But the findings suggest the presence of a system of innate responses, said Hitoshi Sakano, from the University of Tokyo, whose team bred the strain of mice.

He added that the mutant mice lacked innate responses to 'aversive odorants' - the smell of fear - even though they were capable of detecting-them. But they could still be conditioned for aversion.

Humans could have a similar system for discerning fear, the researchers said in their report in the journal Nature.

The findings follow the announcement last week that scientists in Ohio have created a 'super mouse' that can run 6km (3.7 miles) without stopping.

The mouse has a longer life expectancy, can also breed for much longer than normal mice and never puts on weight, despite eating 60 per cent more than average.