27 March 2011
notion that only the fittest survive has been called into
question by new research
published today (27 March 2011) in Nature.
A collaboration between the Universities of Bath and Exeter, along
with a group from San Diego State University in the US, challenges
our current understanding of evolution by showing that biodiversity
may evolve where previously thought impossible.
The work represents a new approach to studying evolution that may
eventually lead to a better understanding of the diversity of
bacteria that cause human diseases.
Conventional wisdom has it that for any given niche there should be
a best species, the fittest, that will eventually dominate to
exclude all others.
This is the principle of survival of the fittest. Ecologists often
call this idea the 'competitive exclusion principle' and it predicts
that complex environments are needed to support complex, diverse
Professor Robert Beardmore, from the University of Exeter,
“Microbiologists have tested this
principle by constructing very simple environments in the lab to
see what happens after hundreds of generations of bacterial
evolution, about 3,000 years in human terms.
“It had been believed that the genome of only the fittest
bacteria would be left, but that wasn’t their finding. The
experiments generated lots of unexpected genetic diversity.”
This test tube biodiversity proved
controversial when first observed and had been explained away with
claims that insufficient time had been allowed to pass for a clear
winner to emerge.
The new research shows the experiments were not anomalies.
Professor Laurence Hurst, of the University of Bath, said:
“Key to the new understanding is the
realization that the amount of energy organisms squeeze out of
their food depends on how much food they have.
“Give them abundant food and they use it inefficiently. When we
combine this with the notion that organisms with different
food-utilizing strategies are also affected in different ways by
genetic mutations, then we discover a new principle, one in
which both the fit and the unfit coexist indefinitely.”
Dr Ivana Gudelj, also from the
University of Exeter, said:
“The fit use food well but they
aren’t resilient to mutations, whereas the less efficient, unfit
consumers are maintained by their resilience to mutation.
“If there’s a low mutation rate, survival of the fittest rules,
but if not, lots of diversity can be maintained.
“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
Dr. David Lipson of San Diego
State University, concluded:
“Earlier work showed that opposing
food utilization strategies could coexist in complex
environments, but this is the first explanation of how
trade-offs, like the one we studied between growth rate and
efficiency, can lead to stable diversity in the simplest
possible of environments.”