Rethinking Human Evolution

Introducing Ardi

“Throw out all those posters and books that depict a living ape evolving into a human being,“ Lovejoy said. Lovejoy is one of the primary authors who revealed the research findings on Ardipithecus ramidus, a hominid species that lived 4.4 million years ago in what is now Ethiopia.

“People often think we evolved from ancestors that look like apes, but no, apes in some ways evolved from ancestors that look like us,” he says. “It has been a popular idea to think humans are modified chimpanzees. From studying Ardipithecus ramidus, or Ardi, we learn that we cannot understand or model human evolution from chimps and gorillas.”

A special issue of Science (www.sciencemag.org) featured 11 papers that are the first formal description of Ardi, a partial female skeleton. Lovejoy was first author on five papers and contributed to an additional three in the Oct. 2, 2009, issue of the journal. For seven years, he has been a part of a major international research effort studying Ardi, serving as post-cranial anatomist and behavioral theorist.

“Ardi is one million years older than Lucy, more informative than Lucy, and Ardi changes what we know about human evolution,” Lovejoy says.

Ardi received the top honor as the Breakthrough of the Year, named by Science and its publisher, AAAS, the world’s largest science society. Time magazine also named Ardi its Scientific Breakthrough of the Year.

Meet Lucy’s Great-Grandfather

Lovejoy worked with Dr. Yohannes Haile-Selassie of the Cleveland Museum of Natural History and other colleagues to announce the discovery of an important new early hominid partial skeleton from Ethiopia. A press statement released by the Authority for Research and Conservation of Cultural Heritage (ARCCH) and the Woranso-Mille project stated that one of the specimen’s most important revelations is that advanced human-like, upright walking is very ancient, as the new specimen is 400,000 years older than the famous Lucy skeleton. Lovejoy and Haile-Selassie served as corresponding authors of the analysis of the new specimen published in the Proceedings of the National Academy of Sciences (PNAS) early online edition. PNAS is one of the world's most-highly cited multidisciplinary scientific serials.

The 3.6 million-year-old partial skeleton belonged to Lucy’s species, Australopithecus afarensis. It was found by an international team of scientists led by Haile-Selassie. This team has been conducting field research in the Woranso-Mille area of Ethiopia’s Afar region since 2004. Haile-Selassie and his field team members excavated the partial skeleton for five years after the discovery of the first element in 2005. The new partial skeleton has been nicknamed Kadanuumuu (kah-dah-nuu-muu), which means “big man” in the Afar language and reflects its large size. The male individual stood between 5 and 5 ½ feet tall, even though Lucy stood only about 3 ½ feet tall.

Kadanuumuu becomes the oldest Austalopithecus afarensis skeleton yet found and is among the largest individuals of its species. It not only preserves most of the same skeletal parts that Lucy does, but also other skeletal structures that  have never been previously known. These shed new light on previously unknown anatomical features of Australopithecus afarensis and advance our knowledge of the paleobiology of this species and its descendants.

“Kadanuumuu is about as complete as Lucy, “Lovejoy says. “They both have pelves, a complete lower limb bone and elements of the forelimb, vertebral column and thorax (chest cage). However, the new specimen has more complete ribs and a nearly complete scapula (shoulder blade), which tells us much more about body form than Lucy was able to.”

The best-known direct early human ancestor is Australopithecus afarensis. The only partial skeleton assigned to this species until now has been Lucy, a female individual that dates to 3.2 million years ago. Lovejoy helped reconstruct Lucy, which was discovered in 1974.

The new specimen’s skeleton reveals that it is a highly evolved biped. “It turns out that some of Lucy’s characters, which were argued to indicate that she was not fully adapted to upright walking, were in fact just due to her unusually small size,” Lovejoy explains. “Kadanuumuu corrects those impressions. It also tells us that the shoulder and thorax of Lucy’s species were very different from those of chimpanzees. These findings further confirm what we concluded from Ardi, that chimpanzees have undergone a great deal of specialized evolution since we shared a last common ancestor with them.”

When compared to Lucy and Ardi, Lovejoy said Kadanuumuu provides vital new and additional information. “It’s Lucy’s great-grandfather in the sense that it is male and much larger,” he says. “It thereby solves a number of issues that Lucy could not because she was so small. Ardi was transformational in terms of our understanding of the origins of humans, including Lucy’s and Kadanuumuu’s species. Of course, Lucy was the first whereas this specimen follows in her footsteps, so to speak, but the new specimen confirms some of the features that we hypothesized were present in Ardi.”

Lovejoy worked closely with Haile-Selassie and Dr. Bruce Latimer of Case Western Reserve University on this discovery. Other authors provided geological data and analysis.

About Lovejoy

A resident of Kent, Ohio, Lovejoy has taught at Kent State for more than 40 years. He is a widely published author, with nearly 150 articles about human evolution, forensics, demography, biomechanics and evolutionary theory. He holds the honor of being one of the Institute for Scientific Information’s (ISI) Most Highly Cited authors in the general social sciences. In 2007, Lovejoy was elected to the National Academy of Sciences (NAS), one of the highest honors given to a scientist in the United States.