GMW: What Darwin really thought

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GMW: What Darwin really thought

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Sat, 23 Jul 2005 11:50:13 +0100

 

 

 

 

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Genetic engineering and the dogma on which it is based of a single gene

determing a single trait is increasingly shown to be at odds with a far

more complex, interactive and open biological reality.

 

EXCERPT: " think about the fact that humans are just under 99%

genetically identical to chimpanzees, yet no one would confuse the

two. The

origin of the differences between the two phenotypes lies in their

development, which in turn depends on which genes are switched on or

off at any

time - a process regulated by the cellular environment in which the

genes are embedded. Genes do not exist in isolation, but as part of a web

of interactions extending in time as well as space.

 

" Indeed, as more and more is learned about the complexities of these

processes, the concept of " the gene " as a reified DNA sequence tends to

dissolve... " - Steven Rose (What Darwin really thought - below)

 

Elsewhere Steven Rose has written, " There have been huge advances in

genetics knowledge over the past three decades. But in that same time

the

claims made by the geneticists have far outrun their actual

achievements. There's also now a big industry built on all this. The

whole biotech

industry is based on hope and promise, and those are very powerful

driving forces. Everybody's hoping their investment - be it financial,

political, scientific or even philosophical - in genetics will pay off.

 

" It's rather like what happened at the end of the [second World] War

when physicists persuaded governments that a vast investment in

nuclear power would pay off in infinitely cheap energy. What happened?

We got Chernobyl. "

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What Darwin really thought

 

Four Dimensions by Eva Jablonka and Marion Lamb is a lucid book that

restores subtlety to evolutionary theory, says Steven Rose

 

The Guardian, Saturday July 23, 2005

http://books.guardian.co.uk/reviews/scienceandnature/0,6121,1534168,00.html

 

Evolution in Four Dimensions

by Eva Jablonka and Marion Lamb

472pp, Bradford Books/ MIT, £22.95

 

Charles Darwin's great insight is based on a simple syllogism: (a) Like

begets like, with variations; (b) all creatures produce more offspring

than can survive to reproduce in turn; © those most fit - adapted -

to the environment are more likely to survive; and therefore (d)

favourable variations will be preserved and species will evolve -

change over

time. This is natural selection, and its logic is irrefutable - the

philosopher Dan Dennett called it a universal acid. This is why

" Darwinism " is not merely a " theory " to be confronted with mumbo-jumbo

like

" intelligent design " , but, like gravity, an inevitable feature of the

universe we inhabit.

 

What is at issue is not the fact of evolution, but its mechanisms. As

Eva Jablonka and Marion Lamb are at pains to remind us in this important

book, Darwin himself, a naturalist and consummate observer of living

organisms, was a pluralist about such mechanisms, even embracing a

version of Lamarckism - the inheritance of acquired characteristics.

Conventional historiography ascribes this to his being unaware of

Mendel's

discoveries and so of genes. If he had known, he would have been as

monolithic as have become his ultra-Darwinist followers. For them,

evolution

is about one thing only - genes, aka DNA.

The tendency to such reductionism set in as far back as the 1930s, when

evolution ceased to be defined in term of changes in organisms

(phenotypes, such as the shape of the beaks amongst the Galapagos

finches that

Darwin studied) and instead was seen as " the rate of change of gene

frequencies in a population " . Francis Crick formulated what he called

" the

central dogma " of molecular biology as the one-way flow of information

from gene (DNA) to organism.

 

But it was Richard Dawkins above all who captured the sense of

ultra-Darwinism when he divided the living world between replicators -

structures which can be accurately copied, like DNA molecules - and

vehicles,

the " lumbering robots " whose function is to enable that copying.

 

Despite the attractions of its doctrinal simplicity, important strands

of biological thinking have never accepted this genocentric view of the

world, and many doubt that Darwin would have either. The late Stephen

Jay Gould, for example, insisted that selection acted at multiple

levels, not just on individual genes, but on populations of organisms and

indeed on species and ecosystems as a whole. In this perspective,

Dawkins'

lumbering robots become players in their own destiny.

