Following his last edition of the Origin of Species in 1872, Darwin spent much of the rest of his life searching for possible mechanisms, such as the pangenes in the blood, which would communicate information from the environment to the genome. In each of his six editions of the ‘Origin’, he stated that there were two forces within the mechanism of natural selection: selection itself and the conditions of life. Of the two, he claims that the latter is the more powerful. In so doing, he recognized that natural selection could only operate within the bounds of possibility, that is the environment. August Weismann claimed that conditions of existence had no place in evolution. His publication, the ‘All-sufficiency of natural selection’, was based on mutilation (cutting tails off mice and watching the next generation grow tails), which has nothing to do with Darwin’s concept of conditions of existence. Nonetheless, evolutionary biologists in general followed the line of the ‘all sufficiency’ theory and ignored Darwin’s conditions of existence, which in other words means the environment. Natural selection has a weak predictive power as it is based on random events. However, the conditions of existence have, by contrast, strong predictive powers that can be tested. The environmental views of two of the greatest evolutionists, Lamarck and Darwin, have been consistently ignored by most evolution theorists who came after them, continuing for over 200 years. Looking at the fossil record through the eyes of Darwin’s conditions of existence, not to mention the recent changes in height and shape over the last century, it is possible to draw important conclusions about the past and predictions of the future. With new knowledge of epigenetics, it is perhaps time that Darwin’s conditions of existence were given a second hearing.
David Marsh, Dip Ag, 37 Waterhouse Close, London W68DQ, UK
Nutrition and Health 21(1) 27-39
ª The Author(s) 2012
Reprints and permission:
Conditions of existence, environment, environmentally induced modification, natural selection, epigenetics, brain-specific nutrients
It is said that Charles Darwin died ‘almost a Lamarckian’. It is true that his first tutor at Edinburgh was Robert Edmund Grant, a Lamarckian anatomist. It is also true when it is said of Darwin that ‘he spent most of life trying to work out the exact mechanism’ whereby ‘conditions of existence’ (Darwin’s phrase, we now say environment, substrate or nutrition) cause variation in species. ‘But what is the actual cause of diversity?’ he asked in correspondence with a friend. In many ways this mirrors Lamarck, who also spent most of his life devoted to working out the same conundrum.
Today, although epigenetics has been around (under that name) for 50 years or more, it is gaining more attention since the completion of the human genome map a few years ago. Then it was revealed that we have far fewer genes than we expected, and that controller genes – switching on or off of different genes or blocks of genes depending on conditions – could be considerably more important than previously recognized. Epigenetic mechanisms were not revealed until the late 20th century.
The phenomenon of environmental variation had been an accepted fact of evolution since well before the turn of the last century, when it was known as ‘environmentally induced modification’. However, because such generational change often reverted to previous forms, it was not considered important. A clear example of this is seen in the fossil record in trilobites with nine sets of legs, then 11, then 13, then after thousands of years suddenly reverting to nine pairs of legs again. This points to a previous richness of the creature’s environment, which had enabled it to grow more sets of legs, suddenly feeling the pinch of shortage of building blocks, causing the creature to downsize. This is an example of what Darwin termed ‘plasticity’ of variation (Crawford and Marsh, 1989, 1995).
Darwin’s contradictions or the evolution of his thought become apparent only with the benefit of 150 years’ hindsight. During the last century and a half it was not so clear.
One can see the prescient vision of Darwin, his superb and intricate studies and analyses of both the minutiae and cascades of creatures – his cranial descriptive brilliance was perhaps to be mirrored later by August Weismann. They were both ahead of their time. And so it came to pass that both men succeeded in changing peoples' thoughts, creating a new paradigm which most of us have grown up accepting.
Now the scene is about to change once more. Fascinatingly, it is Darwin’s original thought processes on environmental effects that shine when considered with knowledge that is currently emerging in the epigenetic arena. For now we consider not only the initial effect of substrate or nutrition on chromosomal variation, but also what happens in further generations, when the initial epigenetic changes continue and we come across the crossword puzzle presented by genomic imprinting.
