SOME things should not be mentioned in polite society, even among evolutionary biologists, who admittedly have bizarre ideas about what constitutes 鈥減olite鈥�. For example, it is close to blasphemy to speculate about the level at which natural selection acts, or about the unit of heredity. For it is written 鈥渢he fundamental unit of selection 鈥� is the gene, the unit of heredity鈥� (The Selfish Gene).
鈥淪peculating about鈥he unit of heredity is close to blasphemy鈥�
The 鈥渟elfish gene鈥� metaphor created by Richard Dawkins in his 1976 book has so dominated that discussion about other levels of selection or forms of inheritance has hardly been taken seriously. Yet in a packed room at London鈥檚 Institute of Contemporary Arts recently, professors did just that 鈥� albeit without Dawkins. Their message: too much emphasis has been put on the gene-centred approach, there is more to evolution than orthodox genetics.
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Eva Jablonka, the principal speaker and an evolutionary biologist at Tel-Aviv University, Israel, believes there are four 鈥渄imensions鈥� to evolution: genetic, epigenetic, behavioural and symbolic. For the ICA, she and the others concentrated on the second aspect 鈥� the one furthest from the selfish gene model.
Jablonka is one of a growing band of scientists who argue that non-genetic information affecting development is routinely passed from one generation to the next. As if that wasn鈥檛 enough, she calls the process Lamarckism. This is almost frothing-at-the-mouth heresy. The theory, dead for years, is attributed to 19th-century French biologist Jean-Baptiste Lamarck, who believed that characteristics acquired during a lifetime are heritable.
Jablonka, however, has spent 20 years arguing a rather different Lamarckism. 鈥淭hings hitchhiking on genes lead to different interpretations of that gene,鈥� she told the meeting. This heritable, non-genetic 鈥渉itchhiking鈥� is known as epigenetic inheritance.
There are many examples of heritable changes transmitted by something other than genes. Last year, a US study showed that an initial exposure to two pesticides reduced sperm counts in at least the subsequent four generations of male rats.
The effect did not seem to be the result of changes in the DNA sequence, making it the first time any chemical had been shown to cause any heritable effect other than by random mutation (快猫短视频, 11 June 2005, p 7). And earlier this year researchers in London and Sweden revealed that nutrition and smoking in early life can be passed down the male line to influence the health of sons and grandsons (快猫短视频, 7 January, p 10).
Some scientists seem to be unwilling to accept this notion. Dawkins, for his part, dislikes the term 鈥渆pigenetic鈥� because it refers to a historical, rather arcane, school of embryology. It seems odd to object for this reason; perhaps Dawkins fears for the selfish gene鈥檚 legacy.
However, if 鈥渆pigenetic鈥� is contested, how much worse is 鈥淟amarckism鈥�? Much better, said Patrick Bateson of the University of Cambridge, the other main speaker, to jettison it and stick with 鈥渆pigenetic inheritance鈥�.
Other evolutionary biologists such as Mary-Jane West-Eberhard of the Smithsonian Tropical Research Institute in Costa Rica and Massimo Pigliucci of Stony Brook University, New York, also think Jablonka would do well to drop the outdated, inflammatory term. They agree, though, that the gene-centred approach does not have enough explanatory power to account for the variety and complexity of organisms.
Reductionism has gone as far as it can, said Bateson, and adaptation as Darwin described it may not be enough to explain all aspects of speciation. This doesn鈥檛 detract from classical Darwinian explanations 鈥� it adds to them. Nor does it detract from the revolutionary insights of the 鈥渟elfish gene鈥� approach. It鈥檚 more that the approach shouldn鈥檛 hinder new understanding.
Not that long ago, a distinguished Oxford biologist announced that behavioural ecology (the evolutionary explanation of animal behaviour) was dead. The big questions had, he said, been answered. If he was arguing that we know how adaptations arise and are passed on, then the ICA speakers showed how wrong he was.
The final irony is that evolutionary biology hasn鈥檛 been this exciting since Dawkins published The Selfish Gene 30 years ago this year.
