The Greatest Show on Earth

A Little History Of Science: The Greatest Show on Earth

Go for a walk in the countryside and you will find yourself among trees, flowers, mammals, birds and insects that belong in your part of the world. Go to a zoo and you will find exotic plants and animals from far away. Go to a natural history museum and there will be fossils, perhaps giant dinosaur skeletons, that are millions of years old. The person who taught us how all these living and fossil species are actually related was a quiet, modest man named Charles Darwin (1809–82). He changed the way we think about ourselves.

Carl Linnaeus named plants and animals with the idea that biological species are fixed. We still name them according to his principles. We can do this because, although we now know plants and animals do change, it’s very slow. A biological species has real meaning. But with species there is variation. Children may differ from their parents: perhaps taller or with a different hair colour, or a bigger nose. Young fruit flies that swarm around rotting fruit in summer also differ from their parents, but because of their size it’s hard to see. Easier to see are the differences between puppies or cats in a litter. What Darwin realised is that variations between parents and their offspring are very important, whether or not we see them. Even if we cannot always appreciate them, nature can, and does. Darwin’s road to this vital insight was full of adventure and quiet thought.

Darwin’s father and grandfather were successful doctors. His grandfather, Erasmus Darwin, had a theory of how plants and animals evolved, and wrote poems about science. Charles was a happy child, even though his mother died when he was eight. He discovered a love of nature and experimented with his chemistry set. He was only an average student at school. His father sent him to the University of Edinburgh to study medicine, but he was much more interested in natural history and biology. After the first surgical operation he saw made him physically sick, he knew he could never become a doctor. Darwin always remained extremely sensitive to suffering.

After his failure in Edinburgh, he went to the University of Cambridge to study for a basic arts degree, with the idea that he would become a clergyman. He passed his exams. Just. But Cambridge turned out to be vitally important because of the friendships he forged with the professors of botany and geology.

They inspired him to become a naturalist. John Henslow took him plant collecting in the Cambridge countryside. Adam Sedgwick went with him to Wales to study the local rocks and fossils. After this tour with Sedgwick, Darwin had graduated from the university and was at a loose end, not sure what to do next. He was saved by an unusual offer: would he like to become the ‘gentleman naturalist’ on a surveying voyage aboard the ship HMS Beagle, led by Captain Robert Fitzroy of the Royal Navy? His father said no, but his uncle convinced his father that it was actually a great idea. The voyage on the Beagle was the making of Charles Darwin.

For almost five years, from December 1831 to October 1836, Darwin was away from home as the ship sailed gradually around the world. He was seasick for much of his time at sea, but he also spent plenty of time on land, especially in South America. He was an outstanding observer of all kinds of natural phenomena: landscapes, people and their customs, and plants, animals and fossils.

He collected thousands of specimens and shipped them home, all carefully labelled. Today he would have written a blog, but he kept a wonderful journal, which he published after he came home. His Journal of Researches (1839) was immediately popular and remains a classic account of one of the most important scientific journeys ever taken. We know it as The Voyage of the Beagle.

Darwin’s ideas about evolution would be worked out in the future, but even then he was privately wondering how plants and animals changed over time. His Journal of Researches told its readers about three especially important things. First, while Darwin was in Chile, he experienced – from the safety of the Beagle – a violent earthquake that dramatically raised the level of the coastline by almost fifteen feet (4.5 metres). Darwin had his copy of Lyell’s Principles of Geology with him and was very impressed by Lyell’s idea that violent events such as earthquakes could explain the past. The earthquake in Chile convinced Darwin that Lyell was right.

Second, Darwin was struck by the relationships between living species and recent fossils of plants and animals. On the eastern side of South America, he found large living armadillos, and fossils that were similar: similar, but clearly not of the same actual species. He discovered many other examples, and added his own to those found by other naturalists.

Third, and most famous, were his discoveries on the Galapagos Islands. This group of islands is separated by hundreds of miles from the western coast of South America. Here there were some amazing plants and animals, including giant tortoises and beautiful birds, many of which were unique to a single island. Darwin visited several of the islands and carefully collected specimens. He met an old man who could tell which island a turtle came from, so specific was the appearance of turtles from these islands. But it was only after Darwin returned to England that he began to realise the significance of what he had found. A bird expert looked at the finches collected from the different islands, and found that they were actually of different species. Each island of the Galapagos was, it seemed, a kind of mini-laboratory of change.