Thomas Kuhn: paradigm shift
The history of the theory of evolution is currently being brought alive with the realization that we are living within a period of paradigm change in evolutionary theory. Not every person in his or her lifetime experiences the excitement of such philosophical or scientific upheavals.
Recent discoveries concerning various environmental pressures affecting the genome and succeeding generations have brought this subject, known as epigenetics, alive. Philosopher of science Thomas Kuhn popularized the terms ‘paradigm’ and ‘paradigm shift’ in his book The Structure of Scientific Revolutions (1970). Its publication was a landmark event in the sociology of knowledge. Before Kuhn, the term had been used only within grammatical discourse. Since its first publication in 1962, it has become synonymous with patterns of scientific belief systems and the influences and conditions under which they change.
Galileo was imprisoned for his beliefs that the earth went round the sun, and, although later released from prison after disowning them, he spent the remainder of his days under house arrest – hardly a fitting prize for one who gained the reputation of being the ‘father of modern physics’.
Charles Darwin was vilified by the establishment for his beliefs – as was Alfred Russel Wallace – particularly by the Church, which is why he delayed publication for 20 years before being rumbled by Wallace. (This junior partner, who had arrived at the same conclusions as Darwin after a much shorter period of study and reflection, and then sent his paper to Darwin for his criticism, prompted Darwin to publish his findings.)
Jean-Baptiste Lamarck was not the first European to explain the unfolding of life in his book Philosophie Zoologique, but he was the first to popularize a theory of evolution. Lamarck’s first draft in 1797 was coincidental with publication by Charles Darwin’s grandfather, Erasmus Darwin, whose long and studiously boring poem Zoonomia echoed Lamarck’s beliefs. It is said they did not know each other; however, the Darwin family were conversant with the French language and so they could have been up to date with developments across the channel. Lamarck’s later versions appeared in 1803 and 1809 (Lamarck, 1873). This should come as no surprise, for the evolutionary soil had earlier been sown with the thoughts of Walter Johann Goethe and Jean-Jacques Rousseau (who gained a doubtful reputation during the French Revolution), who were influential during the 18th century.
Concentrating on Lamarck, it can be said that he was a man of huge importance. Although usurped by Wallace and Darwin (1859, 1872) 50 years later, he influenced half the world for 50 years. Lamarck’s beliefs were basically that God, when wanting a change (of species), altered the environment so that the creatures living in such changing conditions had to adapt, and adapt they did. It is tragic that he died impoverished and was buried in a pauper’s grave.
It is the author’s belief that he will recover his reputation as the ‘Father of Evolution’, a title which he enjoyed before being done down by M. le Baron George Cuvier and for decades later by European academics. Very much the aristocrat, Cuvier was not only a creationist, but was also a catastrophist – a school of thought which believed that every so often God wiped out all existing life and started over again.
It is curious that Cuvier, an establishment figure who held opposing ideas to Lamarck, was chosen to write the eulogy at Lamarck’s funeral. However, Cuvier himself died before delivering the eulogy, which was read by someone else. Cuvier’s (or the reader of the eulogy’s) ‘dirty tricks department’ provided a sly change in his eulogy, suggesting that Lamarck had said that ‘species changed by wishing or willing themselves to change (le desire)’, rather than them needing to change (le besoin). It would no doubt have caused poor Jean-Baptiste to turn in his grave.
Weismann’s theory of the continuity of the germ plasm
It was Professor August Weismann from the University of Freiburg, who played the next opposing move. In 1885 he published his theory of the ‘continuity of the germ-plasm’, an equal and opposite idea to Darwin’s concept of ‘pangenesis’, which was a seemingly wild hypothesis proposing that environmental changes became registered in the germ plasm – which in those days was improvable. Weismann, however, insisted on the absolute isolation of the germ plasm from ‘somatoplasm’ or other tissue of the body. (Germ plasm . . . the physical basis of inheritance . . . germ-cells are the reproductive cells, the opposite to somatic cell; primitive male or female element.) What he managed to persuade the scientific world of his day to believe was that, in modern terms, the gene-bearing DNA in reproductive or sexual cells lived a bunker-like existence, shielded from all environmental and somatoplasmic pressures with few exceptions (Weismann, 1894).
