strange attractor website

A Simple Guide to Evolution

Evolution is a complex process; finding out how it works is rather like trying to complete a complicated jigsaw which has no picture on the box. In the last few hundred years many people have linked together pieces of evidence and produced some startling images, but the jigsaw of evolutionary knowledge is still incomplete. There have always been vigorous arguments about how best to fit the pieces together and even fiercer arguments on how we should interpret and respond to the images that we are shown.

 Sweden and revolutionary France A quick dash from ancient Greece to 18C

The Greek philosopher Aristotle (384 to322 BC) had a theory which explained the variety of life forms: he believed the lowest organisms originated from primeval slime and these simple beings changed into higher and more perfect types. Man was the culmination of this process. Aristotle also attempted to classify living things: his system divided animals into those with red blood and those without, and divided the red blooded creatures into mammals, lizards, birds and fish.

The system of classification we still use today was introduced by Carl Linnaeus (1707 -1778), a Swedish botanist. He used a Latin nomenclature, as was the custom of the time, to classify plants and animals, and gave each species a family name and a species name. He classified plants according to their reproductive organs; at the time some people were rather scandalised by his emphasis on the sexual nature of flowers. Classification is now based on our understanding of the relationships between the species. Linnaeus’s original conviction that species never changed was later modified when he observed that the mating of different species could produced hybrids. The idea of evolution did not occur to him however, and his stance was one of awe at nature allied to a belief in God. It was not until the eighteenth century that the idea that species changed over time and that everything that lived, men, mosquitoes or mushrooms, had the same origin was thoroughly investigated.

The French scientist Lamark (1744 -1789) was responsible for considerable advances in the classification of animals. He was a Professor at the Jardin de Plantes in Paris and worked on worms and insects. He was also the first to think that species evolved over time; to see clearly that there was a jigsaw to be completed. Lamark suggested that the use or disuse of a structure would cause it to increase or decrease in size, and this change could be inherited. The usual example given to illustrate this is the neck of the giraffe, elongated through generations of reaching for leaves near the top of trees.

A glimpse at the enlightenment and utopian ideals

The idea of evolution interested Erasmus Darwin (1731 -1802) who was a physician, poet and the grandfather of Charles Darwin. In his work ‘Zoonomia’ (1794-1796) he speculated that all life had arisen from single living filament. Erasmus Darwin was a Unitarian and adherent of the views of the Enlightenment.  Unitarians believed in God and in the teaching of Jesus, but did not accept the doctrine of the Trinity as taught as an article of faith by the established Church of England. The enlightenment, a philosophical movement which believed that human reasoning was to be preferred to unquestioning faith, was associated with 'scientific' thinking and often at odds with the religious establishment of the time.

A clergyman and political economist called Thomas Malthus (1766 – 1834) had a profound influence on evolutionary thought. He wrote An Essay on the Principles of Population in 1798 as a response to his father’s attempt to convert him to the ideas of William Godwin and the Marquis de Concordet. They believed in the perfectibility of human society, and assumed that humans would naturally progress towards a utopian society. Concordet was actively involved in the French Revolution (1788 – 1799) and Godwin was also much influenced by the heady ideals of the time. Thomas Malthus thought that the utopian ideals of a society in which equality, wealth, happiness and virtue naturally flourished were incompatible with the facts of human existence, which he pointed out was regulated by the same laws as the existence of other animals. He noted that humans had the potential to reproduce so as to double their numbers every 25 years, as had happened in the newly colonised America. He thought that it was unlikely that any land could provide food for this potential increase in population indefinitely. He also considered the reasons why this potential increase in population did not normally occur, and pointed out that many of the reasons he listed: war, famine, infanticide, and late marriage resulted in misery and vice. His views were hotly debated at the time, and have been very influential since. Darwin and Wallace were stimulated by his work to consider the mechanisms that regulated animal and plant populations; Marx and Engels rejected his ideas, as Malthus had rejected the ideas held by earlier social revolutionaries.

