The theory of evolution: 150 years afterwards

We are coming up to the 200th anniversary of the birth of Charles Darwin in 1809, and the publication of On The Origin of Species. 50 years later. I hardly dare venture into a field where so much has been written and said about Darwin and Darwinism since then, and I am surrounded by microbiologists who know far more than I do. But I will do my sketchy best.

The publication of the theory of evolution by natural selection marks a fundamental shift in human thinking, one of the most important in our intellectual history. Such shifts take place rarely, but with the advance of science they are now becoming more frequent.

A good example is the period preceding the publication of Darwin's great book On the Origin of Species. Until the 18th century few had challenged the timescale of Earth history set out in the Book of Genesis. Gradually this came under challenge, not least from Cuvier and Lamarck, but it was James Hutton who first described in detail the immensity of Earth history in which he saw no "vestige of a beginning" and "no prospect of an end". Then came Charles Lyell's great work in the 1830s, and gradual acceptance of deep time with what it implied. Nonetheless resistance continued. As T. H. Huxley once said, the path of geological speculation was long blocked by a thorny barrier carrying the notice: "No Thoroughfare. By Order of Moses".

More recently we have seen the fundamental shift in thinking caused by the movement of tectonic plates. Again this was fiercely resisted, and Alfred Wegener, who first identified plate movement, died before his ideas were generally accepted. Another more recent example is the introduction of Gaia theory, or Earth Systems Science, which describes, in the words of James Lovelock and Lynn Margulis in 1984: "the evolution of a tightly coupled system whose constituents are the biota and their natural environment, which comprises the atmosphere, the oceans and the surface rocks". I shall have more to say on this later.

Unfortunately unfamiliar ways of looking at the familiar, or any rearrangement of the intellectual furniture, tend to arouse indignation far beyond rational argument. Academics are as guilty of this as anyone else. Partly this is because most of us are better at looking at the constituent elements of problems than in seeing the connexions between them and understanding how the resulting system works. The theory of evolution is a prime example.

Naturally Darwin himself inherited the mindset of his age, and this is evident in the work which led to the publication of The Voyage of The Beagle. He was influenced by his grandfather Erasmus Darwin and of course by Thomas Malthus, who in 1803 set out the principle that population growth would sooner or later outstrip the growth of resources, with the eventual result of overpopulation and insufficient supply. On his return from his expedition on the Beagle, Darwin had the time and financial independence to pursue his researches as he so wished.

He may conceivably have been influenced by Robert Chambers's anonymous work of 1844 in which Chambers proposed a universal law of development not unlike the eventual theory of evolution by natural selection. The trouble was that Chambers's book The Vestiges of the Natural History of Creation contained bad things as well as good ones, and although widely read was scarcely regarded as serious scholarship. For his part Darwin was aware from the beginning that his ideas about evolution would be highly controversial, and he undertook a programme of detailed work on barnacles, climbing plants, beetles, and in the end worms, to establish his thesis beyond reasonable criticism. When he eventually produced On the Origin of Species, he admitted that it was like committing murder.

As we know, he was precipitated into publication because Alfred Russel Wallace had come up with similar ideas, and had written to Darwin in 1856 to explain some of his thinking. In February 1858 Wallace completed his work on the subject, and sent a letter to Darwin to elaborate them. Hence the meeting at the Linnean Society in London in July that year when Darwin's and Wallace's papers were first made public. No one took any notice. On the Origin of Species followed the following year, and thereby changed the direction of human thinking about life on Earth.

Looking back over the last 150 years it seems almost extraordinary how much Darwin (and Wallace in some respects) got right. There was:

• the theory of natural selection itself;
• the notion that however diversified species might become over thousands or millions of years, they came from a single stock or tree;
• recognition of selective extinction of species in different circumstances, thereby showing living organisms as a patchwork of possible forms;
• the need for deep time in which evolution could take place (although how much deep time remained a matter of controversy);
• the dispersal of species related to their geographical circumstances (later well illustrated by plate tectonics);
• the role of sexual selection to cause differentiation between the sexes;
• recognition of the co-evolution of species and what Darwin called "the economy of nature" or the biological processes we now describe as ecology;
• finally, the gradual evolution of living organisms similar to the gradual character of geological change over time.

