UCI biologist proposes trimming some branches

June 18, 2003

Irvine, Calif., June 18, 2003 -- In a new analysis of recent fossil findings, UC Irvine biologist Francisco J. Ayala concludes that our evolutionary tree is weighed down by too many branches.

Currently, there are as many as seven recognized groups or branches to the Hominid tree, which encompass the entire human lineage. Ayala, who received the 2002 National Medal of Science for advances in evolutionary genetics, believes that paring down the Hominid family tree to four well-defined branches, plus one tentative branch, and redefining the species groups will better illustrate the course of human evolution.

The report appears in the early edition online site of the Proceedings of the National Academy of Sciences (http://www.pnas.org).

"An unnecessary multiplication of categories for classifying our Hominid ancestors distorts our evolutionary biology," Ayala said. "Our proposal provides a clearer overview of human evolution, so that the trees do not obscure the forest or -- a better analogy in this case -- so that a multiplicity of branches does not obscure the growth of the tree trunk."

For most of the 20th century, scientists have traced our human lineage through three Hominid branches -- Australopithecus, Paranthropus and Homo. During the past eight years, however, fossil findings have led researchers to propose adding four new branches to the Hominid tree -- Ardipithecus, Orrorin, Kenyanthropus and Sahelanthropus.

Under closer examination, however, Ayala and co-author Camilo J. Cela-Conde of the Universitat de les Illes Baleares question whether sufficient data has been unearthed to warrant these new branches. They also have doubts whether species in one of these new branches, Sahelanthropus, could walk upright -- an important factor in deciding whether they fit in the Hominid family.

Ayala and Cela-Conde propose trimming the currently recognized human evolutionary tree by eliminating as branches Paranthropus, Orrorin and Kenyanthropus. Instead, Ayala and Cela-Conde would keep three existing branches -- Australopithecus, Homo and Ardipithecus -- then add one new branch called Praeanthropus.

"Specimens that existed in the trimmed branches can be incorporated into this simpler family tree," explained Ayala. "For example, Praeanthropus would encompass the very earliest hominids at the time they split from what would evolve into the chimpanzee family."


-- Praeanthropus. This branch, or genus, would encompass the earliest Hominids - estimated to have split from the chimpanzee family about 7 million years ago. Species in this branch have a developing ability to walk upright. Currently, Praeanthropus is considered a subgenus that connects the Australopithecus and Orrorin branches. In the new tree, Orrorin loses its status as a branch and becomes a subgenus of Praeanthropus.

-- Ardipithecus. This new branch would split off from Praeanthropus about 4.5 million years ago. Its species are notable for distinct differences from the Hominids that evolved into human beings, such as having thin molar enamel, similar to that of the African Great Apes.

-- Australopithecus. Already on the evolutionary tree, this branch would now split off from Praeanthropus about 3.5 million years ago. Species in this branch have a developing jaw and teeth sturdy enough to eat hard vegetables. In the new tree, Paranthropus loses its status as a branch and becomes a subgenus of Australopithecus.

-- Homo. Already on the evolutionary tree, this branch would now split off from Praeanthropus around 3.5 million years ago. Homo species are characterized by larger brains and increased bipedal activity. Homo sapiens, or modern human beings, are part of the Homo branch. In the new tree, Kenyanthropus loses its status as a branch and becomes a subgenus of Homo.

Finally, Ayala and Cela-Conde propose making Sahelanthropus a tentative branch separate from the Hominid tree until more evidence can be found proving this species had bipedal traits.
A complete archive of press releases is available on the World Wide Web at http://www.today.uci.edu.

NOTE TO EDITORS: Image available at http://today.uci.edu/news/release_detail.asp?key=1005.

University of California - Irvine

Related Australopithecus Articles from Brightsurf:

New study records dual hand use in early human relative
Research by anthropologists at the University of Kent has identified hand use behavior in fossil human relatives that is consistent with modern humans.

In South Africa, three hominins, including earliest Homo erectus, lived during same period
Nearly 2 million years ago, three hominin genera -- Australopithecus, Paranthropus and the earliest Homo erectus lineage -- lived as contemporaries in the karst landscape of what is now South Africa, according to a new geochronological evaluation of the hominin fossil-rich Drimolen Paleocave complex.

When three species of human ancestor walked the Earth
In a paper published this week in Science, an international team of scientists share details of the most ancient fossil of Homo erectus known and discuss how these new findings are forcing us to rewrite a part of our species' evolutionary history.

Lucy had an ape-like brain
A new study led by paleoanthropologists Philipp Gunz and Simon Neubauer from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, reveals that Lucy's species Australopithecus afarensis had an ape-like brain.

Ancient hominins had small brains like apes, but longer childhoods like humans
Using precise imaging technology to scan fossil skulls, researchers found that as early as 3 million years ago, children had a long dependence on caregivers.

Skull scans reveal evolutionary secrets of fossil brains
Three-million-year old brain imprints in fossil skulls of the species Australopithecus afarensis (famous for 'Lucy' and 'Selam' from Ethiopia) shed new light on the evolution of brain growth and organization.

'Little Foot' skull reveals how this more than 3 million year old human ancestor lived
High-resolution micro-CT scanning of the skull of the fossil specimen known as 'Little Foot' has revealed some aspects of how this Australopithecus species used to live more than 3 million years ago.

First human ancestors breastfed for longer than contemporary relatives
By analyzing the fossilized teeth of some of our most ancient ancestors, a team of scientists led by the universities of Bristol (UK) and Lyon (France) have discovered that the first humans significantly breastfed their infants for longer periods than their contemporary relatives.

A 3.8-million-year-old fossil from Ethiopia reveals the face of Lucy's ancestor
Cleveland Museum of Natural History Curator of Physical Anthropology Dr.

Maternal secrets of our earliest ancestors unlocked
New research brings to light for the first time the evolution of maternal roles and parenting responsibilities in one of our oldest evolutionary ancestors.

Read More: Australopithecus News and Australopithecus Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.