains, ecosystems or societies. Where other biologists have noted such convergences as “remarkable”, Dr Conway-Morris believes they actually tell a broader story.

His argument is that, given the nature of physics and chemistry, there may be only a limited number of ways in which things can work. Evolution will be channelled into these successful paths, and thus does have trends. Two of these, he thinks, are towards complexity and intelligence. He adds that things “don't just happen in chemistry”. They happen because of pre-existing causes. Whether it is the molecules of crystallin that are used to build an eye or the haemoglobin that makes blood carry oxygen, the nature of molecules themselves means that evolution is more likely to follow a path determined by their basic structure. Evolution is a mechanism, and it works within rules.

Dr Conway-Morris's view of the world may or may not turn out to be correct. If it is, it may prove more palatable to some people than the current interpretation of the biological world as ultimately materialist and purposeless.

Darwin himself was deeply troubled by his materialist thoughts and what they meant. He considered how thoughts and emotions were simply secretions of the brain. From his correspondence it seems his religious beliefs never reached a fixed position, but he was sensitive to the extent to which his ideas could upset others. He even devised a diplomatic answer that avoided challenging the existence of God. When asked about the origins of emotions, instincts and degrees of talent, he noted, “say only they are so because brain of child resembles parent's stock”.

More to know

Dr Conway-Morris is not convinced by Gould's arguments. He thinks there is unfinished business to deal with. On the source of moral systems and consciousness, he says, “we are nowhere near an answer”. In his world, science can explain the beetle, the lotus leaf and the spider's web, but not why they appear beautiful to people. Others think that the explanation is memes, the cultural equivalent of genes in which ideas replicate through the human desire to imitate.

In some ways, though, it does not matter whether humanity's evolution was entirely random or was predictable in its general form. For people do, now, have a united evolutionary common purpose: to halt that natural selection in its tracks. The species has evolved to the point where it understands itself, and can seek to escape the brutal handcuffs of nature and end the struggle for existence. The beginning of that understanding was provided by Darwin, and the application of Darwinism will be an important part of the process. That gives people every reason to celebrate his 200th birthday.





Correction: In an earlier version of this article we said that in the United States a Gallup poll found that only 15% of people agreed with the proposition that "humans developed over millions of years", up from 8% in 1982. The figures have been corrected: they are 14% and 9% respectively.