Isolation of the germ plasm theory
Weismann argued this absolute gulf with splendidly convincing rhetoric. Whilst the body gave of itself, and actually created the germ plasm, fed it, nurtured it and acted as its vehicle, it could never affect the germ plasm itself. Thus, in its splendid isolation, there could be nothing that could affect the structure of the genetic mechanism via the body tissue. This move is thought by some to have been a check to the direction that, in his later years, Darwin was moving towards, veering uncomfortably close to the ideas that Lamarck had had at the beginning of the century.
Indeed, Darwin, having been so utterly condemning of Lamarck, had taken his ideas on the effects of habit, or use and disuse (without giving any credit), and was seen to be playing into the hands of the opposing camp of the old-school naturalists and organic evolutionists, and possibly posing political, even theological, threats.
But Weismann’s insistence on the insulation of the genetic mechanism from any actions of the body put an end, for the time being, to this drift. His erudite argument, which was for his time scientifically remarkable, strongly reinforced the focus of attention on the ‘internal’, into the heart of the hereditary mechanism. Darwin had first taken the focus of attention into the organism, lessening respect for the chemistry and quality of nutrition (in those days little was known about nutrition).
Weismann strongly reinforced those ideas and was also responsible for the creation of neo-Darwinism. He went blind in later life, turning to theory from experimental work, and formulated his theory of germinal selection, according to which variation was ‘directed by competition for nourishment among ‘‘character-units’’ of the germ-plasm’ (genes had still not yet been discovered) (Weismann, 1894).
The theory was that by this mechanism it was possible for any change to move in the direction favoured by selection. This early suggestion of evolution’s involvement with food is quite stunning in view of contemporary research work, which makes it look very much as if the converse could be happening. Note: Danish botanist Wilhelm Johannsen coined the word ‘gene’ in 1909 (the word gene was derived from De Vries’ term ‘pangen’, itself a derivative of the word ‘pangenesis’, which Darwin (1868) had coined).
Through his ‘advanced’ thinking, Weismann removed even that aspect of the original Darwinism that brought the environment into consideration. He argued a powerful case for the ‘All-sufficiency of natural selection’ – the title of Weismann’s article replying to Herbert Spencer’s defence of Lamarckism.
Mendel and de Vries’ mutation theory
Mendel had originally published his paper in 1865, but it was born into a shadow cast by the worldwide excitement of Darwin’s success (Mendel, 1866). The paper was ignored and lay dormant for 35 years before its significance was discovered. The rediscovery of Mendel’s important paper in 1900 gave rise to other new schools of thought, which initially challenged the increasingly shunned Darwinism.
In fact it would have saved Darwin himself a lot of headaches had he realized Mendel’s discovery, for what was generally believed before this time was that the characteristics of the parents blended and after a few generations became lost in obscurity.
Mendel’s work showed that whilst certain characteristics might appear to be lost, they were still present but being carried as recessive genes. Then, when there was a fortuitous cross with another of the species, also carrying similar recessive genes, the character would show up again.
Darwin and others had put these phenomena down to atavism, or reversion to characteristics of the grandparent or great-grandparent. Mendel therefore explained the quantitative aspects of the hereditary mechanism. Mendel was indeed important, but his was a theory of hereditary mechanism, not a theory of evolution.
Mendel’s observations gave biologists the ammunition they needed to take this inward focus even further, and later molecular biologists would invert their gaze even more. Whilst most of the Darwin/Lamarck argument hung on the inability of research to isolate the suspected, or expected, ‘Lamarckian factor’, another part of the thinking could have been centred, subconsciously or otherwise, on the implications of Lamarck’s ‘holistic’ philosophy, which might have re-raised the spectre of religious domination that the evolutionists had been striving so hard and so successfully to avoid.
Furthermore, there would have been unpopular political implications which would have to be faced should the environment be discovered to be a formulating factor in evolutionary direction. These would have included more socialistic attitudes than were favoured in the eyes of those who supported the ‘survival of the fittest’ theory, which became an extension and refinement of the ‘right of might’ argument.