In all this the role of an interventionist and capricious God in creating species from time to time, and of course maintaining them, was unnecessary. When the early geologists found such species as marine reptile fossils, the conventional wisdom then was that if only they looked hard enough they would find them alive somewhere else on Earth.

There was a lot that Darwin did not and could not know. But what has been learnt since, in particular about the mechanisms of mutation and genetic inheritance arising from the work of Mendel and his successors, fits amazingly well with Darwin's original thesis. Thus the discovery of DNA and the identification of the human genome, and now the discovery of jumping genes, or transposons, between very different species.

There has also been modification of Darwin's ideas about selection by bringing in cooperation between species, and what has been called symbiogenesis (or the evolutionary effects of mutual dependence between organisms). Then there are the vagaries of evolution. How organic structures which evolve for one purpose evolve into another: for example how gills for fish eventually become bones for the human ear. All this enriches the theory of evolution rather than qualifies it. Darwin was truly an extraordinary pioneer, and every word he wrote has lasting value. As T. H. Huxley once said: how stupid it was of him not to have thought of the idea himself.

There was particular opposition to Darwin's conception of deep time. Although biblical chronology was easily abandoned by many people, the age of the Earth remained a matter of high controversy. Both Darwin and Huxley needed more time for evolution to take place than many would allow them, notably Lord Kelvin (one of the scientific sages of his epoch). By the time that Darwin died in 1882 and Huxley in 1895, the conventional view remained that the cooling of the Earth did not permit an age of more than 100 million years. Indeed Kelvin maintained that it was closer to 24 million years.

It was not until the discovery of radio activity by Pierre Curie and Albert Laborde in 1903, and its application to the age of the Earth by Ernest Rutherford in 1904, that the immensity of deep time could be recognized. Work on it has of course continued since then, and the age of the Earth is now roughly estimated at 4.6 billion years. The timing of the beginning of life is still in controversy, but probably came around a billion years later.

There was also argument about the gradual character of change, as outlined by Lyell and his successors. Uniformitarianism battled against catastrophism, and generally uniformitarianism won. The truth lies between them. Recently it was Stephen Jay Gould who introduced the idea of punctuated equilibrium in which gradual change could be punctuated by episodes in which evolution of species moved rapidly in response to a variety of ecological circumstances.

Then there was controversy about the alleged contradiction between the second law of thermodynamics and entropy on one side, and the increasing complexity and elaboration of species on the other. Once it had been accepted that the second law of thermodynamics only operated within closed systems and that entropy carried the implication of dispersal rather than disappearance of energy, this objection, if it was ever serious, lost its force.

Last there are still some who reject evolution in any form for religious and related reasons. A poll showing public acceptance of evolution in some 34 countries in 2005 showed that in Europe, Japan and most other industrial countries acceptance was over 60%, whereas in the United States it was only 40% and in Turkey less than 30%. Even the public acceptance of evolution by Pope John Paul II in 1996 has not changed those in evangelical communities who cling to sorts of creationism, including its modern variation intelligent design. It is hard for most Europeans to believe this, but the debate still continues, and if anything has become more acrid. Apparently a few Americans even believe that Joan of Arc was the wife of Noah.

An essential element in Darwin's theory of evolution is the enduring character of change. This goes back to Heraclitus and the early Greek philosophers. Just as the environment changes, so do living organisms and the relationships between them. This brings me to a few words about Gaia theory which in many ways supplements our understanding of evolution.

As was well said in a Declaration at a Conference of the four great International Global Research Programmes at Amsterdam in July 2001:

"The Earth system behaves as a single, self-regulating system, comprised of physical, chemical, biological and human components. The interactions and feedbacks between the component parts are complex and exhibit multi-scale temporal and spatial variability."

