Relative would have been 5ft 9 inches, compared to H. habilis, at 3ft tall

A 1.85 million-year-old bone from the little finger of a human ancestor has revealed the oldest 'modern' hand ever found.

The discovery in Olduvai Gorge pushes back in time a key step in our evolution from tree-climbing foragers to tool-wielding hunters, scientists say.

It also hints at the existence of a larger, more human-like creature than others known to have lived at that time in the same region - one of the hotspots of human origin - in modern-day Tanzania.

A tiny, 1.85 million-year-old bone from the little finger of a human ancestor has revealed the oldest 'modern' hand ever found. The discovery of the bone in Olduvai Gorge pushes back in time a key step in our evolution from tree-climbing foragers to tool-wielding hunters

The hand is one of the critical features distinguishing humans, and even a 3.6 cm(1.5-inch), two-million-year-old fragment can reveal a lot about body type and behaviour.

The shape of our forebears' hands was both a reflection of their stage of evolution, explained lead author Manuel Dominguez-Rodrigo, a researcher at the Institute of Evolution in Africa in Madrid.

'Our hand evolved to allow us a variety of grips and enough gripping power to allow us the widest range of manipulation observed in any primate,' he explained.

'It is this manipulation capability that interacted with our brains to develop our intelligence, mainly through the invention and use of tools.'

The hand is one of the critical features distinguishing humans, and even a 3.6 cm(1.5-inch), two-million-year-old fragment can reveal a lot about body type and behaviour. Pictured are rotating views of the little finger bone believed to be the first 'modern hand' ever found

THE COMPLEX EVOLUTION OF MAN 55 million years ago - First primitive primates evolve 15 million years ago - Hominidae (great apes) evolve from the ancestors of the gibbon 8 million years ago - First gorillas evolve. Later, chimp and human lineages diverge 5.5 million years ago - Ardipithecus, early 'proto-human' shares traits with chimps and gorillas 4 million years ago - Australopithecines appeared. They had brains no larger than a chimpanzee's 2.8 million years ago - LD 350-1 appeared and may be the first of the Homo family 2.7 million years ago - Paranthropus, lived in woods and had massive jaws for chewing 2.3 million years ago - Homo habalis first thought to have appeared in Africa 1.85 million years ago - First 'modern' hand emerges 1.8 million years ago - Homo ergaster begins to appear in fossil record 1.6 million years ago - Hand axes become the first major technological innovation 800,000 years ago - Early humans control fire and create hearths. Brain size increases rapidly 400,000 years ago - Neanderthals first begin to appear and spread across Europe and Asia 200,000 years ago - Homo sapiens - modern humans - appear in Africa 40,0000 years ago - Modern humans reach Europe Advertisement

If the bone is proportional to a modern-human-like body, the unknown ancestors it would have belonged to would have been 5 feet 9 inches, compared to H. habilis, who was just over 3 feet tall.

The discovery pushes the earliest 'modern' hand back by around 400,000 years.

What scientists call 'modern human-like' hand anatomy has several defining characteristics.

One is a longer thumb, allowing us to grip more precisely and to open our hands more fully.

Another is the straightening of our phalanges, the general name given to the three bones found in each finger.

Curved phalanges were adapted for climbing trees and swinging from branches.

'A modern-like hand in the past would tell us when humans became fully terrestrial and when and how efficiently our ancestors used tools,' Dominguez-Rodrigo said.

That transition happened in two main stages.

After the earliest hominins - which includes all members of the Homo genus - began walking on two legs some six million years ago, the hand evolved a longer thumb.

But the fingers remained curved, suggesting that trees remained part of their habitat.

This 'double locomotion' - on the ground, through the trees - remained the norm for another four million years.

As our ancestors abandoned their arboral perches, their fingers began to straighten, opening the way for the creation and use of tools.

'Hands were freed from locomotion in trees so that they could become strictly specialised in manipulation,' said Dominguez-Rodrigo. 'This is where our discovery fills a gap.'

The earliest confirmed stone tools date from about 2.6 million years ago.

The find, reported in Nature Communications, will fuel ongoing debate as to which of our distant relatives might have been the first to make stone implements and weapons.

'Our discovery not only shows that a creature' - dubbed OH 86 - 'with a modern-looking hand existed 1.85 million years ago, it also shows that OH 86 was bigger sized than any other prior and contemporary hominin,' said Dominguez-Rodrigo.

Archeological evidence from the Olduvai Gorge in Tanzania, where the little finger bone was found, shows that size mattered.

The find, reported in Nature Communications, will fuel ongoing debate as to which of our distant relatives might have been the first to make stone implements and weapons. Pictured are researchers excavating the fossiliferous layer at the Olduvai Gorge

Fossils reveal that early human ancestors hauled the carcasses of big animals, sometimes weighing hundreds of kilos.

EVOLUTION OF THE HUMAN HAND After the earliest hominins - which includes all members of the Homo genus - began walking on two legs some six million years ago, the hand evolved a longer thumb. But the fingers remained curved, suggesting that trees remained part of their habitat. This 'double locomotion' - on the ground, through the trees - remained the norm for another four million years. As our ancestors abandoned their arboral perches, their fingers began to straighten, opening the way for the creation and use of tools. 'Hands were freed from locomotion in trees so that they could become strictly specialised in manipulation,' said Dominguez-Rodrigo. 'This is where our discovery fills a gap.' The earliest confirmed stone tools date from about 2.6 million years ago. Fossils from the earliest modern hand date back to 1.85 million years ago. Advertisement

'I always had trouble understanding how Homo habilis - barely taller than one metre (3ft) - could efficiently hunt animals that big,' Dominguez-Rodrigo said.

The existence of a bigger, more modern-looking hominin would help explain this puzzle.

Other experts not involved in the study agreed.

'It brings support to those who challenge the view that Homo habilis was the maker of the stone artifacts becoming abundant in layers of this time period,' commented Jean-Jacques Hublin, director of the department of human evolution at the Max Planck Institute for Evolutionary Anthropology.

At the same time, Hublin and others challenged the broad conclusions reached on the basis of such slim evidence.

'One single bone from a pinkie finger does not imply a whole modern human-like skeleton,' Hublin said.

Another leader in the field, Tracy Kivell of the School of Anthropology and Conservation at the University of Kent, was even more sceptical.

'This single bone tells us nothing about what the rest of the hand looked like, let alone what the rest of the skeleton looked like,' she told AFP by mail.

'If recent, more complete hominin fossil discoveries have taught us anything, it's that strange combinations of more derived human-like features and more primitive australopith-like features throughout the skeleton are likely the rule, rather than the exception, especially at this time period.'