Leaving South America, the Beagle sailed across the Pacific to Australia, then under the southern tip of Africa. It returned to England via another brief visit to South America. When the ship arrived back in England in 1836, Darwin had become a first-class naturalist, very different from the nervous young man who had set out. He had also acquired a scientific reputation at home through the reports, letters and specimens he had sent back.

He spent the next few years working on many of the things he had collected on the expedition, writing three books. He also married his cousin Emma Wedgwood, and moved to a large house in the Kent countryside. Down House would be his home for the rest of his life, the place where he would do his most important work. It was just as well that he liked to be at home, since he suffered from a mysterious illness and he was often unwell. Whatever his illness was – and we still don’t know what was wrong with him – he and Emma had nine children. He also wrote a steady stream of books and papers. One of these is the most important book in the whole history of biology: On the Origin of Species, published in 1859.

Years before that book was published, Darwin had begun keeping his private notebooks on ‘transmutation’. He began the first in 1837, soon after he returned from the Beagle voyage. In 1838, Darwin read Thomas Malthus’s Essay on the Principle of Population. Malthus, a clergyman, was mostly interested in why so many people are poor.

He suggested that the poor marry too early and have more children than they can look after properly. Malthus said that all species of animals produce far more offspring than can survive. Cats can have three litters a year, each with six or more kittens. Each year an oak tree produces thousands of acorns, and each acorn can become another tree. Flies can produce millions of young flies each year. If all the offspring of these plants or animals survived, and if this happened in the following generations too, the world would soon be completely overrun with cats, oak trees or flies.

Malthus believed that all these extra offspring were essential because there is so much wastage. Nature is harsh – it’s tough out there. When Darwin read Malthus’s essay, he realised that he had discovered a reason why some young make it, and some don’t. It would also explain why plants and animals change very gradually over long periods of time. Those that survive must have some advantage over their siblings, and there would be ‘the survival of the fittest’, or natural selection as Darwin called it. Darwin reasoned that all offspring inherit some traits from their parents, such as being fast runners. The offspring with the most useful traits were more likely to survive: they could run a bit faster, or had slightly spinier thorns. So those traits would be ‘selected’, because the less successful individuals, who did not have these traits, would not survive long enough to have offspring of their own.

Darwin realised that change in nature is very slow. But, he argued, we know that change can be much quicker when human beings are in charge of the process, selecting the traits they desire in their plants and animals. He called this artificial selection, and humans have been doing it for thousands of years. Darwin bred pigeons, and exchanged many letters with his fellow pigeon fanciers. He knew just how quickly the shapes and behaviour of their show pigeons could change, when the breeders carefully selected pigeons with certain traits for breeding chicks. Farmers had been doing the same thing with their cows, lambs and pigs. So had plant breeders when they tried to improve their crops, or produce more beautiful flowers. You know how very different a sheepdog is from a bulldog. It is easy to create variety in animals if the breeder selects the traits they desire.

Darwin saw that nature acts much more slowly, but, given enough time and the right environmental conditions, exactly the same thing happens. What he had learned of the birds and turtles in the Galapagos Islands illustrated how natural selection worked.

The local conditions – soil, predators, food supplies – were slightly different on each island. So the local plants and animals had adapted to the differing local circumstances. The beaks of the various kinds of finches had been ‘selected’ for the different things they could find to eat: seeds, fruit, or ticks that lived on the tortoises. In some cases, as Darwin had learned, the differences had become great enough to create different species, although all the finches were still closely related. Time and isolation had allowed significant change to occur, and new species had evolved.

