Glenn Carter Conroy
Weatherhead Resident Scholar 1996-1997
Debating Human Origins
The publication of Reconstructing Human Origins: A Modern Synthesis (Norton
1997), a textbook for upper-level and graduate students in paleoanthropology,
coincided with author Glenn Carter Conroy's arrival at SAR for a spring semester
residency. Conroy used his time at the School to work on a planned second edition
that will incorporate molecular and genetic data that have become available
since the book went to press and add a chapter on the human fossil record in
the New World.
The recent DNA evidence Conroy has been working with relates
to a current debate over human ancestry. "DNA in mitochondria, the little
organels in our cells, are only inherited through our mothers," Conroy explained. "That
means we can trace maternal lineages back through time. Anthropologists have
been looking at the amount of diversity in mitochondrial DNA in modern human
populations. Then, on the assumption that this DNA evolves at a constant rate,
we can determine that all modern humans had a common maternal ancestor X number
of years ago."
The so-called African Eve hypothesis, based on this technique,
holds that all modern humans descended from a common ancestor who lived about
200,000 years ago in Africa. "But fossil evidence in China and Indonesia
shows that humans lived in much of the Old World as far back as one million to
one-and-a-half million years ago," Conroy noted. "If the Eve hypothesis
is correct, it would mean that a small population in Africa evolved into what
we consider Homo sapiens and then migrated out of Africa and replaced all the
other humanlike animals. In contrast, the multiregional continuity model says
that the whole Eurasian population together evolved into Homo sapiens between
one and one-and-a-half million years ago."
A textbook, of course, must present both sides of a debate. "In
this particular case," Conroy said, "I try to point out some of the
assumptions and problems in the African Eve theory and suggest that we need to
think about it rather than blindly accept it." Other debates Conroy covers
include which of the apes is closest to humans, and what he calls "the gradual
versus the jerky view" of how evolution proceeds.
Conroy's new chapter on the New World examines yet another
heated controversy, the one between those who say there were no humans in this
hemisphere before 12,000 BC and those who say there were. "Both arguments
rest almost exclusively on carbon-14 dating, and there are many problems with
that. For instance, how do we determine whether the 35,000-year-old charcoal
found at a site in Chile is from a cooking fire or from a brush fire?"
"Anthropology has been plagued by polarization for a
long time, and paleontology in particular has a long history of animosity between
various camps," Conroy observed. "Being at SAR has been a wonderful
opportunity for me to read the literature, synthesize it, make some sense of
it, and try to present a nonpolarizing voice in these debates."
Affiliation at time of award: Professor
of anthropology and anatomy at Washington University Medical School.
Return to Resident
Scholars 1996-97