Evolution after Darwin – the eclipse of Darwinism
The power of public opinion has always been an invisible agent in the evolution debate. It could well have been a reflection of the moods of the time in the 19th century that the new theory of natural selection caught on in such a big way.
Natural selection’s attraction lay in two quite different areas. It was not only that what could easily be seen as an atheistic (although Darwin became agnostic) theory of evolution had arrived and gained scientific acceptability, but that there was then in existence a vast tidal wave of human emotion waiting to be ignited by just the spark of new, refreshing and revolutionary thought that Darwin and Wallace provided.
For so many centuries the Church controlled not only people’s emotional lives but politics as well. Morals, the work ethic, education and decisions concerning war or peace were all made in the name of the Church. In other words, life was stuck in the harness of that thinking and the mood was of longing for change. There was as much talk in the 1860s of the new ‘enlightenment’ as there was of the ‘new age of Aquarius’ in the 1960s.
Despite the enthusiasm of such moods in its early days, Darwinism was later to be severely challenged from within the scientific community itself. Roughly between the 1890s and the mid-1930s were decades filled with emotional and passionate debate, during which period there were some who thought that Darwinism would not survive. It is true that once again the blanket philosophy of (the new) Darwinism has become the subject of renewed criticism, being felt, as it is by many, to be lacking in crucial aspects which might be connected to certain major problems that our own species face today.
Sir Julian Huxley coined the phrase ‘the eclipse of Darwinism’ in 1942 in his book Evolution, The Modern Synthesis. Bowler, in his book The Eclipse of Darwinism (Bowler 1983), describes how Darwin’s theory was indeed covered by a great shadow for more than 30 years and how it emerged into brilliance again after some of the most ferocious debates in the history of science. It emerged refined, strengthened through suffering/criticism/challenges and the new discoveries of hereditary mechanistics, higher mathematics and population genetics, in a somewhat altered form – the neo- Darwinism of the ‘modern synthesis’.
Mention is made of public sentiment in evolutionary theory which could have been underestimated in the past. Indeed, some of the strongest contenders amongst the alternative schools of evolutionary theory fell foul of such public feelings during the battle for control during the ‘eclipse’, as we shall later see.
So, whilst we are considering largely a new scientific viewpoint, we shall also be considering the evolving needs (including emotional and philosophical needs) of ordinary people. What Darwin managed to do so successfully was to not only take us from the grips of the Church but also lead us from purpose to chance, and leave a corresponding void in our culture. Life had been reduced to a series of chance events with survival of the fittest being the nearest we get to a purpose/mover/driver/influence.
Fisher, Haldane and Wright: biometry and population genetics
The application of higher mathematics to genetics, from around 1917 to the mid-1920s, led to another startling discovery. Based on the work of the statistician Fisher and biologists Haldane in England and Wright in the USA, mathematical biology and genetics were successfully crossed, giving birth to a new hybrid.
The new science of mathematical population genetics established itself by showing that when applying the principle of natural selection to theoretical models, the effects of even small genetic changes at population level would result in the sort of overall change that Darwin himself was originally speaking of. Such changes could also be interpreted in Mendelian terms.
These discoveries were to unite Mendel’s ideas with Darwinism, which began to revive after its ‘eclipse’.
The modern synthesis
The excitement over these new discoveries was a reflection of the brilliant foresight of Darwin. That it took not only over 70 years but also the sophistication of higher mathematics for lesser mortals to come to similar conclusions was a significant step for the future emergence of the previously warring factions. But this stunningly accurate observation did not, even then, account for the actual cause or origin of diversity. This was pointed out by geneticists. What Darwin was seeing was a cause and effect phenomenon, the effect of which he called selection.
The causal mechanism of the change was simply explained as being produced fortuitously by nature, and therefore was ‘natural’. Perhaps the most common objection to his theory was that whilst selection could be seen to account for the progression of those best fitted to the environment (Darwin’s original term), it would not account for the production of those that were least fitted. For the other side of the coin of survival of the fittest was the elimination or extinction of those organisms whose design did not match the demands of the environment and the struggle for existence. On these grounds, selection could be doubted as the actual driving force.
