Stephen Hawking, the acclaimed scientist and writer, reignited the debate over genetic engineering yesterday by recommending that humans change their DNA through genetic modification to keep ahead of advances in computer technology and stop intelligent machines from 'taking over the world'.

He made the remarks in an interview with the German magazine  Focus. Because technology is advancing so quickly, Hawking said, 'computers double their performance every month'. Humans, in contrast, are developing much more slowly, and so must change their DNA make-up or be left behind. 'The danger is real,' he said, 'that this computer intelligence will develop and take over the world.'

Hawking, author of the best-selling  A Brief History Of Time  and a professor of mathematics at Cambridge University, recommended 'well-aimed manipulation' of human genes. Through this humans could 'raise the complexity of... the DNA they are born with thereby improving people'. He conceded the road to genetic modification would be a long one but said: 'We should follow this road if we want biological systems to remain superior to electronic ones.'

He also advocated cyber-technology - direct links between human brains and computers. 'We must develop as quickly as possible technologies that make possible a direct connection between brain and computer, so that artificial brains contribute to human intelligence rather than opposing it.'

While scientists are excited by the huge possibilities of genetic engineering and human interaction with machines, ethicists urge caution as the experiments could go wrong.

Sue Mayer, director of policy research group Genewatch, rounded on Hawking's remarks. 'He is trying to take the debate about genetic engineering in the wrong direction,' she said. 'It is naive to think that genetic engineering will help us stay ahead of computers.'