Early Human Fossils Change Concepts Of Human Evolution

Two University of Utah geologists helped date volcanic ash deposits used to determine the ages of two early human fossils that were discovered in Kenya and challenge popular notions of how humanity evolved.

The study, published in the Thursday, Aug. 9 issue of the journal Nature, was conducted by nine researchers, including famed paleontologist Meave Leakey, her daughter Louise Leakey and University of Utah geologists Frank Brown and Patrick Gathogo.

The first fossil is a 1.44 million-year-old jawbone of Homo habilis, the earliest species of our genus, Homo. It shows that for a half-million years, two species of early humans lived side by side in Africa, contrary to the old view that one species, Homo erectus, evolved from the other, Homo habilis.

If the fossils have been correctly identified as to which species they belong, “then the most important conclusion is that there was more than one species of early man for an extended period of time in East Africa,” said Brown, a professor of geology and geophysics and dean of the University of Utah College of Mines and Earth Sciences.

"As you go through time, in general there was more than one hominid. Yet today Homo is represented by only a single species: us,” Brown said last week from Nairobi, Kenya.

The other fossil is a 1.55 million-year-old skull of Homo erectus, which is much smaller than a previously discovered specimen, indicating the species was much less like modern humans, Homo sapiens, than previously believed. The variation in Homo erectus skull sizes also suggests males in this species of early human may have had multiple mates.

Brown and Gathogo contributed to the study by determining the order of volcanic ash layers above and below the fossils, allowing scientists to determine the ages of the fossils. Dating the mineral feldspar in the ash layers provided numerical age estimates for the fossils.

“Frank and I have worked in detail the geology of the area on which the paper focuses,” says Gathogo, a University of Utah doctoral student in geology and geophysics. “We understand well enough how the layers of sedimentary rock that preserved these fossils relate with ancient environments, and we have worked together with Ian McDougall of Australian National University in estimating the ages of these rocks.”

As Nature prepared to publish the study this week, Brown was trying to fly home to Utah from Nairobi after his latest field season at Ileret, east of Lake Turkana in Kenya. He is expected no later than Aug. 15.

Gathogo is currently in Salt Lake City and is available for interviews regarding the sediment dating process.

The news release below was prepared by Fred Spoor, first author of the new study and a professor of evolutionary anatomy at University College London.