When it comes to counting, a remote Amazonian tribespeople have been found to be lost for words.
Researchers discovered the Piraha tribe of Brazil, with a population of 200, have no words beyond one, two and many.
The word for "one" can also mean "a few", while "two" can also be used to refer to "not many".
Peter Gordon of Columbia University in New York said their skill levels were similar to those of pre-linguistic infants, monkeys, birds and rodents.
He reported in the journal Science that he set the tribe simple numerical matching challenges, and they clearly understood what was asked of them.
"In all of these matching experiments, participants responded with relatively good accuracy with up to two or three items, but performance deteriorated considerably beyond that up to eight to 10 items," he wrote.
Dr Gordon added that not only could they not count, they also could not draw.
"Producing simple straight lines was accomplished only with great effort and concentration, accompanied by heavy sighs and groans."
The tiny tribe live in groups of 10 to 20 along the banks of the Maici River in the Lowland Amazon region of Brazil.
Dr Gordon said they live a hunter-gatherer existence and reject any assimilation into mainstream Brazilian culture.
He added that the tribe use the same pronoun for "he" and "they" and standard quantifiers such as "more", "several" and "all" do not exist in their language.
"The results of these studies show that the Piraha's impoverished counting system truly limits their ability to enumerate exact quantities when set sizes exceed two or three items," he wrote.
"For tasks that required cognitive processing, performance deteriorated even on set sizes smaller than three."
The findings lend support to a theory that language can affect thinking.
Linguist Benjamin Lee Whorf suggested in the 1930s that language could determine the nature and content of thought.