The young Darwin builds on Lyell's geological foundations

Charles Darwin (1809 - 1882) is the best known evolutionist of all time. He studied classics at Cambridge, and at that time a book by William Paley (1743 -1805), ‘A View of the Evidence of Christianity’ was required reading. Paley’s other famous book ‘Natural Theology: or, Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature’ (1802) introduced the idea that the existence of God could be inferred from nature: just as anyone would infer from finding a watch that it had been made by a watch-maker, so anyone examining the wonderful array of plants and animals on earth could safely infer the existence of a creator. Darwin was very taken by William Paley’s work, and when he set off on his voyage around the world on HMS Beagle after he graduated, Charles may well have been a more orthodox Christian than his free-thinking grandfather Erasmus Darwin.

Charles took on the Beagle the first volume of ‘Principles of Geology’ by Charles Lyell (1797 -1875). Lyell revolutionised ideas on geology. It had been thought that the surface of the earth had been moulded by a few past catastrophes like Noah’s flood, but that this period of upheaval was over, but Lyell found evidence that change was continuous over vast periods of time. Darwin demonstrated that the earth was still changing when he measured an eight foot uplift in the land after an earthquake in South America. Lyell taught that "the present is the key to the past", but he did not apply his theories of continual change to the species that lived on the ever changing earth, it was left to his younger friend Darwin to do this.

In South America Darwin found the fossils of extinct creatures and noted their resemblance to current species. He noted that the variety of birds and animals found on the Galapagos Islands differed from those on the mainland and that tortoises and finches were different on each of the islands. He proposed a mechanism by which species changed over time and devoted many years to finding evidence for it. He called this mechanism Natural Selection, and explained that as many of the offspring of all species did not live long enough to breed, those that were the best adapted, or fittest, would survive in that particular time and situation and pass on their characteristics to the next generation.  Each generation would therefore be subtly different from the last and varieties would arise, just as varieties of pigeons, cats and dogs arise from the selections made by breeders. Eventually these varieties would come to be so different that they would become separate species. He used the analogy of a tree of life, where everything was descended from a single ancestor, which formed the tree trunk, extinct species formed the branches, and current species were at the end of the twigs. Darwin fitted a number of jigsaw pieces together; William Paley’s ideas didn’t fit, which made Darwin uncomfortable for a while because it meant that his ideas did not accord with the conventional religious beliefs of the time.

Evolution and Continental Drift - Wallace and Wegener

Alfred Russel Wallace, (1823 –1913) traveller and collector of natural history specimens, thought, as Darwin did, that natural selection was the main engine of evolution, and that geographical separation, as on islands, often favoured the evolution of species. He  noticed that in some southern Indonesian islands the mammals were marsupials, as in Australia, above a line he mapped out, (now called Wallace’s Line) the animals were similar those found in Asia. The reason for this was not understood until the ideas of Alfred Wegener (1880 -1930) were accepted.  He was a German meteorologist and climatologist who deduced from the evidence of fossils that the continents had all been joined in one land mass which he called Pangea, and that this mass had broken up and the continents we know today drifted over the surface of the planet. Wallace’s line marks the junction between the Asian and Australian continents, which had been further apart in earlier epochs. Wegener’s theory was controversial until researches in the 1960s showed that the solid continents did indeed float on a fluid layer.

Darwin's followers and Victorian philosophies

Darwin thought of man, like all other species alive then, as situated at the end of a twig of the evolutionary tree of life, but the philosopher Herbert Spencer (1880-1903) believed that man was at the top of the tree: the culmination of the evolutionary process. He and others were so taken by Darwin’s insights that they decided that evolution shaped society as well as species, and that society could assist the process of perfecting mankind by allowing the strongest to dominate the weak. The message of ‘survival of the fittest’, a term coined by Herbert Spencer, seemed to fit this era of industrialisation and colonisation. The followers of Darwin took off in various directions, some using it to justify appalling practices such as eugenics and the refusal to help the poor. They responded to Darwin's work as though his view was a complete picture when in fact, as Darwin realised, they were looking at a half-completed jigsaw. Darwin remarked that he was unable to prevent people taking his work further than he considered safe.