But after Mendel’s ‘proof’ by population genetics and its ensuing success as a theory of evolution, the advances made in genetics and the understanding of hereditary mechanism were rapid, giving rise to the schools of molecular biology and genetic engineering that we know today. They joined forces with the neo-Darwinism of Weismann, recognizing the extraordinary power of natural selection but altering its role. Natural selection, they explained, worked at a population level on the ‘gene pool’ of the species, which is continuously being replenished by small changes. It is on these changes, Weismann convincingly argued, that selection then acts.
An explanation from CC Li, of the University of Chicago, in his book Population Genetics (1955), clarifies the situation described in this brief pre´cis: Gene mutations occur at random in nature at a certain low rate. The causes for mutation remain unknown (‘spontaneous’) . . . The most important single conclusion in the genetic studies of Mendelian populations is that there is no one all-important factor in evolution. The theory of isolation, of natural selection, of migration, of hybridisation, of mutation, etc., none of which is adequate by itself, are combined into one comprehensive theory which includes the additional factor of chance. Evolutionary changes depend on the interplay and balance of all factors.
This clearly reveals how all of the known factors must relate to the factor of chance and also highlights the omission of consideration of the chemistry of food and environment, not to mention the improbability that chance had anything to do with it, as Darwin himself had pointed out (Darwin, 1872).
The argument went on lengthily, often vehemently, until what became known as the ‘modern synthesis’ emerged triumphantly in the late 1930s and early 1940s, when the mutation theory of Hugo de Vries teamed up with the schools of biometry, population genetics and molecular biology in a new form of neo-Darwinism, the origins of which lay in the theories of Weismann. But for the first decade of the century these different schools had actively opposed each other. The story of the process whereby the modern synthesis emerged has, as mentioned above, been meticulously related by Peter Bowler, who comments: It is certainly conceivable that in the excitement generated by the synthesis of Mendelism and natural selection, some genuine problems may have been over-looked. The few scientists who argued that apparently discredited ideas contained a kernel of truth that would help to solve these problems were ignored until recently. Some modern biologists now believe that an even broader synthesis of the various modes of change is possible. The potential of their new approach remains to be determined of course, and there are still many sceptics who believe that the challenge to modern Darwinism is unnecessary. (Bowler, 1983)
Watson and Crick
In 1953, James D Watson and Francis Crick, along with Rosalind Franklin and Maurice Wilkins, discovered the structure of the DNA molecule, for which they won the 1962 Nobel Prize. In describing the double helix, they explained how information from the cell’s nucleus was translated via RNA to the cell (Watson and Crick, 1953). Their work reinforced the concept of the ‘primacy of DNA’ theory.Watson went on to head the Cold Spring Harbor Laboratory, raising major funds for basic science research. He was noted for administrative successes and appointed the head of the Human Genome Project.
These were some of the arguments going on over the last two centuries and more, before the discovery of epigenetics, that were termed epigenetic effects by CH Waddington in the early 1940s. The recent burgeoning of this subject to this day means that epigenetic mechanisms are more clearly understood.
Epigenetic change is the modification of the genetic mechanism (DNA) by environmental influences, causing reversible generational change in shape, form or function, most commonly by changing genetic ‘expression’ or ‘behaviour’.
In the history of evolutionary theory, ‘environmentally induced modification’ has been known and accepted since the turn of the last century. But – as we have already 34 Nutrition and Health 21(1) seen – because it caused a form of change that was reversible, it was not considered important. Today, the post-human genome map – which shows that we have only roughly one-third of the number of genes than previously thought – together with greater knowledge on the subject, means that it is quickly being realised that that viewpoint of scientists and naturalists of a century ago was misplaced.
Changing genetic expression means the same genome, the same shape or structure of DNA and behaving differently in response to changing conditions (or pressures) of the environment, sometimes referred to as ‘impact energies’.
Environmental pressures including chemical / substrate / nutritional / hormonal / emotional / atmospheric, etc., appear able to throw genetic switches on or off, and thus enable genes to make more of this protein and less of that depending on the supply of available nutrients or substrate chemicals.
