Origin of human genus may have occurred by chance Paper challenges the claim that the genus Homo originated in response to environmental changes

 An often cited claim that humans, who are  smarter and more technologically advanced than their ancestors,  originated in response to climate change is challenged in a new report  by a Center for the Advanced Study of Human Paleobiology researcher at  George Washington University. 

Many scientists have argued that an influx, described as a "pulse,"  of new animal species appear 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, W.  Andrew Barr, a visiting assistant professor of anthropology, published a  report that says it's possible the pulse of new species could have  occurred by chance and might not be directly related to climate change. 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. Dr. 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. Dr. Barr's findings mean scientists may need to rethink  widely-accepted ideas about why human ancestors became smarter and more  sophisticated. "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," Dr. Barr said. "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." He compared the pattern to flipping a coin. If you flip a coin 100  times, you would expect to record 50 heads and 50 tails. However, if you  are only looking at 10 coin flips, you could see a greater imbalance,  instead recording seven heads and only three tails. This would even out  over time, but in the short-run, you could see clusters of these  independent coin flips, he said. Similarly, fluctuations in turnover in Dr. Barr's model are pronounced, but are caused purely by random processes. "The idea the 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," Dr. Barr  said. This research challenges scientists to be careful about the stories  they tell about the history of human adaption, Dr. Barr said. Traits  that make humans different from our ancestors, like larger brains and  greater technological sophistication, could have arisen for a variety of  reasons, he said. "We can sit in the present and tell stories of the past that make  sense of our modern day adaptations," he said. "But these could have  evolved for reasons we don't know." The report, "Signal or noise? A null model method for evaluating the significance of turnover pulses," was published July 31. 

source: https://www.sciencedaily.com/releases/2017/08/170804100410.htm