Sunday, 21 June 2009

Paradigm shift

The concept that there is such a thing as prehistory, an era undocumented by written records, is actually quite recent. In 1650 James Ussher, Anglican Archbishop of Armagh, famously calculated from Biblical texts that the Earth had been created in 4004 BC. In 18th Century Europe, when Carl Linnaeus coined the term Homo sapiens, this date was still widely accepted. Most believed that the earliest part of human history was fully recorded in the texts of ancient Greek and Roman historians and in the Old Testament itself. The Abrahamic religions held that Earth and time were created simultaneously and that it was therefore meaningless to speak of earlier times, because time itself did not exist. Even to ask what God had been doing before He created the world was considered poor form and the religious reformer John Calvin said that the answer should have been “making Hell for the curious” (the remark is often erroneously attributed to St. Augustine).

In astronomy, the work of Copernicus, Kepler, Galileo and Newton eventually relegated the Earth from the centre of the Universe to the 3rd rock from the Sun; humanity’s demotion from somewhere “a little lower than the angels” to what the American biologist and author Jared Diamond has described as “just another species of big mammal” required a paradigm shift of equal proportions.

Like Galileo, many of the early workers in the field were flying in the face of religious orthodoxy, though this was not always the case and indeed Linnaeus, who was responsible for formally assigning humans a place in the animal kingdom alongside apes and monkeys, went out of his way to fit his work into God’s scheme of things. In fact the study and classification of the natural world was always considered a perfectly respectable pursuit, one that went back to Classical times. Such studies, with a view to achieving a better understanding of the works of God, were known as natural theology.

The first attempt at a systematic classification of the natural world was made by Aristotle, who believed that everything in the universe had its place in a Great Chain of Being or Scala Naturae (“Ladder of Nature”), being ranked from the lowest to the highest. The hierarchy began with God at the top, followed by angels, then kings, princes, and so on through to ordinary people, animals, plants, minerals etc.

Within this chain, Aristotle divided the various species of living organisms into two groups – animals and plants. Animals were further divided into three categories - those living on land, those living in the water and those living in the air, and were in addition categorised by whether or not they had blood (broadly speaking, those “without blood” would now be classed as invertebrates, or animals without a backbone). Plants were categorised by differences in their stems.

Aristotle’s system remained in use for hundreds of years but by the 16th Century, knowledge of the natural world had reached a point where it was becoming inadequate. Many attempts were made to devise a better system, but it was not until 1735 that the Swedish biologist Carl Linnaeus published the first edition of Systema Natura (“System of Nature”), in which he proposed a hierarchical classification of the natural world, dividing it into the animal, plant and mineral kingdoms. Each kingdom was further subdivided by class, order, genus and finally species. Species were arranged within the higher groupings on the basis of physical similarities, each grouping being named on the basis of a defining feature. In addition, Linnaeus adopted the system of binomial nomenclature first proposed over a century earlier by Gaspard Bauhin, under which a species is assigned a generic name and a specific name. The generic name refers to the genus and the specific name represents the species itself.

Within the Linnaean system, the Mammalia (mammals) are the class of animals that suckle their young. It is said that Linnaeus adopted this aspect as the defining feature of the group because of his strongly-held view that all mothers should breast feed their babies. He was strongly opposed to the then-common practice of “wet nursing” and in this respect he was considerably ahead of his time.

The mammals were divided into eight orders, including the Primates; these in turn were divided into two genera: the Simia (monkeys, apes, etc) and Homo (man), the latter containing a single species, sapiens – hence Homo sapiens, meaning (some would say ironically) “wise man”.

As originally conceived, the Linnaean system did not accord equal status to apparently equal divisions; thus the Mineral Kingdom was ranked below the Plant Kingdom; which in turn sat below the Animal Kingdom. Similarly the classes were assigned ranks with mammals ranking the highest and Insecta (insects) and Vermes (worms) the lowest. Within the mammals the Primates received top billing, with Homo sapiens assigned to pole position therein.

