Making sense of new discoveries in the human family tree

New fossil remains discovered in South Africa may be a transitional species between “Lucy,” the 3.2 million-year-old fossils discovered by ASU professor Donald Johanson, and our own evolutionary branch of the human family tree. Top national news outlets, including CBS News "60 Minutes," contacted ASU paleoanthropologist Bill Kimbel and Johanson prior to the announcement of the new discovery in the journal Science  for expert analysis and evolutionary context. As founding director and current director of the ASU Institute of Human Origins, Johanson and Kimbel, respectively, are top, sought-after experts in the world in this field and among the first to be consulted on any new discovery.

In an interview that aired on CBS News’ "60 Minutes," Johanson explained the new findings as “a positive defining moment” though his opinion differs with the discovery scientist and American paleoanthropologist Lee Berger's determination that the fossils belong to the australopithecines group like the Lucy skeleton, which has come to symbolize human evolution. Berger is with the Institute for Human Evolution at the University of the Witwatersrand in Johannesburg, South Africa. The new fossils, named Australopithecus sediba, were found in an area known as Malapa near Johanesberg in the Cradle of Humankind, a World Heritage Site. In a Wall Street Journal interview, Johanson said, “I would not be surprised if the Malapa material represents a newly recognized species of Homo.”

The mix of primitive and advanced traits shown in the skeletal remains is sparking debate over where on the family tree the new species belongs and raising important questions about the dawning of Homo.

Johanson, having already viewed the fossils at the University of Witwatersrand in South Africa, provided a detailed analysis via email to MSNBC.com. In it, Johanson said, “We have a very comprehensive understanding of the dating, diversity and relationships between the species of Australopithecus, but we know relatively little about the origins of our own genus. Thus, anything found that represents early Homo is potentially of some importance. I think these finds will refocus attention on the South African fossil sites and strengthen the importance of these sites for a more complete understanding of the human family tree."

The ASU Institute of Human Origins is currently working in South Africa in Mossel Bay, a coastal area east of Cape Town, through National Science Foundation and Hyde Family Foundation funded research led by ASU professor Curtis Marean. The sites are mostly large caves in the steep coastal cliffs above the Indian Ocean. These excavations are targeted at refining our understanding of the origins of modern human behavior and placing that event in its environmental context.

Kimbel says that the new fossils reveal the pace of change in early human ancestors. Time.com quotes Kimbel’s view that “what it tells us about the early stage of the Homo lineage is, for example, that there were already substantial changes in the face, the teeth and the pelvis, while the brain size and limb proportions were still reasonably limited," he says. "Having that calendar of change allows us to pose questions about what forces were driving that calendar."

“It is often a toss-up whether a fossil discovery will bring order or confusion to the family tree,” said Kimbel in a New York Times front-page story. “The small brain and long upper limbs [are] indicative of Australopithecus, but those are signs of its ancestry, not its future,” he said for a Wired Science interview. “The significance is in the patterns and insights it provides. These specimens fall at the young end of a very puzzling million-year period in hominin evolution. Whether or not A. sediba is our ancestor, it could help us understand the dynamics that led to the split producing the lineage culminating ultimately in us,” said Kimbel.

The Institute of Human Origins is supported by Arizona State University research and academic units including the Institute for Social Science Research and School of Human Evolution and Social Change in the College of Liberal Arts and Sciences. For more information and research on the human evolutionary timeline, see http://becominghuman.org.

To see Johanson talk about human origins, go to the multimedia news section at iho.asu.edu/news.

Links for other news outlets can be found here:

MSNBC.com (Johanson) Link here
New York Times (Kimbel) Link here
Wall Street Journal (Kimbel) Link here
Inside Science News Service (Kimbel) Link here
Los Angeles Times (Kimbel) Link here
National Geographic News (Kimbel) Link here
Scientific American (Kimbel) Web article link here; magazine coverage article link here
Time Magazine (Kimbel) Link here
Wired magazine (Kimbel) Link here