Ordering the World

A Little History Of Science: Ordering the World

Our planet is home to a bewildering variety of plants and animals. We still don’t know exactly how many insects or sea creatures there are. We rightly worry that the human race is reducing their number. ‘Endangered species’, such as giant pandas and Indian tigers, are in the news almost every day. For us as concerned human beings, the important word in ‘endangered species’ is endangered, but for scientists, an equally significant word is species.

How do we know that the giant panda is not the same kind of animal as the grizzly bear, or the wildcat different from the pet cat we stroke? Adam, in the Bible’s Book of Genesis, is given the job of naming the plants and animals in the Garden of Eden. All human groups have some way of organising the living world around them. All languages have names for the plants and animals people use, whether they are cultivated, gathered or provide transport, meat, hides or milk.

During the seventeenth and eighteenth centuries, European explorers began to bring back many new kinds of plants and animals from exotic parts of the world: from North and South America, Africa, Asia, and then Australia and New Zealand, as well as islands in the world’s oceans. Many of these new creatures were wonderfully different from the familiar plants and animals of the Old World, but when they were closely examined, a lot of them were not all that different. For example, elephants found in India and Africa were so similar that the same name seemed appropriate.

Yet, there were small differences. How should we account for these slight differences, and for the rich variety of nature? From Antiquity, there had been two basic answers to this question. One was to assume that nature was so bountiful that it was not surprising that many, many new kinds of plants and animals were being found in remote parts of the world. These new discoveries were thought to be simply filling the gaps in what naturalists called the ‘Great Chain of Being’, an idea we met way back. Those who believed in the Chain of Being argued that God was so powerful that he created every creature that could possibly exist.

They weren’t surprised to find animals that combined characteristics of other animals, like whales and dolphins in the oceans, which looked like fish, but breathed and gave birth like land animals; or bats, which looked like birds in that they had wings and flew, but didn’t lay eggs. This was because these naturalists thought all the curious aspects of plant and animal life could be explained as being part of the Chain of Being. The idea of the ‘missing link’ in this chain, which you might have heard about when an important new fossil is found, has been around for a long time.

The second answer was to assume that God originally created each kind of plant and animal, and that the vast variety of nature we can see around us is the result of generation after generation producing their young. Oak trees produce saplings from their acorns, just as cats give birth to kittens, which grow up to have more kittens, and so on. And with each generation, or hundreds of generations, or thousands, the trees and cats would become more diverse. That is, the vast variety of nature was to be understood as being caused by changes that happened over time, though each plant or animal could still be said to relate to an original design. To map out all of the original plants and animals would display God’s plan, as a ‘tree of life’.

During the eighteenth century, two naturalists dominated thinking on these issues, and they happened to reflect these two differing approaches. The first was a French nobleman, the Comte de Buffon (1707–88). Georges-Louis Leclerc, a rich man, devoted his life to science. He spent part of the year on his estate and the other part in Paris, where he was in charge of the king’s gardens – these were much like a zoo or wildlife park today. Early on, he was a great admirer of Newton and his physics and mathematics, but most of his long life was spent investigating the natural world. His aim was to describe the earth and all the plants and animals on it. All his careful research was collected in a massive work of 127 volumes, called simply Histoire naturelle (‘Natural history’). At that time, ‘history’ also meant ‘description’, and in these books Buffon set out to describe all the animals (and a few plants) that he could get hold of.

Buffon described nearly everything he could about his animals: their anatomy, the way they moved, what they ate, how they reproduced, what uses they were to us, and much else besides. It was a wonderfully modern attempt to see animals in their environment as far as possible. In one volume after another, he examined many of the known mammals, birds, fishes and reptiles. This massive work came out over about forty years, from 1749, and readers eagerly awaited each new volume. They were translated into most European languages.

Buffon was fascinated by all the characteristics of each animal he examined. As he famously said, ‘Nature knows only the individual’, meaning that there was no order in nature, only a lot of individual plants and animals. It was only humans who tried to classify them into groups, for their own use. Of the Great Chain of Being, he said that nature was very full but it could only be studied one creature at a time.

