While previous studies have shown babies in their first six months react positively to attractive features, this is the first evidence infants make "friends or foe" decisions.

The findings suggest some social traits are present at birth and not simply learned.

The study by researchers at Yale University involved showing groups of six-month and ten-month-old babies toys with "good", "neutral" or "bad" traits and recording which ones they preferred.

In the first experiment, babies were shown "the climber", a wooden toy with large, glued-on eyes which rested at the bottom of a hill before repeatedly trying and failing to climb it.

The climber was then helped to the top by a triangular character pushing from behind, or hindered by a square character pushing down the hill.

Fourteen of the 16 ten-month-olds and all 12 of the six-month-olds preferred the triangular helper. A second experiment ruled out the possibility the infants were merely responding to the direction in which the figures were moving.

In a third experiment, infants of both ages preferred a helper to a neutral party, and a neutral party over one who hindered.

The researchers, led by psychologist Professor Karen Wynn, describe their finding today in the journal Nature.

"This supports the view that our ability to evaluate people is a biological adaptation – universal and unlearned," she said.

"The presence of social evaluation so early in infancy suggests that assessing individuals by the nature of their interactions with others is central to processing the social world, both evolutionarily and developmentally."

In the past, this ability would have played an essential role in activities such as group hunting, food sharing and warfare, said the scientists.

Dr Mary Brown, a lecturer in organisational behaviour at Robert Gordon University in Aberdeen, said the study could challenge the prevailing view of "survival of the fittest".

She said: "If this study is replicated it could provide a counterweight to arguments that we are all programmed to do whatever it takes to ensure our gene pool survives.

"We are often presented with ideas of ’social Darwinism’ but these results could show collaborative behaviour is part of our nature as much as competitiveness."

But Dr Michael Brady, of the department of philosophy at the University of Glasgow, said he doubted that babies had sophisticated moral capabilities.

"I’d be reticent to conclude that the experiment indicates our ability to evaluate people is universal and unlearned.

"I’m not sure that responses to wooden blocks constitute evidence of "social evolution" either, unless we have evidence that the babies somehow take these blocks to be creatures with interests."

The average baby is smarter than you think.

Lots of "under the radar" work goes on before babies utter their first word.

While it may seem it has taken a year to learn a word, Professor Bob McMurray, psychologist at Iowa University, said babies learn in a "parallel universe" before going public.

Babies might look at you blankly but they are processing every change in the shape and rhythm of your mouth and face.

Infants as young as four months know when someone is speaking to them in a foreign language and pay more attention to facial expressions. Babies have been shown to recognise their mother’s muffled language as it penetrates the womb. When played recordings of their mother talking to another woman they suck harder on a dummy when they hear their mother’s voice.