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Scientists at the University of Liverpool have provided the first
experimental evidence that shows that evolution is driven most
powerfully by interactions between species, rather than adaptation to
The team observed viruses as they evolved over hundreds of
generations to infect bacteria. They found that when the bacteria could
evolve defences, the viruses evolved at a quicker rate and generated
greater diversity, compared to situations where the bacteria were unable
to adapt to the viral infection.
The study shows, for the first time, that the American evolutionary
biologist Leigh Van Valen was correct in his 'Red Queen Hypothesis'. The
theory, first put forward in the 1970s, was named after a passage in
Lewis Carroll's Through the Looking Glass in which the Red Queen tells
Alice, 'It takes all the running you can do to keep in the same place'.
This suggested that species were in a constant race for survival and
have to continue to evolve new ways of defending themselves throughout
Dr Steve Paterson, from the University's School of Biosciences,
explains: "Historically, it was assumed that most evolution was driven
by a need to adapt to the environment or habitat. The Red Queen
Hypothesis challenged this by pointing out that actually most natural
selection will arise from co-evolutionary interactions with other
species, not from interactions with the environment.
"This suggested that evolutionary change was created by 'tit-for-tat'
adaptations by species in constant combat. This theory is widely
accepted in the science community, but this is the first time we have
been able to show evidence of it in an experiment with living things."
Dr Michael Brockhurst said: "We used fast-evolving viruses so that we
could observe hundreds of generations of evolution. We found that for
every viral strategy of attack, the bacteria would adapt to defend
itself, which triggered an endless cycle of co-evolutionary change. We
compared this with evolution against a fixed target, by disabling the
bacteria's ability to adapt to the virus.
"These experiments showed us that co-evolutionary interactions
between species result in more genetically diverse populations, compared
to instances where the host was not able to adapt to the parasite. The
virus was also able to evolve twice as quickly when the bacteria were
allowed to evolve alongside it."
The team used high-throughput DNA sequencing technology at the Centre
for Genomic Research to sequence thousands of virus genomes. The next
stage of the research is to understand how co-evolution differs when
interacting species help, rather than harm, one another.
The research is published in Nature and was supported by
funding from the Natural Environment Research Council (NERC); the
Wellcome Trust; the European Research Council and the Leverhulme Trust.
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