Dear Mr Darwin: Letters on the Evolution of Life and Human Nature

  • Gabriel Dover
Weidenfeld & Nicolson: 2000. 268 pp.£20
Credit: DAVID NEWTON

In 1876 Charles Darwin contributed £10 — a substantial amount at that time — to the costs of the criminal prosecution of Henry Slade, a renowned spiritualist medium. Slade, his accusers charged, was a fraud, and his séances were merely elaborate exercises in legerdemain. Remarkably, the case pitted the two discoverers of natural selection against each other: Alfred Russel Wallace, author of an approving book on spiritualism, was the defence's star witness. Despite Wallace's characterization of the defendant as an “earnest inquirer after truth in the department of Natural Science”, Slade was convicted. Darwin was delighted; he had no time for the “clever rogues” who preyed upon grieving relatives anxious to contact a loved one.

Darwin, who died in 1882, may now have cause to reconsider his attitude towards posthumous communication as he himself has recently taken to holding forth from beneath the flagstones of Westminster Abbey. The medium in this case is geneticist Gabriel Dover, whose book, Dear Mr Darwin, comprises a series of letters between Dover and Darwin. Dover brings Darwin up to date on evolutionary biology since 1882, and Darwin, for his part, supplies appreciative yet inquisitive responses.

Things start rather formally — it's “My Dear Dover … Ever your most truly, Charles Darwin” to begin with — but become increasingly chummy as the correspondence develops — it's “Dear Gabby…. Your most sincere friend, Chas. Darwin” by the end. The gimmick is almost painfully cute, but Dover handles it deftly: he is not unduly deferential, and his Darwin not overly impressed by what Dover has to say. The result is a quirky but readable account of the Dover perspective on modern evolutionary biology.

Darwin's education, however, is in idiosyncratic hands. At the outset, Darwin must predictably swallow doses of Mendel and Hardy-Weinberg, but the textbooks are then quickly forsaken when, on the second page of Dover's second letter, we run into his pet theory, ‘molecular drive’. This, Darwin learns, is, along with natural selection and genetic drift, one of “the three forces of evolution”. Much of the book is dedicated to explicating molecular drive and to justifying its exalted place in Dover's pantheon of evolutionary forces.

Dover introduced the term in the early 1980s after DNA-sequencing studies of multi-gene families — groups of related genes that often sit side by side along chromosomes — had revealed a striking and unexpected evolutionary pattern now known as ‘concerted evolution’. Within a species, all members of a gene family may be identical, or at least very similar, whereas between even closely related species we see plenty of sequence divergence between homologous gene families. The homogenization of gene-family members within species is caused by a number of simple and well-understood genetic processes, primarily unequal crossing over and gene conversion. Molecular drive is, in Dover's words, an “umbrella term” covering these and other “non-Mendelian mechanisms of inheritance”.

Does molecular drive really rank beside selection and drift as one of the primary determinants of evolutionary change? Hardly. Darwin distinguished between two fundamental aspects of the evolutionary process: the genesis of variation, and the subsequent fate of that variation. In creating new configurations of existing genetic variation, molecular drive definitely contributes to step one. But does it contribute to step two? In principle, a variant can indeed spread through a gene family by molecular drive, especially when there are asymmetries in the drive process. For example, gene conversion is sometimes ‘biased’ such that an a allele is more likely to be converted to an A than an A to an a; such a situation may result in a molecularly driven increase of the A allele.

But crucially, the ultimate fate of any variant, whether subject to molecular drive or not, is determined by its impact on fitness: natural selection will intervene if it either enhances or diminishes its bearer's chance of reproduction. If the variant has no such impact — it is selectively neutral — then genetic drift is usually the major player, although molecular drive may sometimes also play a role. Molecular drive's contribution to the second phase of the evolutionary process is thus subordinate to the 'traditional' forces determining the fate of genetic variation in natural populations. Molecular drive is an interesting evolutionary phenomenon, but it is false advertising to bill it as a third major force of evolution.

Dover's Darwin, whose critical facilities may have been dulled by a century or so underground, is more readily convinced of molecular drive's significance than I am. Having scripted Darwin's endorsement of his theory, Dover then settles down to enjoy his new role as Darwin's speech-writer. Responding to a lengthy Dover diatribe against Richard Dawkins, whose “selfish genery is genetically misconceived, operationally incoherent and seductively dangerous”, Darwin reports that he will conscientiously hunt up Dawkins's books in a library: “I hope they are not filed under ‘Science’!”.

Dear Mr Darwin, however, is not confined to molecular drive and having Darwin say nasty things about Richard Dawkins. Dover writes at length on recent advances in developmental genetics, and adds his voice to those objecting to evolutionary psychology's insistence on attributing every quirk of human behaviour to the action of natural selection. Given that evolutionary psychology is an implicitly genetic theory (a trait must have a genetic basis to be subject to natural selection), it is interesting to note that many of its most persistent critics are geneticists.

Dear Mr Darwin is an engaging tour of Dover's passions, even if some are announced with more fanfare than they merit. Let us hope, however, that Dover's communications with Darwin do not create a literary fad based on the harassment of dead scientists. The thought of Linnaeus being badgered by manic modern cladists is alarming. On receiving one of Wallace's spiritualist publications, T. H. Huxley replied, “I never cared for gossip in my life, and disembodied gossip, such as these worthy ghosts supply their friends with, is not more interesting to me than any other.”