Evolutionary biologists say crossbreeding between species is far more common than previously thought, making a nonsense of the idea of discrete evolutionary branches

Charles Darwin's "tree of life", which shows how species are related through evolutionary history, is wrong and needs to be replaced, according to leading scientists.

The great naturalist first sketched how species might evolve along branches of an imaginary tree in 1837, an idea that quickly came to symbolise the theory of evolution by natural selection.

But modern genetics has revealed that representing evolutionary history as a tree is misleading, with scientists saying a more realistic way to represent the origins and inter-relatedness of species would be an impenetrable thicket. Darwin himself also wrote about evolution and ecosystems as a "tangled bank".

"We have no evidence at all that the tree of life is a reality," Eric Bapteste, an evolutionary biologist at the Pierre and Marie Curie University in Paris, told New Scientist magazine.

Genetic tests on bacteria, plants and animals increasingly reveal that different species crossbreed more than originally thought, meaning that instead of genes simply being passed down individual branches of the tree of life, they are also transferred between species on different evolutionary paths. The result is a messier and more tangled "web of life".

Microbes swap genetic material so promiscuously it can be hard to tell one type from another, but animals regularly crossbreed too - as do plants - and the offspring can be fertile. According to some estimates, 10 per cent of animals regularly form hybrids by breeding with other species.

Last year, scientists at the University of Texas at Arlington found a strange chunk of DNA in the genetic make-up of eight animals, including the mouse, rat and the African clawed frog. The same chunk is missing from chickens, elephants and humans, suggesting it must have become wedged into the genomes of some animals by crossbreeding.

The findings mean that to link species by Darwin's evolutionary branches is an oversimplification. "The tree of life is being politely buried," said Michael Rose, an evolutionary biologist at the University of California, Irvine. "What's less accepted is that our whole fundamental view of biology needs to change."