Silently, Darwin read widely and collected many other observations. He wrote a brief sketch of his theory in 1838 and a longer version in 1842. But he didn’t publish his thoughts. Why? He wanted to be certain he was right. He knew he had a revolutionary view of the living world and that other scientists would criticise him severely if his account was not convincing. In 1844, Robert Chambers, an Edinburgh publisher and amateur naturalist, anonymously published his own version of species change. Chambers’ Vestiges of the Natural History of Creation created a sensation. ‘Transmutation’ became a hot topic. Chambers had gathered a lot of evidence suggesting that living species are the descendants of previous ones. His ideas were rather vague, and he had no real theory about how this had happened. He made many mistakes. His book sold very well, but was savaged by the leading scientists – the very people Darwin hoped to convince. So Darwin waited. He finished some important publications from the Beagle work, and tackled an unusual but safe topic: barnacles. Dissecting and studying these small sea creatures was difficult, but Darwin always insisted that it gave him valuable insights into a group of animals with a large number of living and fossil species, each adapted differently to the way they lived.

After the barnacles, Darwin at last returned to his great work. In 1858, when he was writing a long book that he was calling ‘Natural Selection’, the postman delivered disastrous news. From far-away Asia came a letter asking for Darwin’s opinion on a short paper. It was a brief account of the way natural selection could lead to species change over time. Darwin groaned. Its author, Alfred Russel Wallace (1823–1913), could have been summarising Darwin’s own slow and painful path towards that same conclusion.

Darwin’s friends Charles Lyell and Joseph Hooker, who both knew of his views on species, helped him out. They arranged for a joint presentation of Wallace’s and Darwin’s ideas at the Linnean Society in London. Nobody paid much attention to what was said at the meeting. Darwin was sick at home and Wallace didn’t even know about it – he was 8,000 miles away. But Wallace’s letter had persuaded Darwin that he must quickly write a summary of his ideas, instead of the long book he was working on. So On the Origin of Species was published on 24 November 1859. The publisher had 1,250 copies printed. They all sold in one day.

At the heart of his book were his two main ideas. First, natural selection favours the survival of useful traits, that is, characteristics that help individuals live and reproduce. (Artificial selection showed how human beings could dramatically alter the characteristics of plants and animals if they wanted to, illustrating how changeable plants and animals could be.) Second, natural selection, acting in the wild and over the long run, produced new species.

They evolved slowly over time. The rest of the book was a brilliant demonstration of how well these ideas explained the natural world. Darwin wrote about the relationship between living species and their closely related fossil ancestors. He described the geographical distribution of plants and animals throughout the world. He explained how geographical isolation (as in the Galapagos Islands) provides the conditions in which new species can develop. And he emphasised that the embryos of some animals were surprisingly similar to the embryos of others. Darwin’s Origin did for biology what Newton’s Principia had done for physics. It made sense of a vast number of things in the natural world.

Darwin’s biggest problem was inheritance: why offspring might be like their parents, and at the same time be slightly different from them and from each other. He read carefully and thought about it. He suggested some explanations, but he knew that heredity (genetics) was poorly understood, and he said so. He also knew that what was important was not saying how inheritance worked but that it did happen. On the Origin of Species created a stir. People wrote and talked about it. Some had good things to say about it, others criticised it.

Darwin simply kept working on it – he published six editions before he died. He developed his ideas, partly in response to criticisms, and partly because his own ideas continued to mature. As well as keeping the Origin up to date, he continued to write an astonishing number of other books on things that interested him: beautiful orchids, with their flowers adapted to the insects that pollinate them; plants that catch and digest insects; climbing plants that can cling to a wall; and even the humble earthworm. No wonder he was described as ‘a man of enlarged curiosity’. Nothing seemed to escape his notice.

The Origin didn’t say anything about human evolution, although Darwin knew that his insights were just as true for our own biological history. It was pretty clear to any reader of the first edition of the Origin that Darwin believed in the evolution of the human species, but he waited for more than a decade to say so openly, in The Descent of Man (1871). Darwin made biological evolution a valid scientific theory.

Some scientists were not convinced, but most were, even if they sometimes proposed their own versions of how and why it had happened. Many of the details of Darwin’s great work have been corrected by later scientific work. It wasn’t utterly perfect. It didn’t have to be – science is like that. But from his study and garden at Down House, Darwin ensured that we would never look at life on earth in the same way again. The evolutionary history of our planet is simply the greatest show on earth.