This hierarchy within a hierarchy reflected Linnaeus’ belief that his system reflected Aristotle’s Chain of Being, with Mankind at the top. Indeed the term “primate” survives to this day as a legacy of that view. Never the most modest of men, Linnaeus claimed that “God creates, Linnaeus arranges”.

Linnaeus’ classification system, as set out in the 10th edition of Systema Naturae, published in 1758, is still is considered the foundation of modern taxonomy and it has been modified only slightly in that we now regard all equivalent divisions as being equal.

The Linnean Taxonomy shows us where humans fit into the grand scheme of things, but it has nothing to tell us about how we got there. Linnaeus did not believe that species changed. His thinking was still firmly rooted in that of Plato, who believed that every type of object in the universe was represented by an immutable Form, from which all instances of that object were derived; thus for example all cats were derived from the Form of a Cat. Plato’s Theory of Forms explicitly rejected evolution: the Form of one species of animal could never evolve into that of another.

Others, though, were already beginning to question this view. The existence of extinct organisms in the fossil record represented a serious problem for creationism. Fossils had been known for centuries and it was becoming clear that they represented in many cases life forms that no longer existed. The English canal engineer William Smith and French naturalist Georges Cuvier were among those who recognised that rocks of different ages preserved different assemblages of fossils, implying a sequence of events more complex than could be accounted for by the Biblical account of a single great flood.

In 1796 Cuvier put forward a possible solution known as catastrophism, which was a modified form of creationism. He proposed that extinctions had been caused by periodic catastrophes, of which Noah’s flood was the most recent and the only one where humans had been present. New species replaced those that had been wiped out, created ex nihil by God. No species contemporary with humans had ever become extinct, as breeding populations of all of these had been taken aboard the Ark.

However the creationists were by now on increasingly shaky ground. In 1797 a man named John Frere presented evidence suggesting that humans had been contemporary with now-extinct animals. He had been contemplating the problem of what we now recognise as tools from the Stone Age. These artefacts had been known for centuries but – in the absence of any concept of prehistory – they were not thought to be of human origin and were thought to be thunderbolts or the work of elves.

Frere wrote to the Society of Antiquaries of London submitting some flint artefacts found at Hoxne, Suffolk. These had been found twelve feet below the ground and were associated with bones of extinct animals. Frere suggested that the artefacts were “weapons of war, fabricated and used by a people who had not the use of metals. The situation in which these weapons were found may tempt us to refer them to a very remote period indeed, even beyond that of the present world.”

Even before Curvier published his theory, the Scottish geologist James Hutton was formulating the principles of what later became known as uniformitarianism. Hutton’s Investigation of the Principles of Knowledge was published in 1794 and The Theory of the Earth the following year. Hutton argued that geological principles do not change with time and have remained the same throughout Earth’s history. Changes in the Earth’s geology occurred gradually and were driven by volcanic action rather than floods and other biblical catastrophes. It was clear that the Earth must be much older than 6,000 years for these changes to have occurred.

Unfortunately, Hutton’s writing style was so obscure that his books attracted little attention in his lifetime. Not until the 1830s did his theories did not gain widespread acceptance, when they were popularised by fellow Scot Sir Charles Lyell. Lyell, who also coined the word “Uniformitarianism”, published Principles of Geology between 1830 and 1833.

In the meantime, the evidence for the antiquity of mankind was growing. In 1813 the Danish historian Vedel Simonsen suggested that the weapons and implements of the earliest inhabitants of Scandinavia had first been made of stone, then of bronze and finally of iron. Then, in 1816 Christian J├╝rgensen Thomsen became the first curator of the Danish National Museum of Antiquities in 1816. His first task was to classify artefacts in the collection and to put them in some semblance of order.

Thomsen hit on the idea of classifying them on the basis of the material from which they were made and followed Simonsen’s suggestion that the iron artefacts must be more recent than those made from bronze, which in turn must be more recent than those of stone. Thus was born the Three Age System, whereby the pre-literate past was divided into the now familiar Stone, Bronze and Iron Ages. A guidebook to the museum was translated into English in 1846, after which the Three Age system was widely adopted.

