Human scientists have attributed the rise of our ancestors—the genus Homo—to climate change in Eastern Africa. The colder and more arid and changeable weather patterns in Eastern Africa favored bigger brains and better smarts, the theory has traditionally held.

But a computer simulation of evolution appears to indicate that the influx of hominids starting about 2.8 million years ago could instead have been the product of random chance, according to a new study in the journal Paleobiology.

“The idea that the origin of Homo is part of a climate-caused turnover pulse doesn’t really bear out when you carefully look at the evidence and compare it against other possible explanations,” said W. Andrew Barr, an anthropologist at George Washington University, who authored the paper.

A series of 1,000 hypothetical fossil records were created through a computer simulation. Those models were made without the factor of climate change included.

The clusters of species appeared to indicate that the long timeline and the statistical probabilities of adaptation were the main drivers for the degree of variation, rates of extinction and genesis of species.

The takeaway: climate change during the Plio-Pleistocene may not have played the pivotal role in human evolution that has previously been believed, Barr writes.

“The results of this study argue for extreme caution in attempting to detect meaningful turnover pulses in data sets that comprise relatively few taxa per time bin,” they write. “Such data sets are particularly prone to type I errors and may lead to misleading conclusions about the presence of biologically meaningful pulses of turnover.”

The human evolutionary tree continues to get more twists and tangles in its branches. Two years ago, researchers announced they had identified a new species called Homo naledi which apparently had toolmaking ability and human-like traits, but which also shared some Australopithecus features