London, March 27 (IANS): Scientists have found evidence that contradicts the dominant theory of our evolution - that our genus, Homo, evolved from small bodied early humans to become the taller, heavier and longer legged Homo erectus that was able to migrate beyond Africa and colonise Eurasia.

The new study, published in the Journal of Human Evolution, says the main increase in body size occurred tens of thousands of years after Homo erectus left Africa.

Basically every textbook on human evolution gives the perspective that one lineage of humans evolved larger bodies before spreading beyond Africa.

"But the evidence for this story about our origins and the dispersal out of Africa just no longer really fits," said study co-author Jay Stock from the University of Cambridge.

Comparing measurements of fossils from sites in Kenya, Tanzania, South Africa and Georgia, the researchers found that there was a significant regional variation in the size of early humans during the Pleistocene era.

Some groups, such as those who lived in South African caves, averaged 4.8 feet in height.

Some of those found in Kenya's Koobi Fora region would have stood at almost six feet, comparable to the average of today's male population in Britain.

The first clues came from the site of Dmanisi in Georgia where fossils of really small bodied people date to 1.77 million years ago.

"This has been known for several years, but we now know that consistently larger body size evolved in Eastern Africa 1.7 million years ago, in the Koobi Fora region of Kenya," Stock added.

According to Manuel Will, a co-author of the study from the Tubingen University in Germany, "the evolution of larger bodies and longer legs can thus no longer be assumed to be the main driving factor behind the earliest excursions of our genus to Eurasia."

"If someone asked you 'are modern humans six feet tall and 70kg?' you'd say 'well some are, but many people aren't', and what we're starting to show is that this diversification happened really early in human evolution," said Stock.

The study is the first in 20 years to compare the body size of the humans who shared the earth with mammoths and sabre-toothed cats between 2.5 and 1.5 million years ago.