Inherently limited - a review of Evolution in Four Dimensions
Since the late 19th century, when scientists established beyond doubt that conception consists of the fusion between one sperm and one egg to form one cell, one of biology's chief tasks was to explain how all the information needed to make a complex organism could be contained in a single fertilised egg cell. When it was discovered that all cell nuclei contain chromosomes which are all replicated prior to cell division, biologists concentrated all their attention on those chromosomes as the containers of inheritable information. By the 1950s, it had been established that those chromosomes contain very long-chain molecules, known as DNA, whose linear sequences of bases contain coded instructions for making nearly all the molecules needed for the construction and maintenance of an organism's body. Furthermore, the method by which chromosomes become replicated was confirmed. Though the process is susceptible to accidental errors, it was adamantly maintained throughout the 20th century that chromosomes could not be changed as a consequence of experience
This belief had two important consequences. Firstly, it allowed neo-Darwinists to assert that all evolutionary changes were ultimately due to those accidental errors in chromosome replication. Secondly, it resulted in the discrediting of the pre-Darwinian theory of evolution known as Lamarckism. Lamarck, and his followers, maintained that organisms could change as a consequence of environmental effects or behaviour; this is not disputed, and has been observed to happen throughout the evolution debate. In order for those changes to be of any significance to evolution, they need to be passed on to subsequent offspring in some degree, and that is the adamantly-disputed claim that Lamarck and Lamarckists also made. The process whereby responsive changes get passed on to offspring is known as the inheritance of acquired characteristics or Lamarckian inheritance; it has been vehemently denied, and its adherents vilified and castigated, by neo-Darwinists throughout the 20th century.
Though there have always been Lamarckists, they have often needed to resort to vitalism, or other non-material influences, to justify their belief. Vitalists maintain that chromosomes are merely tool-kits which are at the disposal of the Life Force, which does learn from experience and changes the way it uses its tool-kits accordingly through the generations. As a development from vitalism, Rupert Sheldrake maintains that as-yet-undetectable morphic fields allow the ways in which organisms actually use chromosomes to be transmitted through space to the same chromosomes in other organisms. This transmission is most pertinent in the case of developing organisms. Thus, Sheldrake too has been vilified by the neo-Darwinian scientific establishment.
Since the 1970s, many biologists have moved on from the linear sequence in genes, which are the sections of chromosomal DNA that get expressed to form useful molecules, to the issue of gene expression. Though this is an enormously complicated issue, involving the products of other genes as promoters, enhancers and inhibitors, neo-Darwinists remain convinced that it is all ultimately genetically determined, though there are often environmental triggers. In other words, they do not believe that organisms can inherit a tendency to express or not express any particular gene other than as a consequence of their own genetic make-up. If there could be shown to be an inheritable component to gene expression, based on previous experience, that would constitute evidence for Lamarckism.
Now we have an Israeli philosopher, Eva Jablonka, and a British biologist, Marion Lamb, whose book, "Evolution in Four Dimensions", attempts to justify their belief in Lamarckian inheritance in scientific terms. They fervently maintain that there is much more to inheritance than genes, and that their three other modes of inheritance - epigenetic, behavioural and symbolic - are Lamarckian. With regard to the behavioural and symbolic modes, this book does not contain anything particularly contentious, except their belief that changes are inheritable, though they provide no mechanisms for how that might occur (The examples they give of a pregnant mother's eating habits affecting the food preferences of her offspring does not constitute inheritance at all). They claim that the learned behaviour patterns of animals, originating as copying of adults by the young, and the use of symbols by humans mainly in the form of language, have been cumulative, to the point of sometimes becoming instincts, through inheritance. The reason I say it is not contentious is that neo-Darwinists also claim that such characteristics can increase over generations, but they separate out the inheritable genetic component and the uninheritable learned component. Ultimately, it is the choice of every individual to decide, based often on pre-conceptions, whether the learning itself is cumulative.
