Washington - Life, as it evolves, becomes increasingly complex and rarely less so, a study of evolution by British and Canadian researchers has found.
In the study out on Monday researchers looked back 550 million years in the fossil catalogue from today, checking several evolutionary branches of the crustacean family tree to see where animals evolved that became simpler than their ancestors.
But instead they found organisms that developed increasingly complicated structures and characteristics.
"If you start with the simplest possible animal body, then there's only one direction to evolve in, you have to become more complex," said Dr Matthew Wills from the Department of Biology & Biochemistry at the University of Bath who worked with colleagues Sarah Adamowicz from the University of Waterloo, Canada, and Andy Purvis from Imperial College London.
"Sooner or later, however, you reach a level of complexity where it's possible to go backwards and become simpler again," he said.
"What's astonishing is that hardly any crustaceans have taken this backwards route," added Wills. "Instead, almost all branches have evolved in the same direction, becoming more complex in parallel.
"This is the nearest thing to a pervasive evolutionary rule that's been found."
Adamowicz noted that "looking at many independent branches is similar to viewing multiple repeated runs of the tape of evolution.
"Our results apply to a group of animals with bodies made of repeated units. We must not forget that bacteria, very simple organisms, are among the most successful living things.
"Therefore, the trend towards complexity is compelling but does not describe the history of all life," she said.
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Hmmm... not sure how true this is, I deal with people on a daily basis that have without a doubt evolved backwards