TOUGH BEAT FOR OLE CHUCKIE D:

The paper relies on modeling using the genomes of 290 living people from southern, eastern and western Africa. The findings suggest that modern humans descended from at least two groups of ancient humans that were closely related and mixed genes on occasion, writes Live Science's Charles Q. Choi.

"There is no single birthplace," Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute for Geoanthropology in Germany who did not contribute to the study, tells the New York Times' Carl Zimmer. "It really puts a nail in the coffin of that idea."

Rather than envisioning human evolution as a tree--with a single stem that splits into disconnected branches--the researchers describe ancestral human populations as intertwining stems, writes Nature News' Jude Coleman.

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