Mendel the monk to modern genetics

At the time no one knew anything about the mechanisms through which species passed on characteristics to the next generation. They have proved to be complex. A German monk, Gregor Mendel (1822 -1884) began to put together this section of the jigsaw with researches in which he crossed wrinkled and smooth coated peas. In the early 1900s scientists found bodies called chromosomes in the nucleus of living cells, and saw that they split when the cell divided. They found that each sperm or egg cell contains a split chromosome, and the two halves unite to make a new nucleus.  Genes contain instructions on how to shape the new organism, and in 1953 Crick, Watson and Franklin discovered that genetic material or DNA had a spiral structure, a double helix, which unzipped when the cell divided. Since then the structure of many genes has been worked out. It has proved more complex than was originally thought to work out exactly how genes will affect the organism. Some, like Mendel’s genes in peas, have easily recognisable effects that are inherited in predictable patterns, but some will only show their effects in certain environmental conditions, or if other genes are present. Knowing the genetic structure of an organism helps scientists to understand its evolutionary origin, and this understanding has modified ideas on the relationships in the evolutionary tree. Genomics is the science that is seeking to understand these processes; it is advancing rapidly, adding more questions to be answered as new knowledge adds to our understanding of the complexity of the relationships between organisms. The human genome has been sequenced; the worm genome is being investigated with a view to understanding the effects of these important organisms on pollution in the soil. Genetic engineering has potential in many areas, one example is harnessing the strength and elasticity of spider silk. It has recently been found that genetic material is not only inherited, but can cross the species boundary. This threatens to uproot the idea of the tree of life, and leave in its place a tangled web.

Co-operation and Evolution - Symbiosis and Niche Construction

In Darwin’s time competition between individuals and species appeared to be the main driver of evolution, but in 1970 Lynn Margulis uncovered a different aspect of the jigsaw in her book The Origin of Eukaryotic Cells.  Apart from viruses and bacteria all living cells are eukaryotic, that is, they have a nucleus. In addition to chromosomes the nucleus contains mitochondria, which generate energy for the cell, and plant nuclei also contain chloroplasts, which capture energy from the sun. Mitochondria and chloroplasts look like bacteria, and Margulis produced evidence that this was their origin. Her theory, now accepted, is that the first cells with a nucleus were combinations of different single celled organisms, that is, two or three cells in one envelope which lived in symbiosis, a union which benefits all partners. These new symbiotic cells had advantages that enabled them to develop into the vast array of multi-celled organisms we see today. Margulis demonstrated that co-operation enabled evolution to take a monumental leap forward.

There are many other instances of symbiotic behaviour, lichens, for instance, are composed of fungus and algae living together in one body. Many insects, bees and ants for instance, succeed by living co-operatively in colonies. The strategy of forming flocks or swarms also has benefits for birds and animals, for instance migrating caribou and mating horseshoe crabs. Evolutionary understanding has been given another dimension by work on ‘niche construction’ by Odling-Smee, Laland and Feldman. They point out that living organisms not only fit into a niche, but also construct their own niches, nests, termite mounds etc, and that this modification of the environment also alters the evolutionary dynamic.

Evolution and Religion

The social Darwinists' partial and controversial take on evolution took hold in late 19C, particularly in the USA. It's exponents advocated a social programme that lacked humanity, so it was understandable that religion became the refuge of those appalled by their views.  Evolution, however, does not prove that we should breed a master race or abandon the poor and weak; it does not prove there is no God; it simply explains how the various forms of life developed on this planet. A person who believes that the creation story in Genesis is the literal truth rather than a mythical explanation of the diversity of life could not accept the truth of evolution, but in my view, evolution is not incompatible with a belief in God. Evolution does not attempt to explain how the solar system and the rest of the universe came into being, or to answer the question as to whether a force lies behind the universe, or, if there is nothing behind the universe, why anything rather than nothing exists. Through the ages, religious people of all faiths have affirmed the essential mystery of the nature of God; evolutionary theory simply makes it difficult to take refuge in spiritual certainty. A true realisation of the complexities of evolution also makes it unreasonable to issue dogmatic statements on the human situation. There is more discussion on the impact of evolution on religion in Evolution and Religion .

