Subscribe
Subscribe
MY AMERICAN SCIENTIST
LOG IN! REGISTER!
SEARCH
 
Logo IMG
HOME > PAST ISSUE > March-April 2011 > Article Detail

FEATURE ARTICLE

Refuting a Myth About Human Origins

Homo sapiens emerged once, not as modern-looking people first and as modern-behaving people later

John J. Shea

The Missing Revolution

2011-03SheaF3.jpgClick to Enlarge ImageIn fact, fossil evidence threatening the Upper Paleolithic revolution hypothesis emerged many decades ago. At about the same time the Paleolithic framework was developed during the 1920s and 1930s, European-trained archaeologists began searching for human fossils and artifacts in the Near East, Africa and Asia. Expatriate and colonial archaeologists such as Dorothy Garrod and Louis Leakey expected that the European archaeological record worked as a global model for human evolution and used the European Paleolithic framework to organize their observations abroad. Very quickly, however, they discovered a mismatch between their expectations and reality when Homo sapiens remains outside Europe were found with Lower or Middle Paleolithic artifacts. Archaeologists started assuming then that the remains dated to periods just before the Upper Paleolithic revolution. But in fact, those discoveries, as well as more recent finds, challenge the notion that the revolution ever occurred.

In Europe, the oldest Homo sapiens fossils date to only 35,000 years ago. But studies of genetic variation among living humans suggest that our species emerged in Africa as long as 200,000 years ago. Scientists have recovered Homo sapiens fossils in contexts dating to 165,000 to 195,000 years ago in Ethiopia’s Lower Omo Valley and Middle Awash Valley. Evidence is clear that early humans dispersed out of Africa to southern Asia before 40,000 years ago. Similar modern-looking human fossils found in the Skhul and Qafzeh caves in Israel date to 80,000 to 120,000 years ago. Homo sapiens fossils dating to 100,000 years ago have been recovered from Zhiren Cave in China. In Australia, evidence for a human presence dates to at least 42,000 years ago. Nothing like a human revolution precedes Homo sapiens’ first appearances in any of these regions. And all these Homo sapiens fossils were found with either Lower or Middle Paleolithic stone tool industries.

There are differences between the skeletons of these early Homo sapiens and Upper Paleolithic Europeans. The best-documented differences involve variation in skull shape. Yet, as Daniel Lieberman of Harvard University writes in the recently published The Evolution of the Human Head, we are just beginning to understand the genetic and behavioral basis for variation in human skulls. [Editor’s note: Lieberman’s book is reviewed on page 158.] It makes no sense whatsoever to draw major evolutionary distinctions among humans based on skull shape unless we understand the underlying sources of cranial variation. There is no simple morphological dividing line among these fossil skulls. Most fossils combine “primitive” (ancestral) characteristics as well as “derived” (recently evolved) ones. Even if physical anthropologists divided prehistoric humans into archaic and modern groups, it would be foolish for archaeologists to invoke this difference as an explanation for anything unless we knew how specific skeletal differences related to specific aspects of behavior preserved in the archaeological record.

Early Homo sapiens fossils in Africa and Asia are associated with “precocious,” or unexpectedly early, evidence for modern behaviors such as those seen in the European Upper Paleolithic. They include intensive fish and shellfish exploitation, the production of complex projectile weapons, the use of symbols in the form of mineral pigments and perforated shells, and even rare burials with grave goods in them. But as Erella Hovers and Anna Belfer-Cohen of The Hebrew University of Jerusalem argued in a chapter of Transitions Before the Transition, “Now You See It, Now You Don’t—Modern Human Behavior in the Middle Paleolithic,” much of this evidence is recursive. It is not a consistent feature of the archaeological record. Evidence for one or more of these modern behaviors appears at a few sites or for a few thousand years in one region or another, and then it vanishes. If behavioral modernity were both a derived condition and a landmark development in the course of human history, one would hardly expect it to disappear for prolonged periods in our species’ evolutionary history.

For me, the most surprising aspect about the debate regarding when Homo sapiens became human is that archaeologists have not tested the core hypothesis that there were significant behavioral differences between the earliest and more recent members of our species. Because modernity is a typological category, it is not easy to test this hypothesis. One is either behaviorally modern or not. And, not all groups classified as behaviorally modern have left clear and unambiguous evidence for that modernity at all times and in all contexts. For example, expedient and opportunistic flintknapping of river pebbles and cobbles by living humans often creates stone tools indistinguishable from the pebble tools knapped by Homo habilis or Homo erectus. This similarity reflects the nature of the tool-making strategies, techniques and raw materials, not the evolutionary equivalence of the toolmakers. Thus, the archaeological record abounds in possibilities of false-negative findings about prehistoric human behavioral modernity.

This issue caught my interest in 2002 while I was excavating 195,000-year-old archaeological sites associated with early Homo sapiens fossils in the Lower Omo River Valley Kibish Formation in Ethiopia. I am an archaeologist, but I am also a flintknapper. Nothing about the stone tools from Omo Kibish struck me as archaic or primitive. (When I teach flintknapping at my university, I have ample opportunity to see what happens when people with rudimentary skills try to knap stone and how those skills vary with experience and motivation.) The Omo Kibish tools showed that their makers had great versatility in effectively knapping a wide range of rock types. This set me to thinking: Have we been asking the wrong questions about early humans’ behavior?








comments powered by Disqus
 

EMAIL TO A FRIEND :

Subscribe to American Scientist