Findings: Chemically constrained

A chemist's view of evolution has revealed the guiding hand that gives Richard Dawkins's blind watchmaker a sense of direction, writes Steve Farrar.

Robert Williams, senior research fellow at Wadham College, Oxford, and Joio FraNosto da Silva, professor of chemistry at the Instituto Superior Tecnico, Lisbon, suggest that the changing chemical environment has constrained development of life in such a way as to send it on a fixed trajectory.

They argue that if life exists on other earth-like planets elsewhere in the universe, its evolution would have been directed in the same manner.

Life forms first evolved on earth with an internal chemistry associated with 15 to 20 readily available elements found in the primordial oceans and the atmosphere of the earth. These set the limits on basic biological systems.

But over time, the first single-cell organisms were able to alter the chemical environment they came from through their production of oxygen as a waste product. This changed the make-up of the atmosphere and, through oxidation, made available more elements that had previously been "locked away" in unusable forms.

Many of the new chemicals were damaging to the interior of the cells. But organisms that were able to utilise them - many as catalysts - gained an advantage over their competitors because of their ability to extract the elements and use energy from the environment.

Professor Williams and Professor FraNosto da Silva said this produced an evolutionary pressure for more complex internal organisation that could keep clashing chemistries apart within a single organism.

In this way, simple prokaryotes including bacteria were followed by the more complex eukaryotes whose membranes divided the cytoplasm into separate compartments.

As the environment became increasingly oxidative, multicellular life forms evolved where different cells communicated with one another. Then came animals, with their ability to manipulate the outside world, and ultimately humankind, with its industrial production of a host of new chemicals. "This means that man must take great care over the environment," Professor Williams said.

The findings will appear in the Journal of Theoretical Biology .