Buffon’s great rival was the Swedish doctor and naturalist, Carl Linnaeus (1707–78). Linnaeus learned medicine but his real passion was plants. He spent most of his life as a professor at the University of Uppsala, in northern Sweden. Here he maintained a botanical garden, and sent many students all over the world to collect plants and animals for him. Some of his students died on their travels, but his followers remained devoted to Linnaeus’s great goal: to name accurately all the things that exist on earth. To help with his naming, Linnaeus classified them, that is, he defined their essential characteristics. This allowed him to place them within the ‘order of nature’. When he was still in his twenties, in 1735, he produced a short book called Systema Naturae (‘The system of nature’). The book was basically a long list of all the known species of plants and animals, grouped by genera. He published twelve editions in his lifetime, each time expanding his list as he learned about more kinds of plants and animals, especially those that his students discovered for him in America, Asia, Africa and other parts of the world.

Since the ancient Greeks, naturalists had asked whether there could be a ‘natural’ classification of the things in the world. Do things have a timeless or God-given relationship to each other?

And if so, how can we find it out? In the Christian era, the most common assumption was that God had created each species of plant and animal ‘in the beginning’, for Adam to name, and that what we see now was the product of time and chance.

Linnaeus was sympathetic to this view, but he realised just how much plants and animals had changed since their creation. This made a ‘natural’ classification very difficult to achieve. So what was needed first, he thought, were some simple rules to order and classify all the things of the world. Second, he wanted to give things a simple label to identify them. This was his life’s task: he saw himself literally as a second Adam, giving things their precise names. After all, how could zoologists or botanists discuss a kind of ‘dog’ or a kind of ‘lily’ unless they knew exactly what kind they were talking about? Nature, Linnaeus thought, had to have pigeonholes, and when everything was in its proper box, then science could be done.

Linnaeus classified just about everything: minerals, diseases, plants and animals. Among the animals, he made a bold move: he included human beings in his scheme. In fact, he gave us the biological name we still have: Homo sapiens, which literally means ‘wise, or knowing, man’. Many naturalists before Linnaeus had confined themselves to what is sometimes called the ‘natural world’, and therefore excluded human beings from their schemes.

Linnaeus, the son of a minister, was deeply religious. As he pointed out, however, there were no biological reasons why human beings were not simply animals, as are dogs and monkeys, and so they needed to be included in his system of nature.

The two most important categories for Linnaeus in his work of taxonomy (the scientific word for classification) were the genus and the species. He always used a capital letter to name the genus (we still do), and a lower-case letter for the species: thus Homo sapiens.

The genus was a group of plants or animals that shared more basic characteristics than species share. For example, there are several different species of cat in the genus Felis, including our domestic cat (Felis catus) and the wildcat (Felis silvestris). (In those days everyone learned Latin in school, so his labelling would have been easy to understand: felis meant ‘cat’, catus ‘cunning’, and silvestris ‘of the woods’.) Linnaeus knew that there were different levels of resemblance or difference between living creatures. At the top of his grand scheme he had three kingdoms: plants, animals and minerals. Under these were classes, such as the vertebrates (animals with spinal cords: donkeys, lizards, and so on); within a class were orders, such as the mammals (creatures that suckle their young); one notch down was the genus; followed by the species. Below species, there were varieties. Within the human species, these varieties were called ‘races’.

Of course, there are individuals – a person, plant or animal with its own peculiar characteristics, such as height, male or female, hair or eye colour, or tone of voice. But you don’t classify individuals as such, rather you put them into a group that you can then classify. Later scientists found they had to add extra ranks into Linnaeus’s original system, such as families, sub-families and tribes. Lions, tigers and domestic cats are now all grouped in the family of cats.

The sum total of all individual plants and animals makes up the living world, and it was this that Buffon referred to when he insisted that this basic category – the individual – was the only certain one.

The really crucial level for Linnaeus was that of the species. He devised a simple system for identifying each plant species, based on the male and female parts of their flowers. It allowed amateur botanists to roam the woods and fields and identify what they were seeing. Even though it was only in plants, Linnaeus’s sexual system disturbed some people and also stimulated a few mildly erotic poems. Most importantly, his classification of plants worked well.

It gave botany a real boost. After Linnaeus’s death, his important plant collections were bought by a wealthy Englishman, who established the Linnean Society of London. It is active to this day, after more than 200 years.

We still use many of the names that Linnaeus introduced to identify plants and animals. One of them was the order of animals that includes human beings, the primates. We share that order with apes, monkeys, lemurs and other animals that share many characteristics with us. Linnaeus did not believe that one species can evolve into another: he believed that God had specially created each separate species of plant and animal. But he realised that human beings were part of nature, and that the rules by which we study the natural world could also be used to understand mankind.

What we mean exactly when we say that this or that group of plants or animals is a biological species continued to puzzle naturalists. It still does. But Linnaeus’s framework was changed a century later, by another naturalist who also loved plants: Charles Darwin.