Imagine a life without numbers. It would be tricky to know if your salary has been paid or if a shopkeeper has short-changed you.
But one tribe living in the Amazon rainforest does just fine without them.
The Piraha people have words to express quantities such as 'some' and 'more' but not individual numbers.
The 300-strong group use one term to quantify things between one and four and another for five or above, researchers found. 'It is often assumed counting is an innate part of human cognition,' said Prof Edward Gibson, of US university MIT.
'This group could learn but it's not useful in their culture, so they've never picked it up.'
The research follows a similar discovery in 2004 by a team of equally intrepid linguists from Columbia University.
They believed the same tribe had words for 'one', 'two' and 'many' only and linked the skill level involved to that of infants, rodents, monkeys and birds.
As hunter-gatherers who rejected any assimilation into mainstream Brazilian culture, they appeared to have no need for a counting system.
But it was also found that they lacked another commonplace skill – drawing.
'Producing simple straight lines was accomplished only with great effort and concentration, accompanied by heavy sighs and groans,' Dr Peter Gordon told journal Science.