Karl WhitburnShaping Life:Genes, Embryos and Evolution
by John Maynard Smith
Weindenfeld and Nicolson, London, 1998
ISBN: 0 297 84138 6
book review for New Scientist
Evolutionary theory is based upon why the bodies are the way they are and embryologists are concerned with how the genes build them that way. These two approaches are predominantly seperate in their theories but Maynard Smith, in this book, tries to argue that the theories underpinning these groups are more ideological than scientific. He claims that advances in science underpinning both viewpoints are pulling these two seperate theories together.
John Smith's opinions are based around the fact that developmental changes that occur are dependent on embryological changes and evolutionary changes. He states that an understanding of evolutionary changes would be transformed once we have an understanding of embrology and that developmental genetics would enhance that understanding. An understanding of development is paramount if we are to understand the changes in morphology due to gentic modification.
There are many examples in the book to support the need to understand changes in genetic structure in respect to changes in development. Genes that are modified have the same effects across species as highlighted in the book.
One example is the mutation of a gene in the mouse that once mutation has occured causes that a mouse is born without eyes. This gene in its normal form transfered to the fruitfly causes that an eye is formed where-ever this gene is placed, not a mouse eye but a normal eye. Changing developmental genes causes a change in development of the insect. As this gene has existed for millions of years throughout evolution it is possible to deduce that this gene is existent in both mouse and fly. Evolutionary transformations are evident in embryolic construction and that the gene must have had some previous function before it controlled the location of the eye. The sequence of activation of these genes is important for an understanding of embryos and evolution.
Modification of certain genes has been done in the embryonic state as well, to determine the formation of certain body parts. This is important to evolutionary biologists as the alteration of certain genes causes that certain body parts are still formed despite drastic changes in their genetic structure. As can be seen in the example above, simply transfering genes from one species to another does not imply that the developoment of that part will form outside the genetic constraints of that species.
John Smith also argues that structures are formed by a consistent genetic blue print and that theologists who believe in self-organised principles are neglecting this theory at their peril. This has been proved in earlier discussion, that alteration of genes does not necessarily mean that the structure will alter, there is a set series of events that happen during development that cannot be altered.
Genes do not in themselves form these complex body parts but rather that the amino acids in a protein are formed and forced to act by the intervention of genes. At the embryonic state genes are fired at certain stages and proteins are acted upon in order to carry out their required formation of body parts. A greater degree of understanding of genetic structures needs to be found in order to apply large changes to embryonic formation as well as evolutionary changes.
At this point it is important to state that small changes have an effect on embryonic development and that large changes have an impact on evolutionary development. Modularity (accuracy and repeatability) are important consequences to consider in respect of evolution. Small changes allow that gradual evolution occurs and that body formation plans are preserved. Therefore small changes are important for embryonic development as well as evolutionary changes as they can easily be understood if accurate and repeatable. Large changes effect the whole genetic firing structure and make interpretation and understanding difficult.
It would appear then that organisms are not self organised but rather follow a certain genetic blue print. Self organised organisms would not yield modularity whereas the ability to understand what should happen and then testing what did happen is easily understood following this blue print principle.
The basic fact offerd by this book is that developmental genetics have served to offer a basis for the two theories of evolution and embryolysis to come together and combine the two theories. Although they often strive to remain in two different camps, gentics has fueled John Smith's opinions that why the body is the way it is and how the body is built that way are intertwining disciplines. Small changes in the embryonic state have a direct impact on the evolutionary processes of species, embryolysis is altered with small changes in the genetic firing of certain genes and these changes are evident in respect to evolution. It would appear from his discussion that it is almost impossible to now keep the two theories seperate from each other. Modularity enables biologists to study both theories, small changes are repeatable and give rise to accurate analysis of bodily alterations and these alterations over time.
This book is a must read for both camps, not least for the fact that they may enable each to understand the others theories. One cannot live or function without the other. An embryolysist cannot study alterations of genetic structure without studying these alterations over time and an evolutionist cannot study evolution without the research available by immediate small changes is genetic structure that effect the species at the embryonic stage.
The book does argue constructivly that both theories should no longer be kept apart and, true, that both theories can be enhanced by developmental genetics but this argument could have best been served with a greater understanding of the theories used by each. One is left believing that the argument is made and decisive but to what depth do both theories go to in their beliefs?
Karl Whitburn is studying Knowledge Based Systems at the University of Sussex in Brighton, England.