 

An even more fundamental attack has come from researchers interested in

how organisms develop. To appreciate the importance of this, think

about the fact that humans are just under 99% genetically identical to

chimpanzees, yet no one would confuse the two. The origin of the

differences between the two phenotypes lies in their development,

which in turn

depends on which genes are switched on or off at any time - a process

regulated by the cellular environment in which the genes are embedded.

Genes do not exist in isolation, but as part of a web of interactions

extending in time as well as space.

 

Indeed, as more and more is learned about the complexities of these

processes, the concept of " the gene " as a reified DNA sequence tends to

dissolve. What exists, as one molecular biologist put it, is not a set of

discrete genes, but an entire genome. And what evolves is neither a set

of genes nor a given static phenotype, but a developmental system,

embedded as that system is in an even broader web of interactions with

its

fluctuating environment - the famous " tangled bank " of hedgerow species

that Darwin invokes in the closing paragraph of The Origin. Jablonka

and Lamb's book makes the case for this much richer view of evolution by

going both back to Darwin and forward to the latest findings of

molecular and behavioural biology. What matters, they insist, is not

genes per

se but heritable variation - variations that are transmitted, by

whatever means, from one generation to the next.

 

There are, they suggest, four levels at which such variation can occur.

The first is unexceptional: the shuffling of DNA in sexual

reproduction, which mixes variants from both parents, coupled with

mutations -

random changes in the DNA sequence. A second major source is not genetic

but epigenetic - it depends on changes that occur in the " meaning " of

given strands of DNA. Molecular biologists are discovering an increasing

number of esoteric ways that DNA, or the proteins that surround it and

ensure its orderly translation, are chemically modified during

development. Such modifications, which profoundly alter how an organism

develops, can, just like copies of DNA, be transmitted during

reproduction, and

in due course can feed back to modify the sequence of DNA itself.

 

A third dimension of evolution is one whose study Jablonka has made

particularly her own - the inheritance of behavioural traditions. Rabbit

mothers who feed on juniper berries transmit to their offspring a

preference for such food, an inheritance stable across generations. In

the

days when milk was delivered in bottles to our doorsteps, blue tits

learned to peck open the foil tops to drink the cream, a tradition

acquired

and passed on, by social learning, from generation to generation but

now presumably lost because, in an environment of Tetra Paks, it is no

longer an adaptive form of behaviour.

 

The authors' final dimension, a uniquely human one, is symbolic

inheritance, the traditions we learn and pass on not by subtle

odour-based

cues in our mother's milk or faeces, or by direct imitation of our elders

or peers, but through our capacity for language, and culture, our

representations of how to behave, communicated by speech and writing.

 

The treatment of these higher levels is important, as the authors

carefully distinguish their approach from the banalities of evolutionary

psychology, of " memes " , and even from Chomskyian ideas of universal

grammar.

 

The slowest of all these forms of evolutionary change is that based on

DNA, and there is a tendency to dismiss the others as all dependent " in

the last analysis " on genes. Jablonka and Lamb vigorously rebut this.

Rather, they insist, there are constant interactions between the levels

- epigenetic, behavioural and even symbolic inheritance mechanisms also

produce selection pressures on DNA-based inheritance and can, in some

cases, even help direct DNA changes themselves - so " evolving

evolution " .

 

As the authors admit, some non-biologists will find the more molecular

chapters heavy going - they advise readers to hum the molecules rather

as we have been taught to hum the equations in books by Hawking or

Penrose. And in the best philosophical tradition, they enliven their text

by thought experiments and dialogue with a sceptical enquirer, one

IM-Ifcha Mistraba, Aramaic, they say, for " the opposite conjecture " .

But the

book - especially when dealing with the higher level evolutionary

dimensions and the dialogues with IM - reads easily. It would be nice to

think that it would dent the appeal of simplistic selfish genery. There

is, after all, as Darwin said, " grandeur in that view of life " - but I'm

not holding my breath.

 

· Steven Rose's latest book, The 21st Century Brain, was published by

Cape in March.

 

 

 

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