For those of us not well versed in the subject of epigenetics and imprinted genes, Dr Joanna Downer’s background information is useful. She says, ‘There is far more to genetics than the sequence of building blocks in the DNA molecules that make up our genes and chromosomes’ (2002). The ‘more’ is known as epigenetics. What is epigenetics? ‘Epigenetics’, literally ‘on’ genes, refers to all modifications to genes other than changes in the DNA sequence itself. Epigenetic modifications include the addition of molecules, like methyl groups, to the DNA backbone. Adding these groups changes the appearance and structure of DNA, altering how a gene can interact with important interpreting (transcribing) molecules in the cell’s nucleus.
How do epigenetic modifications affect genes? Genes carry the blueprints to make proteins in the cell. The DNA sequence of a gene is transcribed into RNA, which is then translated into the sequence of a protein. Every cell in the body has the same genetic information; what makes cells, tissues and organs different is that different sets of genes are turned on or expressed.
Because they change how genes can interact with the cell’s transcribing machinery, epigenetic modifications, or ‘marks’, generally turn genes on or off, allowing or preventing the gene from being used to make a protein. On the other hand, mutations and bigger changes in the DNA sequence (like insertions or deletions) not only change the sequence of the DNA and RNA but also may affect the sequence of the protein as well. (Mutations in the sequence can prevent a gene from being recognized, amounting to its being turned off, but only if the mutations affect specific regions of the DNA.)
There are different kinds of epigenetic ‘marks’, chemical additions to the genetic sequence. The addition of methyl groups to the DNA backbone is used on some genes to distinguish the gene copy inherited from the father and that inherited from the mother. In this situation, known as ‘imprinting’, the marks both distinguish the gene copies and tell the cell which copy to use to make proteins.
What is ‘imprinting?
Imprinted genes don’t rely on traditional laws of Mendelian genetics, which describe the inheritance of traits as either dominant or recessive. In Mendelian genetics, both parental copies are equally likely to contribute to the outcome. The impact of an imprinted gene copy, however, depends only on which parent it was inherited from. For some imprinted genes, the cell only uses the copy from the mother to make proteins, and for others only that from the father.
Imprinting in genetics is not new but it is gaining visibility as it is linked to more diseases and conditions that affect humans. Centuries ago, mule breeders in Iraq noted that crossing a male horse and a female donkey created a different animal than breeding a female horse and a male donkey. In the modern scientific era, however, the initial evidence for parent-oforigin effects in genetics did not appear until the mid 1950s or so.
Then, in the mid 1980s, scientists studying mice discovered that inheritance of genetic material from both a male and a female parent was required for normal development. The experiments also revealed that the resulting abnormalities changed depending on whether the inherited genetic material was all male in origin or all female.
Around the same time, others discovered that the effects of some transgenes (genetic material transferred from another organism) in mice 21 differed when they were passed from the male or female parent. The first naturally occurring example of an imprinted gene was the discovery of imprinting in the IGF-2 gene in mice in 1991, and currently about 50 imprinted genes have been identified in mice and human. (Downer, 2002)
Gene expression is concerned with not only differentiation but also the way in which a cell behaves. Substrates can alter enzyme activity. The study of gene expression is now providing evidence that substrates can work by acting on DNA itself. Dr K Yokuyama in Japan has studied the synthesis of a membrane lipid using simple systems. He identified the specific region in a yeast DNA which coded for an enzyme, choline kinase, which was known to respond to levels of substrates for making membrane lipids. To obtain a clean experiment, he isolated this section of the yeast DNA and inserted it in to the genetic mechanism of a bacterial strain of Escherichia coli that did not possess these enzymes. This technique enabled him to examine the behaviour of the piece of yeast DNA free from the confusing effects of related systems in the yeast. He then proved not only that the bacterium produced choline kinase but also that the inserted gene made different amounts of enzyme depending on the amount and type of substrates fed to the bacterium. By deleting sections of the DNA code bit by bit, he was able to identify a section of the code which responded to the substrates in the medium and switch on the synthesis of the enzyme. These results are probably the closest to proof that external substrates are acting on the genetic mechanism.
