A controversial theory that humans evolved from amphibious apes has won new support.
The aquatic ape theory, whose supporters include David Attenborough, suggests that apes emerged from the water, lost their fur, started to walk upright and then developed big brains.
While it has been treated with scorn by some scientists since it first emerged 50 years ago, it is backed by a committed group of academics, including Sir David.
The group will hold a major London conference next week featuring several speakers who will voice support for the theory.
Peter Rhys Evans is one of the organisers of Human Evolution: Past, Present and Future.
He told the Observer that humans are very different from other apes, as we lack fur, walk upright, have big brains and subcutaneous fat and have a descended larynx - which is common among aquatic animals.
According to evolutionary theories, these features appeared at separate times, for different reasons.
But the aquatic ape theory says they appeared because our ancestors decided to live in or near water for millions of years.
British biologist Sir Alister Hardy first theorised that we were descended from aquatic apes.
He wrote that apes came down from the trees to live in the food rich creeks, river and seas.
He said they evolved to become upright as they tried to keep their heads above water, and lost their hair. They developed fat to keep warm in the water.
Rhys Evans, an expert on head and neck physiology at the Royal Marsden hospital, London, told the Observer that humans have large sinuses. He argues the spaces in the cranium between cheeks, noses and foreheads, acted as buoyancy aids that helped keep our heads above water.
Others have dismissed the theory.
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Professor Chris Stringer of the Natural History Museum, London, said that while wading through water was as good as any explanation for our upright gait, the 'whole aquatic ape package includes attributes that appeared at very different times in our evolution.'
Supporters of the theory say humans developed large brains thanks to Docosahexaenoic acid (DHA) - an omega-3 fatty acid found in seafood
He said: 'If they were all the result of our lives in watery environments, we would have to have spent millions of years there and there is no evidence for this - not to mention like crocodiles and other creatures would have made the water a very dangerous place.'
Supporters of the theory also argue that human brain biochemistry could also help prove the link.
Docosahexaenoic acid (DHA) - an omega-3 fatty acid found in seafood - boosts brain growth in mammals.
Dr Michael Crawford, of Imperial College London, said without a high DHA diet from seafood we could not have developed big brains.
He said the world's sources of DHA – fish stocks – are threatened, with 'crucial consequences for our species.'He added: 'Without plentiful DHA, we face a future of increased mental illness and intellectual deterioration. We need to face up to that urgently. That is the real lesson of the aquatic ape theory.'