Lamarck's blacksmiths and the worm's genes
13 May 2005
This article by Dr Simon Harvey was the winning entry in the 2004 re:search writing competition.
In the late 18th and early 19th centuries it was observed that the sons of blacksmiths tended to have larger and stronger arms than the sons of weavers. Now, if you asked a biologist to explain this observation today, you’d probably get a series of questions such as who observed this? where did they grow up? what did the mother look like? what is the sample size? or even, can we swap the children at birth?
If you actually got an answer, it would probably focus on differences between the children in their patterns of diet and exercise, and on the effects of a higher quality diet and harder physical work on the growth and development of the sons. However, when presented with this observation about the blacksmiths, biologists of the 18th and 19th centuries came to a quite different conclusion.
It was, in fact, observations of situations like this that led the French scientist Jean-Baptiste Lamarck to develop a theory of the inheritance of acquired characteristics. This theory relied on two rules. The first rule stated that organisms responded to their environment by changing the way that they used a particular structure or organ, and that in response to this change in use they physically adapted to become better suited to their environment. The second rule said that these environmentally induced changes were inherited and, as such, would be passed on to the children. Accordingly, under this theory, blacksmiths exercised their arms as they worked and therefore developed big muscles, a trait that was then passed onto their sons.
Charles Darwin acknowledged Lamark as a great zoologist
Until the start of the 20th century this theory of evolution, which eventually came to be called Lamarckism, remained a popular alternative to Charles Darwin’s now widely accepted theory of natural selection. Given that at this time scientists had no idea about the mechanisms of genetic inheritance, apart from a then obscure Augustinian monk by the name of Gregor Mendel, Lamarckism was actually a pretty good theory and was just as plausible as Darwin’s. However, there is a small problem with it: today we know it to be completely wrong. If it were correct, that individuals passed on to their offspring changes they have undergone in their lifetime, then children would be born with pre-pierced ears and the children of body-builders would not bear thinking about.
So, what has all of this got to do with worms? More specifically, what does this have to do with my work on the small invertebrate nematode Caenorhabditis elegans that I spend my time working on?
Aside from the fact that Lamarck invented the word invertebrate, while Professor of the Natural History of Insects and Worms at the French National Museum of Natural History, there is a more interesting biological link between the worm and Lamarck’s theory. If we look again at Lamarck’s two rules, it is apparent that it is the second one that really gets his theory into trouble, since the kind of changes he was considering are just not heritable. However, this still leaves the first rule – that organisms respond to their environment by changing to become better suited to that environment.
The muscles of the blacksmiths and their sons are responding to their environment, and although this represents a quite trivial example of such an interaction between an organism and its environment, the phenomenon is widespread and there are many fascinating examples to be found in nature. For example, C. elegans has a quite striking interaction with its environment, such that under conditions unfavourable for growth and reproduction, instead of developing into an adult it can go into a form of stasis, developing into an arrested stage that is both environmentally resistant and long-lived. Once environmental conditions improve, the ‘arrested’ worm resumes development, growing into a perfectly normal adult.
The muscles of the blacksmiths and their sons are responding to their environment
Developmental switches like this are relatively common among nematodes and it is perhaps unfortunate for Lamarck that, limited as he was to studying preserved specimens, he could have had no idea about the varied and complex life-cycles of his worms.
It would be interesting to know what influence such knowledge would have had on the development of his theory of inherited characteristics. Biologically, such an interaction between an organism and its environment is termed ‘phenotypic plasticity’. This represents the ability of a particular individual to show one set of characteristics if it develops in one environment and a different set if it develops in another environment.
At present the genetic and molecular basis of any example of phenotypic plasticity is not known. However, it is hoped we can change that through analysis of the switch between normal and arrested development in C. elegans. This hope relies entirely on our understanding of the mechanism of inheritance, thanks to Gregor Mendel, and on the extensive existing knowledge of the biology and genetics of C. elegans. Identifying the particular genes that control this plasticity in our worm’s life-cycle is of great importance as, even with thousands of people studying it, a significant proportion of the genes that go into making our worm are complete mysteries. The completion of the human genome project has revealed a very similar situation – thousands and thousands of predicted genes about which we know nothing. Since relatives of many of these unknown human genes are also present in C. elegans, studying the worm will help us to work out what some of these unknown human genes do.
Additionally, it’s nice to think that some of the work currently being done on one of Lamarck’s invertebrates may lead to him being remembered with greater fondness. After all, Charles Darwin and other early evolutionists acknowledged him as a great zoologist and a forerunner in the study of evolutionary biology – as indeed he was.
Simon will spend his £500 prize on attending the 2005 International C. elegans meeting in America. This work was supported by the Natural Environment Research Council.
Simon Harvey/School of Biological Sciences