This book (Jablonka & Lamb Reference Jablonka and Lamb2005) is a well-written effort to deal with a topic that is a bit beyond the realm of familiarity for the average well-educated reader. That realm deals with the molecular underpinnings of evolutionary biology. Early on, evolutionary thinking is introduced in straightforward fashion, with Lamarck, Darwin, and August Weismann all given the recognition they deserve. The authors then present their case, noting how history has tended to leave out some of the aspects of the thinking of each scientist. Gregor Mendel, Hugo de Vries, William Bateson, T. H. Morgan, and the establishment of the field of genetics are all treated in this book, and Theodosius Dobzhansky and Ernst Mayr and the establishment of “the Modern Synthesis” are also dealt with, although here difficulties arise. To illustrate the interpretive twists in the issues presented, each chapter ends with a “dialogue” between a mythical inquisitor, I.M., and the authors, identified as M.E., which stands for the initials of their first names. I.M., in turn, stands for Ifcha Mistabra, which means “the opposite conjecture” in Aramaic, the language of the Biblical Christ.
Eva Jablonka is a professor at the Cohn Institute for the History and Philosophy of Science and Ideas at Tel Aviv University in Israel and is obviously familiar with Semitic languages. When the authors are discussing “Genes and Behavior, genes and language,” which is Chapter 8, the example depicted is in English, Hebrew, and Polish to illustrate some of the thinking of Noam Chomsky. The dialogues at the ends of each chapter are thoughtful efforts at articulating some of the various interpretations of the material being presented. The tenth and final chapter is a prolonged I.M. and M.E. dialogue summarizing the issues covered in the whole book. This is followed by 30 pages of chapter notes, which in turn are followed by 30 pages of bibliography, making the whole an admirably documented production. Throughout, line drawings by Anna Zeligowski illustrate the matters being presented. Ifcha Mistabra appears smoking a pipe in the cartoon on the cover, in the Prologue, and at the end of the last page of the text.
Any work that can offer an informed critique of the Universal Grammar outlook of the MIT linguist Noam Chomsky on the one hand, and then, on the other, note that methylated cytosines are very prone to change spontaneously into thymines – and that changing a C to a T in a DNA sequence could have serious consequences – is automatically going to earn the respect of the reader. Jablonka & Lamb (J&L) clearly are in command of a vast literature in linguistics and, if credible, of even more in biology and genetics. They present a view of “evolution in four dimensions”: genetic, epigenetic, behavioral, and symbolic/cultural, with the last being particularly important for the human part of the picture. Each of these dimensions gets a chapter, but perhaps the epigenetic chapter is the most crucial.
Epigenetic inheritance systems (EISs) are baffling to us because it is not clear how they work. The cells in each tissue, whether kidney, liver, heart, or whatever, divide to form more cells of the organ in which they are found, although their DNA is the same in each of the different kinds of cell. Presumably this is just the result of the cytoplasm in each cell simply replicating in the daughter cells, whereas the nucleus duplicates itself also but does not control the process.
Four types of epigenetic systems are discussed: self-sustaining or feedback loops; structural inheritance or templated assembly; chromatin-marking systems and their role in DNA methylation; and RNA interference (RNAi) which leads to the silencing of certain genes.
It is in the separation of genetics and epigenetics that there are going to be questions raised about the usefulness of the authors' efforts. Most evolutionary biologists emphasize learning about the genome and its control over the assembly of the organism, and the subsequent effects of selection, and are going to feel uneasy about the tack taken by J&L. The authors critically cite the approach taken by the esteemed John Maynard Smith and his coauthor Eőrs Szathmáry in their 1995 volume, The Major Transitions in Evolution, in which the picture of how evolution works is the one accepted by most evolutionary biologists. Genetic variation occurs and is then acted upon by selection to produce evolutionary change. As the authors under review declare, “there is no room in Maynard Smith and Szathmáry's evolutionary ideas for instructive processes, other than in human societies. This, we believe, is a mistake” (Jablonka & Lamb Reference Jablonka and Lamb2005, p. 344). Most of us in this business would disagree. It is true that much is not known about the details of genetic control, but, at the present time, their level of faith seems more like wishful thinking.
J&L also take issue with the views expressed by Ernst Mayr and John Maynard Smith in opposition to the inheritance of acquired characteristics, and they try to defend a kind of neo-Lamarckian stance. Again, this is something that most working in the field would reject.
Another point the authors do not face is the possibility that a single nucleotide or a codon triplet can often function as a single gene. They mention the recent estimate that the number of genes in the human genome may be as low as 25,000, although they suggest that it also may be “very much higher.” It has long been known that there are some 40 human hemoglobin variants inherited as single gene traits, and that each is the result of a single amino acid substitution (Baglioni Reference Baglioni, Crow and Neel1967). Amino acids, in turn, are specified by nucleotide codons, and often by one or two nucleotides. The human genome has 2.9 billion nucleotide base pairs (Wade Reference Wade2002), although, with the quantity of junk DNA in the genome, most of them are not coding for anything (Britten Reference Britten1986). Still, that is a huge number of base pairs, and the number of amino acids in a given human being is mind-bogglingly large. If each is produced by a single gene, then the number of genes present has got to be in the many millions at least.