As was also said in the Declaration,

"The nature of changes now occurring simultaneously in the Earth system, their magnitudes and rates of change are unprecedented. The Earth is currently operating in a no-analogue state."

It was, I think, Lynn Margulis who described Gaia - or the living Earth - as "a tough bitch". So she is. Over 3.6 billion years, it is her robustness which is so impressive and reassuring. She has survived the great extinctions from outside the Earth, and the great catastrophes from within it. This has required a remarkable resilience whereby physical and biological mechanisms have adapted to new circumstances.

Gaia is a lady who has remained broadly the same underneath, but can wear many clothes for many weathers and many fashions. She has no particular tenderness for humans. We are no more than a small, be it immodest, part of her. Only in the last tick of the clock of geological time did humans make their appearance, and only in the last fraction of it did they make any impact on the Earth system as a whole.

Only now do we know how vulnerable our little planet is to human depredations. A periodical visitor from outer space would find more change in the last 200 years than in the preceding 2000, and more change in the last 20 years than in the preceding 200. The association between humans and their environment, including the micro-world in and around them, has changed at every change of human evolution: from vegetarians to meat eaters, from hunter gatherers to farmers, and from country to city dwellers. But the most radical divide was the beginning of the industrial revolution in Britain some 250 years ago. Before then the effects of human activity were local, or at worse regional, rather than global. Now they are indeed global.

All the civilizations of the past cleared land for cultivation, introduced plants and animals from elsewhere, and caused a variety of changes, thus pushing evolution in different directions. The southern and eastern coasts of the Mediterranean are a case in point. The soils have now become sand, the trees are often camel grass, animals of all kinds have disappeared, and the clouds sail overhead to drop their rain somewhere else. It may be hard to believe as the storms hit Catalunya but if some climatic predictions are correct, the northern coasts of the Mediterranean, including Catalunya, may one day suffer the same fate.

The human impact on the Earth, and thus the future evolution of life, falls into five categories, all interlinked. First there has been a giddy-making increase in human numbers, rising from around 1 billion at the time of Malthus at the end of the 18th century, to over 2 billion in 1930, and now close to 7 billion. The world population is increasing by over 80 million people every year. More than half of them now live in cities, which are themselves like organisms drawing in resources and emitting wastes. In short we are spreading like dandelions, or any other species on a bonanza. Indeed it has been suggested that human multiplication is a case of malignant maladaptation in which a species, like infected tissue in an organism, multiplies out of control, affecting everything else.

All this has profoundly affected the condition of the land surface and the organisms that live on it. More humans need more space and more resources. Soil degradation is widespread, and deserts are advancing. Such degradation is currently estimated to affect some 10% of the world's current agricultural area. Although more and more land, whatever its quality, is used for human purposes, increase in food supplies has not kept pace with increasing population. Application of bio-technology, itself with some dubious aspects, can never hope to meet likely shortfalls.

In the meantime industrial contamination of various kinds has greatly increased. To run our complex societies, we need copious amounts of energy, at present overwhelmingly derived from dwindling resources of fossil fuels laid down hundreds of millions of years ago. We also have to deal with the mounting problems of waste disposal, including the toxic products of industry.

Next there has been increasing pollution of water, both fresh and salt. No resource is in greater demand than fresh water. At present such demand doubles every 21 years, and seems to be accelerating.

Then there have been changes in the chemistry of the atmosphere. Acidification from industry has affected wide areas of both land and sea. Greenhouse gases are increasing at a rate which is already changing average world temperature, with big resulting variations in climate and local weather as well as sea levels. Carbon levels in the atmosphere are now the highest in the last 650,000 years, and rising all the time. We face not only climate change but climate destabilization.

Lastly humans are causing extinctions of other organisms at many times the normal rate. Indeed the rate of extinction is reminiscent of what happened when the dinosaurs came to an end some 65 million years ago. Yet we remain ignorant of our own ignorance. The rising damage to the natural services on which we, like all species, depend is immeasurable. There is no conceivable substitute for such services. At present there is a creeping impoverishment of the biosphere.