A year later, a French customs official named Jacques Boucher de Perthes published his conclusions regarding the stone implements that he had collected some years earlier from gravel pits in the Somme valley. The implements were clearly of human manufacture and associated with the remains of extinct animals, again suggesting that humans and now-extinct animals had once co-existed.

In 1859 the geologist Sir Joseph Prestwich and archaeologist John Evans visited Boucher de Perthes in France. They were convinced by his findings and on returning to Britain gave a series of presentations to the Royal Society, the Society of Antiquaries and the Royal Institution in London. What they termed the Antiquity of Man was widely accepted, finally confirming that the human past extended back way beyond the reach of the earliest written records. This was a landmark moment in the acceptance of prehistory as a valid concept, but it was largely overshadowed by another pivotal event in our understanding of humanity’s origins: 1859 also saw the publication of Charles Darwin’s On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (usually simply referred to as The Origin of Species).

The son of a wealthy doctor, Darwin was born in 1809. An unwilling medical student, he studied at Edinburgh and Cambridge before being appointed Naturalist and gentleman companion to Captain Robert Fitzroy of the barque HMS Beagle, joining the ship on her second voyage. Darwin sailed round the world in the Beagle between 1831 and 1836. He studied finches and turtles on the Galapagos Islands – he found different turtles had originated from one type, but had adapted to life on different islands in different ways.

Darwin developed the theory of natural selection between 1844 and 1858. The theory was as the same time being independently developed by Alfred Russel Wallace and in 1858 Darwin presented The Origin of Species by means of Natural Selection to the Linnaean Society of London, jointly with Wallace’s paper. Wallace’s independent endorsement of Darwin’s work leant much weight to it. Happily, there were none of the unseemly squabbles over priority that has bedevilled so many joint discoveries down the centuries. The Origin of Species was published the following year and promptly sold out.

The theory of evolution by natural selection is based on four assumptions. Firstly, all organisms reproduce; secondly there has to be a mode of inheritance whereby parents transmit characteristics to offspring; thirdly, there has to be variation in a population, i.e. the individuals in it will all differ slightly from each other; and fourthly there must be competition for limited resources.

The differences between individuals in a population mean that some might be able to compete more effectively than others. These ones are more likely to go on to reproduce and transmit their advantageous traits to their offspring, which in turn would be more likely to reproduce themselves. Adaptive or advantageous traits are characteristics that help an individual survive, e.g. an elephant’s trunk, which enables it to forage in trees, eat grass, etc; colour vision helps animals to identify particular fruits, etc; bright distinctive colour schemes are plants’ adaptations to help them to be located. Eventually, a species might become so changed by the accumulation of adaptive traits within its ranks that it could be considered to have evolved into a new species.

The mechanism by which these traits are transmitted was unknown in Darwin’s time; not for another century would the role of DNA as the “molecule of inheritance” be confirmed.

Darwin hinted that his theory might throw light on human origins, but it was not until his second work The Descent of Man and Selection in Relation to Sex, published in 1871, that he proposed that humans had evolved from apes. This was a number of years after his friend and advocate Thomas Henry Huxley had put forward the idea in Evidence as to Man’s place in Nature, published in 1863. Darwin was characterised as “the monkey man” and caricatured as having a monkey’s body. But after his death in 1882, he was given a state funeral and is buried in Westminster Abbey near Sir Isaac Newton. An admittedly-dubious BBC poll ranked Charles Darwin as the 4th greatest Briton of all time, behind Sir Winston Churchill, Isambard Kingdom Brunel and (inevitably) Princess Diana, but ahead of Shakespeare, Newton and David Beckham.

The transformation of mankind’s view of itself was complete: from chosen beings created in 4004 BC in God’s image, to a primate species which had evolved from apes at some unknown time in the distant past. The questions, of course, had barely begun.

© Christopher Seddon 2009

2 comments:

Zuri said...

The Galapagos Islands are the most incredible living museum of evolutionary changes, with a huge variety of exotic species (birds, land animals, plants) and landscapes not seen anywhere else.

Zuri said...

The Galapagos Islands are the most incredible living museum of evolutionary changes, with a huge variety of exotic species (birds, land animals, plants) and landscapes not seen anywhere else.