Questioning the survival of the fittest

Darwin’s theory of evolution and the survival of the fittest may not be correct suggests a new study which shows biodiversity may evolve where it was previously thought impossible.

The work by the Universities of Bath and Exeter, with collaborators at San Diego State University, represents a new approach to studying evolution and may lead to a better understanding of the diversity of bacteria that cause human diseases.

For any given niche, there should be a ‘best’ or fittest species, one that will eventually dominate and exclude all others. Ecologists call this the ‘competitive exclusion principle’ and it predicts that complex environments are necessary to support complex diverse populations.

This principle had been tested by microbiologists who constructed very simple environments in test tubes in the lab to see what happens after hundreds of generations of bacterial evolution – about 3,000 years in human terms said Exeter’s Professor Robert Beardsmore.

“It had been believed that the genome of only the fittest bacteria would be left, but that wasn’t their finding,” Beardsmore said. “The experiments generated lots of unexpected genetic diversity.”

Key to the new principle is the amount of food available to the bacteria say the scientists.

“Give them abundant food and they use it inefficiently,” he said. “When we combine this with the notion that organisms with different food-utilising strategies are also affected in different ways by genetic mutations, then we discover as new principle, one in which both fit and unfit coexist indefinitely,” said Professor Laurence Hurst from the University of Bath.

The fit use their food well but are resilient to mutations, while the less fit are maintained by their resilience to mutation said Dr Ivana Gudelj from Exeter.
“If there is a low mutation rate, survival of the fittest rules, but if not, lots of diversity can be maintained,” Gudelj said. “Rather nicely, the numbers needed for the principle to work accord with those enigmatic experiments on bacteria. Their mutation rate seems to be high enough for both fit and unfit to be maintained.”

“Opposing food utilisation strategies could coexist in complex environments,” said Dr David Lipson of San Diego State. “Trade-offs like the one we studied between growth rate and efficiency, can lead to a stable diversity in the simplest possible of environments.”