Dr Adamowicz said: Previous researchers noticed increasing morphological complexity in the fossil record, but this pattern can occur due to the chance origination of a few new types of animals.
Our study uses information about the inter-relatedness of different animal groups the Tree of Life to demonstrate that complexity has evolved numerous times independently.
Like all arthropods, crustaceans bodies are built up of repeating segments. In the simplest crustaceans, the segments are quite similar - one after the other. In the most complex, such as shrimps and lobsters, almost every segment is different, bearing antennae, jaws, claws, walking legs, paddles and gills.
The American biologist Leigh Van Valen coined the phrase Red Queen for the evolutionary arms race phenomenon. In Through the Looking-Glass Lewis Carrolls Red Queen advises Alice that: It takes all the running you can do, to keep in the same place.
Those crustacean groups going extinct tended to be less complex than the others around at the time, said Dr Wills.
Theres even a link between average complexity within a group and the number of species alive today.
All organisms have a common ancestor, so that every living species is part of a giant family tree of life.
Dr Adamowicz added: With a few exceptions, once branches of the tree have separated they continue to evolve independently.
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.
|Contact: Andrew McLaughlin|
University of Bath