British scientists conducting archaeological digs in Africa say they've found evidence early stone tool making was more sophisticated than originally thought.

At a dig site in Kenya, researchers from the University of Liverpool have found long and slender stone tools made by human ancestors at least a million years ago, nearly twice as long ago as generally thought.

While natural materials such as branches, twigs, and stems were readily available human tool makers from millions of years ago, the findings in Kenya suggest elongate forms were made out of stone by human ancestors much earlier than is usually recognized, a university release said Monday.

Archaeologist John Gowlett said he has found a number of hand axe tools that are very long and narrow.

"Some of the stone tools from Kilombe [in Kenya] and other early sites are almost two and a half times as long as broad and there is no way this can occur by accident," he said in a statement. "They must have been carefully crafted.

"Usually such slender shapes are found far later in the fine blade tools made by Homo sapiens," he said. "The [Kenya] hand-axes were made by the earlier Homo erectus."

They were probably made to carry out tasks of animal butchery or plant preparation, Gowlett said.

"They show that when the need arose early humans were capable of strikingly sophisticated behavior."

The findings are published in Philosophical Transactions of the Royal Society B.