Did humans evolve by chance?

Washington: A new study says that origin of human genus could have occurred by chance and might not be directly related to climate change, as commonly believed.

Many scientists have argued that an influx, described as a "pulse", of new animal species appears in the African fossil record between 2.8 and 2.5 million years ago, including our own genus Homo.

Experts believe it takes a broad-scale event like global climate change to spark the origination of so many diverse new species. However, the new study, published in the journal Paleobiology, says it is possible the pulse of new species could have occurred by chance.

"The idea that our genus originated more than 2.5 million years ago as part of a turnover pulse in direct response to climate change has a deep history in paleonthropology," said Andrew Barr from George Washington University.

"My study shows that the magnitude of that pulse could be caused by random fluctuations in speciation rates. One implication is that we may need to broaden our search for why our genus arose at that time and place," Barr said. It is generally accepted that when major environmental changes occur, some species will go extinct and others will originate, which can create a cluster or pulse of new species in the fossil record.

However, there is not a set definition of what is considered a pulse, so experts have disagreed about which clusters constitute meaningful events and which can be explained as random fluctuations.

Barr used computer simulation to model what the fossil record might look like over time in the absence of any climate change and found clusters of species originations that were of similar magnitude to the clusters observed in the fossil record.

This means random patterns are likely under-credited for their role in speciation fluctuation, he said.The findings mean scientists may need to rethink widely-accepted ideas about why human ancestors became smarter and more sophisticated.