Did different species of early humans interbreed and produce offspring of mixed ancestry? Recent genetic studies suggest that Neanderthals may have bred with anatomically modern humans tens of thousands of years ago in the Middle East, contributing to the modern human gene pool. But the findings are not universally accepted, and the fossil record has not helped to clarify the role of interbreeding, which is also known as hybridization.
Now a University of Michigan-led study of interbreeding between two species of modern-day howler monkeys in Mexico is shedding light on why it's so difficult to confirm instances of hybridization among primates - including early humans - by relying on fossil remains.
One of the authors of the study, published online Dec. 7, 2012 in the American Journal of Physical Anthropology, is Dr. Liliana Cortés-Ortiz, an evolutionary biologist and primatologist and an EEB assistant research scientist at the Museum of Zoology. The study is based on analyses of genetic and morphological data collected from live-captured monkeys over the past decade. Morphology is the branch of biology that deals with the form and structure of animals and plants.
The two primate species in the study, mantled howler monkeys and black howler monkeys, diverged about 3 million years ago and differ in many respects, including behavior, appearance and the number of chromosomes they possess. Each occupies a unique geographical distribution except for the state of Tabasco in southeastern Mexico, where they coexist and interbreed in what's known as a hybrid zone.
The researchers found that individuals of mixed ancestry who share most of their genome with one of the two species are physically indistinguishable from the pure individuals of that species.
"The implications of these results are that physical features are not always reliable for identifying individuals of hybrid ancestry. Therefore, it is possible that hybridization has been underestimated in the human fossil record," said Cortés-Ortiz.
The paper was widely covered in the media, including the Spanish language news outlets. Previously on the U-M Gateway
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