Dr Yokuyama also discovered that the substrates that stimulated the gene expression for choline kinase also stimulated the expression of a related enzyme, ethanolamine 36 Nutrition and Health 21(1) kinase. Both enzymes are used for membrane growth. Such coincident expression offers a mechanism for the co-ordination of genetic expression (Yokuyama, 1988).
In Paris, Dr M Mangeney has shown that certain messenger RNA molecules which translate the DNA information for the cell to make proteins are under the control of insulin and glucagons, two hormones responsive to the nature of food. Both these types of information describe how external influences can manipulate the amounts of products the cell can make (in Crawford and Marsh, 1989, 1995).
Cairns et al
In 1988, John Cairns, Julie Overbaugh and Stephen Millar published ‘The origin of mutants’. They showed that the bacteria E. coli grown on a lactose medium responded in a manner which implied that a proportion of the bacteria have mechanisms for making only those mutations that adapted the cell to the presence of lactose, which they could use as an energy source. In other words, by plating the E. coli, which previously had no experience of lactose, onto a lactose medium bacterial, mutants arose that had the ability to use lactose in a manner which would not have been predicted had there been the odd random lactose utilizing bacteria present before the plating. They say, ‘The main purpose of our paper is to show how insecure is our belief in the spontaneity (randomness) of most mutations. It seems to be a doctrine that has never been properly put to the test’ (Cairns et al., 1988). As a mechanism they suggest a form of reverse transcription leading to ‘a directed mutation’, which basically means information flowing back from the cell to the DNA. ‘If a cell discovered how to make that connection, it might be able to make some choice over which mutations to accept and which to reject’. The original studies on such models led people to believe that natural selection was at work. However, in these latest studies it seems as though it is the substrate which is driving the reprogramming of the genetic information. This type of evidence on adaptive enzymes and directed mutation is only a short step away from an understanding of how such manipulations could ultimately be expressed in animal form.
It is perfectly plausible that the change in average human height since 1900 could have been induced by just such a mechanism. Change in form could be simply brought about by the response of the DNA and enzymes to changing inputs.
Epigenetic imprinting – Pembrey
Marcus Pembrey, Professor of Clinical Genetics at the Institute of Child Health in London, is a scientist who believes that one’s genes are shaped in part by one’s ancestors’ life experiences and that biology stands on the brink of a shift in the understanding of inheritance. The discovery of epigenetics, hidden influences upon the genes, he suggests, could affect every aspect of our lives.
At the heart of this new field is a simple but contentious idea – that genes have a ‘memory’, and that the lives of your grandparents, the air they breathed, the food they ate, even the things they saw can directly affect you decades later despite your never experiencing these things yourself; what you do in your lifetime could in turn affect your grandchildren.
The conventional view is that DNA carries all our heritable information and that nothing an individual does in his or her lifetime will biologically be passed to his or her children. To many scientists, epigenetics amounts to a heresy, calling into question the accepted view of the DNA sequence, the cornerstone on which modern biology sits. ‘Epigenetics’, Pembrey explains, ‘adds a whole new layer to genes beyond the DNA’. It proposes a control system of ‘switches’ that turn genes on or off and suggests that the things people experience, like nutrition and stress, can control these switches and cause heritable effects in humans (Pembrey, 2006a).
For those wishing to follow this exciting work further, the BBC broadcast an excellent programme on Pembrey (et al.’s) work entitled ‘The Ghost in your Genes’. As the programme explained: This work is at the forefront of a paradigm shift in scientific thinking. It will change the way the causes of disease are viewed, as well as the importance of lifestyles and family relationships. What people do no longer just affects themselves, but can determine the health of their children and grandchildren in decades to come. (Pembrey, 2006) ‘We are,’ as Marcus Pembrey says ‘all guardians of our genome (Pembrey, 2006).
