Student - March 5, 2009

EVOLUTION IS BOTH PREDICTABLE AND RANDOM

Is evolution predictable or does the emergence of new species depend on chance? Both, concluded Wageningen biologists after an evolutionary experiment. In a new environment, chance still plays a role, but after that evolution is predictable.

‘Some people think evolution theory is soft because you can only look back and you can’t predict,’ says Dr. Arjan de Visser of the Laboratory of Genetics. ‘But we can.’

In evolutionary theory, prediction is a bone of contention. Evolutionary biologist Stephen Jay Gould claimed that if you were to do the whole of evolution all over again, completely different species would come into existence. His pupil Simon Conway Morris, however, asserted that life imposes limitations which would cause the same types of species to emerge. For example, there would be animals with four limbs, but never an animal that gets around on wheels. ‘Gould and Conway Morris are both right’, concludes De Visser. ‘At first, in the phase of adapting to a new environment, chance plays a role. Later you see that evolution repeats itself relatively often. We researched whether an enzyme that makes bacteria resistant to the old antibiotics, such as ampicillin and penicillin, can also develop resistance to the new synthetic antibiotics. We knew that it could, as this has already happened in hospitals.’

De Visser and postdoc Merijn Salverda lent evolution a bit of a hand. They copied the gene fairly sloppily – with an enzyme appropriately known as sloppy polymerase – so that there were ‘mistakes' in it. They put the ‘faulty’ copies into bacteria and then looked at which bacterium was the least vulnerable to the new antibiotic: this was the one that was the most adapted to its new environment. They got the resistance gene from that bacterium, which was once again sloppily copied. This went on until it had evolved into a gene that was resistant to the new antibiotic. This was evolution in the lab, then. And it only took three weeks.

The scientists repeated the whole series twelve times. And ten times they saw the same three mutations occurring. Touché for Simon Conway Morris: evolution sticks to well-trodden paths. But in two cases another resistant enzyme definitely came into being. ‘This happened in fact through just one mutation in the first round. So at the start, chance does play a role: a point for Stephen Jay Gould as well.’

The researchers sent their manuscript off to a publisher last week. The tide is with them – it is Darwin year after all. And last month Nature discussed experimental evolution in an article entitled The Beagle in a bottle.

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