Much more contentious is the issue of epigenetic inheritance. Epigenetics was coined by the late maverick geneticist, Conrad Waddington, who was a champion of the apparent inheritance of acquired characteristics, which he tried to explain in neo-Darwinian terms. He defined epigenetics as the branch of biology which studies the causal interactions between genes and their products which bring the phenotype into being. For the purposes of this book it concerns those chemical processes and changes that go on in a cell that are not instigated by the cells own genes. Since the 1950s, there has been an escalating increase in the knowledge we have of all the complex chemical processes that go on in every living cell. Amongst other things, it has recently been established that chromosomes are not as invulnerable to change as they were previously thought to be. Chromosomes are not just composed of linear sequences of DNA. The DNA strands are wrapped around protein molecules, which can stretch out or bunch up to make genes more or less accessible in different cells, and there are various ways in which genes can acquire marks which promote or inhibit the expression of those genes. These marks, which are usually molecules that attach themselves to the DNA strands in particular places within the chromosomes, can originate within body cells in response to experience. Thus, acquired characteristics have been described in molecular terms.
Furthermore, when marked chromosomes are replicated, the replicas can contain the same marks as the original. This is believed to occur through a template effect, whereby the cell uses the original as a template for the replica. The template effect is also pertinent to another issue in biology - that of protein folding, which Jablonka and Lamb give some attention to. The function of protein molecules does not depend on their linear sequences, nor upon their chemical attributes, but upon the specific shapes that they fold up into. A common view is that the particular shapes that newly-produced protein molecules adopt are determined by the cell's use of existing identical folded protein molecules as templates. This view has been accentuated by the existence of prions (which cause diseases such as scrapie, BSE and CJD), which are mis-shapen proteins that have the same linear sequences as the proteins they 'should' have been. Prions increase in frequency within any organism that they infect, and that is due to their having a template effect upon the 'proper' proteins.
Jablonka and Lamb provide lots of evidence, acquired by behind-the-scenes scientists in recent years, that during cell division, and other forms of asexual reproduction, the acquired chemical attributes of a cell are transmitted to its progeny. In other words, during asexual reproduction, Lamarckian inheritance does occur. They even supply a mechanism whereby some types of specific chromosome marker, known as small interfering RNA molecules, can be replicated in one cell, and the replicas can be moved to other cells, where they affect the relevant chromosomes in the same way. However, these siRNAs are of limited applicability to understanding Lamarckian inheritance, and there is no evidence yet that they can migrate from body cells all the way to the sex cells.
And that is where this book fails: it offers no mechanisms whereby the induced changes to chromosomes within body cells get transmitted to the single fertilised egg. And that is what is needed in order to explain Lamarckian inheritance. If they had suggested that their template effect might be long-range rather than just in situ, that might have been enough, but they probably felt that such a suggestion would be moving into Rupert Sheldrake territory, and hence be scientifically unacceptable. If they had come clean in admitting that, though they believe in Lamarckian inheritance in sexually-reproducing species (which they undoubtedly do), they cannot account for how it occurs, that would have been satisfactory. But they seem to be pulling the wool over the reader's eyes by avoiding the issue of how changes to chromosomes in body cells get transmitted to fertilised eggs.
Instead, with regard to sexually-reproducing organisms, they resort to neo-Darwinian mechanisms, such as the natural and sexual selection of those organisms which do responsively adapt to change, leading to a genetically-determined, increased tendency to do so, as their explanation for apparent Lamarckian inheritance, just as Waddington had done. However, even if Lamarckian inheritance is only apparent, rather than real, that should be enough to vindicate all those believers in it, and to establish Lamarck's rightful place as an evolutionary pioneer, rather than as a vilified scapegoat.
Where Jablonka and Lamb's book does succeed is in giving a respectability to Lamarckism which it richly deserves.
That brings me on to the question of who the intended reader of this book is. The book is far too technical and inaccessible to appeal to the lay reader of popular science books. The dialogues at the end of each chapter, between their composite self and a created sceptic, are merely irritating (not least because their creation cannot see their glaring omission), and would surely have been better if they had hired a real sceptic. Despite the cartoon illustrations, it is not an entertaining read in the way that, for instance, the books of Richard Dawkins or the late Stephen Jay Gould are. That leaves us with scientists, or serious-minded people with some scientific training, who will not only tend to be resistant to the essential message, but will also probably see through the gaping holes, and they will be given no reason to doubt their faith in neo-Darwinism. In conclusion, this book is a worthy attempt to present a lot of new evidence that there is more to inheritance than genes, but it is unlikely to change anyone's opinions and it is not going to set the world on fire.
Hugh Dower MSc October 2005
As a postscript, see also the essay, "Lamarckian Inheritance From Epigenetics"