Following his last edition of the Origin of Species in 1872, Darwin spent the rest of his life searching for possible mechanisms, such as the pangenes in the blood, which would communicate information from the environment to the genome. Weismann destroyed that idea with the ‘All-sufficiency of natural selection’, an idea based on mutilation of the sort the Jews, Muslims and Christians have been doing in their practice of circumcision of the male foreskin.
As they had been doing this for several thousands of years, he should have known that such mutilation was not what Darwin meant by the ‘conditions of existence’. What Weismann was trying to ‘prove’ was ‘the inheritance of acquired mutilations’ – despite the fact that the ‘docking’ of lambs’ and dogs’ tails had also been carried out for thousands of years, with lambs and puppies still being born with tails!
Nonetheless, evolutionary biologists and others have interpreted biology in the context of the ‘All-sufficiency of natural selection’. The problem here is that natural selection being based on random events has little predictive power. Prediction and testing is the hallmark of science. However, ‘conditions of existence’ has a predictive power that has been tested and proven many times over.
The human population is predicted to reach 9 billion by 2050. The wild catch of fish stocks, the last remaining wild food resource, reached a limit 20 years ago. Brain disorders are now overtaking all other burdens of ill health. These, along with global warming, demand recognition that a better understanding of Darwin’s ‘conditions of existence’ is of the utmost importance to addressing the challenges of the future. It is well past the time for a restoration of Darwin’s original thesis and to explain the ‘not ‘‘All-sufficient’’ theory of natural selection’ and Darwin’s passionate environmentalism.
This paper is based on the Cleave Award Lecture 2011, given before The McCarrison Society and guests on 22 November 2011. A second part of this lecture will be published later. In it I will look at some notable clinicians and researchers of this and the last century, who through their work supported both Lamarck’s and Darwin’s ideas regarding formulating power of the environment.
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Bowler PJ (1983) The Eclipse of Darwinism. Baltimore, MD: Johns Hopkins University Press.
Cairns J, Overbaugh J and Milla S (1988) The origin of mutants. Nature 3235: 142–145.
Crawford M and Marsh D (1989) The Driving Force. London: Heinemann.
Crawford M and Marsh D (1995) Nutrition and Evolution. New Canaan, CT: Keats.
Crawford MA, Leigh Broadhurst C, Galli C, et al. (2008) The role of docosahexaenoic and arachidonic acids as determinants of evolution and hominid brain development. In: Tsukamoto K, Kawamura T, Takeuchi T, Beard TD Jr and Kaiser MJ (eds) Fisheries for Global Welfare and Environment. 5th World Fisheries Congress 2008. Tokyo: Terrapub, pp. 57–76.
Darwin C (1859) On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life. London: John Murray.
Darwin C (1872) On the Origin of Species by Means of Natural or The Preservation of Favoured Races in the Struggle for Life (6th ed). London: John Murray, chapter 5.
Downer J (2002) Johns Hopkins Medical Institutes. Available at: http://www.hopkinsmedicine.org/press/2002/november/epigenetics.htm
Kuhn T (1970) The Structure of Scientific Revolutions (2nd ed). Chicago: University of Chicago Press.
Lamarck J-B (1873) Philosophie Zoologique. Charles Martin (ed) Paris: Savy.
Li CC (1955) Population Genetics. Chicago: University of Chicago Press.
Mendel G (1866) Experiments on plant hybridization. Proceedings of the Natural History Society of Bru¨nn.
Pembrey M (2006a) Epigenetics. Sex-specific, male-line transgenerational responses in humans.
European Journal of Human Genetics 14(2): 159–166.
Pembrey M (2006b) The ghost in your genes. Available at: http://www.bbc.co.uk/sn/tvradio/programmes/horizon/ghostgenes.shtml.
Watson JD and Crick FHC (1953) Molecular structure of nucleic acids: for deoxyribose nucleic acid. Nature 171: 737–738.
Weismann A (1893) The all sufficiency of natural selection. Contemporary review 64: 309 & 596.
Weismann A (1894) The Effects of External Influences on Development. Romanes Lecture. London: Frowde.
Yokuyama K (1988) 29th International Conference on the Biochemistry of Lipids, Tokyo, Japan, 19–22 September.