Debates and developments in recent evolutionary science

In the past people have thought of evolution as a provisional theory because evolution is too slow to be observed, but patient field studies have shown examples of organisms evolving in the short term, for instance, mussels in the eastern US and  finches in the Galapagos.

In the early 1900's scientists believed that the effect of natural selection had been overstated and that mutation was more important. Arguments have raged as to whether evolution proceeds steadily or has periods of intense activity, dubbed 'punctuated equilibrium' by Stephen Jay Gould.  Scientists have become over-excited by their own work and made unreasonable claims: possibilities are treated as certainties, ‘breakthroughs’ announced in a great buzz only to come to a crushing dead end. Evolutionary psychology, which seeks to explain behaviour by reference to ancient evolutionary pressures is a controversial expansion of evolutionary theory; and given that our knowledge of the pressures exerted on early hominids and  and our understanding of human psychology are incomplete, any conclusion reached by evolutionary psychologists needs to be carefully evaluated.

Working out the relationships between species and the complex mechanisms of evolution has been a story of fervent human curiosity and of the wish to understand the world as it really is, but sometimes the wish to know the truth has strained against the wish to believe in what is desired; some scientists have even convinced themselves that theirs is the only way of seeing the world. Arguments which should be logical and evidence-based become acrimonious and personal, generating clouds of steam but no light. Science is influenced by the values of society as all science has to be funded by society, and scientific understanding influences contemporary philosophy and sociology. Our knowledge of evolution is continually being enriched with new ideas and evidence and our understanding is constantly changing.

Responding to current knowledge of evolution and genetics

The proper interpretation and response to the new pictures on the jigsaw will be debated by those with an interest in promoting theories of government, religion and environmental concerns. The way that our society reacts to modern evolutionary ideas, for instance, in the way we use genetics, or how we act now that we begin to understand the web of connections between all living things will depend on which messages are chosen out of the complexity on offer. ‘Survival of the Fittest’ is the slogan that most people think of when evolution is mentioned, often with distaste as it is connected with ideas of domination and eugenics, but other, equally true, but very different, slogans could be invented: ‘Symbiosis is Success’ for instance: co-operation for mutual benefit was a powerful force in the momentous changes of evolution, and has also been a powerful force in civilisation. It is as though conflict and co-operation are two sides of the same coin, or, to continue the jigsaw analogy, as though pictures have been painted on both sides of the jigsaw. It could also be argued that the mechanisms of evolutions are so complex that the puzzle of evolution is more like a Rubik’s cube, a three dimensional puzzle involving interactions between the organism, its genetic inheritance, the physical environment and other living organisms.

I hope that this short article on a complex subject will encourage people to think about and take part in the debates on evolution and genetics. While scientists carry on carefully fitting together pieces in the ever expanding jigsaw and showing us new and dazzling images, and philosophers think of new ways in which the images can be interpreted,  everyone should be prepared to think about how to take the best way forward in their light. Human instincts, feelings, ethics and judgement should be applied to the results of scientific evidence, understanding always that the complete picture of evolution and the tangled interaction between species lies beyond our vision.

You may  print any work by Anne Bryan on this or any other page of the web site for your own use or to pass on to a friend, and you may also quote Anne's work in assignments as long as the source is acknowledged. Please don't copy anything from this web site into magazines, newsletters or other web sites without permission or acknowledgement.  Ask for permission by E mail  

Back to Strange Attractor homepage

Darwin biography, as impartial as I can make it, without  fundamentalist 'religious' disapproval or overzealous 'scientific' trumpeting of his work.

A Simple Guide to Evolution - a short history of evolutionary ideas
Evolution and Religion a discussion of the impact of evolution on religion
'Unsung by Singers'  considers the scarcity of poems on science.
'Space with Wordsworth'  explores the idea that science is hostile to poetry.
A Flash of Golden Fire considers the love of nature with reference to a poem by Coleridge, travel writing by the explorer Mungo Park and a sci-fi novel by Philip K Dick.