Then what about the effects on humans themselves? How much is human nature or behaviour a product of evolutionary change or of the learned environment? I remember the debates of the 1970s on sociobiology, and the passions they aroused. At the end I concluded that there was much that we inherited, and much that we learned. Consciousness remains an elusive concept throughout, but must have evolved to what we know today.

So what does all this mean for evolution in general? In his book The Meaning of the 21st Century James Martin has distinguished what he has described as primary, secondary and tertiary evolution. He suggests that:

"Primary evolution is the mutation and natural selection of species - a glacially slow process ...

Secondary evolution refers to an intelligent species learning how to create its own form of evolution. It invents an artificial world of machines, chemical plants, software, computer networks, transport, manufacturing processes and so on. It learns how to manipulate DNA ...

Tertiary evolution refers to something which is just beginning on Earth. An intelligent species learns to automate evolution itself."

The idea of automated evolution needs some explanation. In a phrase it represents a vast acceleration of change. James Martin writes that with the machines we envisage today, it could be a billion times faster.

"Furthermore it will be incomparably more efficient. Darwinian evolution is described as being random, purposeless, dumb and Godless. Automated evolution is targeted, purposeful, intelligent, and has humans directing it and changing its fitness functions on the basis of results. In Darwinian evolution, the algorithm stays the same. In automated evolution evolution researchers will be constantly looking for better techniques and better theory. The techniques of evolvability will themselves evolve."

The applications of human technology already range beyond enumeration. Already chips have been inserted into humans for a variety of purposes. In his 1898 fantasy The Time Machine, H. G. Wells foresaw a genetic division of humanity into Eloi (or the master class) and Morlocks (or the servant class) in perpetual struggle against each other. At present we do not have to go so far. But let us weigh the advantages and disadvantages of future technological evolution.

On the one hand humans may thereby be liberated from many current drudgeries. Soon houses may be able to clean themselves, robots may produce meals on demand, cars may drive under remote instruction, and evolution of desirable characteristics could even be automated. All this seems unimaginable when so many still have to trudge miles to collect fuelwood and water.

On the other hand humans could well become dangerously vulnerable to technological breakdown, and thereby lose an essential measure of self-sufficiency. Already dependence on computers to run our complex systems, and reliance on electronic information transfer, are having alarming effects. Here industrial countries are far more vulnerable than others. Just look at the effects of single and temporary power cuts. More than ever individuals feel out of control of even the most elementary aspects of their lives.

For the longer term I hesitate to speculate. Are we a degenerate species because we have contrived that so many of us survive, thereby frustrating the processes of natural selection? Or can we safely proceed with secondary and even tertiary evolution?

Peter Ward once wrote:

"The future stretches before us not as one long dark tunnel but as a series of vignettes of variable clarity, like a long avenue punctuated by street lights of differing luminosity."

Cities will rise and fall. Tectonic plate movement will shift the relationship between land and sea. Changes in oxygen levels in the atmosphere may affect the viability of current forms of life. In any case plant and animal species will continue to change in shape and function. Humans may be no exception. Given the evolutionary significance of our brains and the current hazards of childbirth, we might imagine a sort of human marsupial in which women gave birth earlier in the reproductive process, and developed a kind of pouch.

Supposing our species fell victim to some natural disaster, as other species have so often done in the past, I wonder how long it would take for the Earth to recover from the human impact. How soon would our cities fall apart, the soils regenerate, the animals and plants we have favoured find a more normal place in the natural environment, the waters and seas become clearer, the chemistry of the air return to what it was before we polluted it? Driven by evolution, life itself, from the bottom of the seas to the top of the atmosphere, is so robust that the human experience could become no more than a short and certainly peculiar episode in the history of life of the Earth.

As the 17th century philosopher Thomas Hobbes said, as he approached death, "I am about to take my last voyage, a great leap in the dark". That is true of all living species, not least ourselves, now and for ever.