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The Quest for Adam Volume 52 Number 4, July/August 1999
by Jean-Jacques Hublin

[image] Placement of the new-found A. garhi is uncertain; its discoverers have suggested it is a descendant of A. afarensis, but what, if any, later species it gave rise to is unknown. Recent dating indicates H. erectus may have survived in Southeast Asia until 50,000 years ago, but this awaits confirmation. (Lynda D'Amico; phylogenetic tree adapted from a schematic by George Washington University's Bernard Wood) [LARGER IMAGE]

From the earliest-known human ancestors to the manner in which our forbears spread our across the globe, our understanding of human evolution has changed dramatically in the past half-century. Among the most notable advances was simply convincing the public, and even some scientists, that humans were part of the animal world. The clearest expression of the resistance to this notion is that chimpanzees, gorillas, and orangutans are still assigned to a separate family, Pongidae, while humans and their ancestors have been placed in their own family, the Hominidae.

As late as the 1970s, the two families were considered to have evolved separately for a very long time, perhaps 20 to 28 million years. In 1966, however, Vince Sarich and Allan Wilson of the University of California, Berkeley, analyzed the molecular evidence for the relationships among the apes and concluded that the divergence between chimpanzees and humans could not have happened much before 5 million years ago. Their results have been confirmed by subsequent molecular studies, especially of DNA. These show that chimpanzees and gorillas are much more closely related to humans than they are to orangutans. Chimpanzees share more than 99 percent of their genetic material with humans, even though it is packaged in their chromosomes in a different way. In 1992, Tim White of the University of California, Berkeley, and his collaborators discovered Ardipithecus ramidus in Ethiopia. This species, which seems to be very close to the point of divergence between chimpanzees and human ancestors, dates to 4.4 million years ago, perhaps confirming the genetic evidence.

With information provided by the many fossil species that have come to light in recent years paleoanthropological research has shifted from Europe and Asia to Africa. This continent appears more and more as the demographic and evolutionary core of human development. We were originally tropical primates who adapted to a dry and open environment. From this vast continent several waves of colonists spread into Eurasia and eventually to Australia and the Americas. More and more, these movements are being related to environmental changes.

Fossil hominids are increasingly considered in a biological perspective, as members of extinct populations. Paleoanthropologists are paying more attention to their individual variation, biological adaptation, pathology, and physiology. Nowadays the understanding of their evolution takes into consideration the ecological changes as well as the interaction between cultural and biological factors.

The relations between some branches of our family tree are still debated, but today we have a much sharper--albeit much more complex--image of hominid evolution than the naive picture of the late 1940s. Our family tree is no longer a linear series of species but a dense bush with many dead branches. The quest for the famous "missing link" has become vain simply because we no longer deal with a simple chain.

Jean-Jacques Hublin, a director of research in France's Centre National de la Recherche Scientifique in Paris, is head of the Dynamics of Human Evolution Laboratory.

* Companion articles: "Rethinking Human Evolution" and "Perspectives on the Past"

© 1999 by the Archaeological Institute of America