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Reviews

Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life

by Eva Jablonka and revealing the entire software that sions of that they consider comes with the human hardware. important. In each of these dimen- Marion J. Lamb Darwin’s open-mindedness about sions, they present up-to-date ideas the possible forces of evolution is the but at the same time remind the read- Reviewed by Bernhard Haubold, starting point for Evolution in Four er of classical observations that would Fachhochschule Weihenstephan, Dimensions: Genetic, Epigenetic, have undermined the ‘DNA as soft- Germany Behavioral, and Symbolic Variation in the ware’ metaphor had their significance History of Life by the evolutionary been fully acknowledged. In The Origin of Species, published biologists Eva Jablonka and Marion J. The first dimension they discuss is in 1859, Charles Darwin described Lamb. Their book is aimed at anyone the genetic. A central tenet of contem- evolution as a process subject to interested in evidence that under- porary evolutionary thinking is that diverse influences. Natural selection, mines a strictly gene-based mutations, the raw material of evolu- of course, leads to adaptation in a perspective , as the authors hope to tion, are random. In other words, it manner similar to the changes elicited convince their readership that “DNA is believed that there is no code for by breeders of pets or livestock. is not the be all and end all of heredi- changing the code. Jablonka and However, organisms might also dis- ty”. Ever since that winter day in 1953 Lamb introduce the reader to the play neutral characteristics, which when Francis Crick told astonished debate about non-random, adaptive have no effect on their fitness. In lunch guests at the Eagle pub in mutations among microbiologists addition, and rather surprisingly for Cambridge that he and Jim Watson during the late 1980s and 1990s. More the modern biologist, Darwin went had just solved the secret of life by persuasive, however, is their insis- along with the conventional wisdom unravelling the double helical struc- tence on the significance of the well- of his day and believed acquired char- ture of DNA, this molecule has, to all known fact that cells can alter their acteristics to be heritable. Since then, intents and purposes, been the ‘be all own DNA through various mecha- and computers have been the and end all of heredity’. For biologists nisms, including somatic mutation decisive additions to evolutionary brought up in the growing excitement and selective amplification. thought. Their combination has led to of that culminated The second dimension is the epi- a distinctive reinterpretation and in the Human Genome Project, the genetic, which encompasses all those refinement of Darwin’s great idea. In supremacy of DNA is part of a shared characteristics of cells and organisms 1976, the UK evolutionary biologist culture that has become so entrenched that are heritable without being writ- Richard Dawkins succinctly stated the that it is hard even to recognise. But ten into a genome’s DNA sequence. resulting new paradigm in the preface Jablonka and Lamb make a convinc- Although liver and brain cells contain to his influential book, The Selfish ing and level-headed case for a more the same DNA, they have very differ- Gene: “we are survival machines – pluralistic view of evolution and ent heritable morphologies and func- robot vehicles blindly programmed to heredity. The authors avoid the ant- tions. Behaviour constitutes the third preserve the selfish molecules known agonistic tone of The Selfish Gene dimension. The behaviour of the as genes.” From this point of view, the school of debating and patiently young is guided in non-genetic ways sequence of the human genome pub- explain the nuts and bolts, as well as by that of their parents. Finally, sym- lished in 2001 holds the promise of the implications, of the four dimen- bolic inheritance systems, foremost

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among them language, make up the fourth dimension. Having described their four-dimen- The Ancestor’s Tale: sional model of evolution, Jablonka and Lamb continue by showing how these dimensions interact. As before, A Pilgrimage it is classical work that is most illumi- nating. For example, the authors cite Waddington’s experiments from the to the Dawn of Life 1940s with heat-shocked Drosophila which demonstrated the phenomenon of ‘genetic assimilation’. Here, select- ing for an inducible phenotype leads by Richard Dawkins Today, the inversion of the arrow to it becoming constitutive and stably of time has a strong tradition among heritable after only a few generations. Reviewed by Bernhard Haubold, evolutionary biologists. If we start Today, genetic assimilation as well Fachhochschule Weihenstephan, with, say, three copies of the human as many other genetic phenomena are Germany alpha-haemoglobin gene and look understood in molecular detail and back in time, we will reach a point at the reader is given some of this infor- There is a natural way to tell a tale: which two of the three genes were mation where appropriate. The mod- begin at the beginning and end at the derived from a common ancestral erately technical nature of these pas- end. Standard biographies, for exam- gene. At that point, two alpha-haemo- sages is mitigated by careful avoid- ple, start with the forebears, in many globin lineages fuse. Such a fusion is ance of unnecessary jargon. In addi- cases the grandparents, and end with also known as a coalescence event, tion, each chapter concludes with a the protagonist’s death. So the end is and hence the corresponding theory delightful dialogue in which the clear, but the beginning is potentially is called coalescent theory. Moving themes introduced in the main section fraught with the difficulty of deciding further back in time, we reach a point are playfully varied. This makes the which ancestors to describe. After all, where the last two remaining lineages book not only thought-provoking, but one person has two parents, four fuse in another coalescence event. also fun to read. We may be blind grandparents, and 2n+2 n-great-grand- This is known as the most recent com- robots, but some of these robots are parents. An elegant technique to mon ancestor of the genes. It is of perceptive enough to see the limited avoid the thicket of ancestors is con- fundamental importance for evolu- fruitfulness of this point of view. I tained in the Bible, in which Luke, the tion, since any mutation that hap- thoroughly recommend Jablonka and biographer of Jesus, tells the genealo- pened further in the past affected all Lamb’s book to anyone interested in gy of his subject by starting with genes equally and hence is invisible an exciting alternative. Jesus and ending with Adam. As a in the present copy of the genes. man of his time, Luke only mentions Consequently, there is no use in Details the fathers, thereby converting an pursuing the history of a sample of Publisher: MIT Press exponentially growing, unmanage- genes beyond their most recent com- Publication year: 2005 ably large bi-parental genealogy into mon ancestor. Similarly, there is no a lean uni-parental genealogy. sense in telling the history of life ISBN: 0262101076 In contrast to human individuals, beyond the last common ancestor of two animal or plant species are all creatures alive today. So, as with usually derived from a single ances- biographies, the end of the story is tral species. Biological species there- clear, while the beginning is less clear, fore naturally form uni-parental because evolution has as many ends genealogies. In his latest book, The as there are extant species. But of Ancestor’s Tale: A Pilgrimage to the course, we are mainly interested in Dawn of Life, Oxford biologist Richard ourselves and this is where Dawkins Dawkins takes advantage of this fact starts his magnificent account. by giving a popular but richly Moving backward in time, we are detailed account of evolution starting joined along our lineage by 39 other at the end and time-travelling back- branches of the tree of life. These wards to the beginning of life. include, among others, apes, mon-

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