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Johns Hopkins UniversityArts and Sciences Magazine


Hot New Insights into
Life of Human Ancestors

Recently published studies by teams including faculty members in the Morton K. Blaustein Department of Earth and Planetary Sciences reveal new details of life on Earth millions of years ago. Such details offer insights into the diversity of the diet of early hominids in what is now northern Kenya and the consistently hot climate that likely aided evolution, as well as new evidence supporting the notion that pre-humans in East Africa inhabited savannas, not forests, as previously believed.

Naomi Levin, an assistant professor in Earth and Planetary Sciences, served as the main geologist on an international team of scientists that has spent several years excavating and studying a remarkably preserved 1.95 million-year-old site in northern Kenya. The team found that early hominids living there ate a wider variety of foods than previously thought, including fish, turtles, and crocodiles. Rich in protein and nutrients, these foods may have played a key role in the development of a larger, more human-like brain, which some anthropologists believe happened around 2 million years ago.

Using a variety of techniques, the team was able to conclude that the hominids butchered at least 10 individual animals using simple, sharp-edged stone tools.

A paper on the team's findings was published recently in the Proceedings of the National Academy of Sciences and offers the first-ever evidence of such dietary variety among early pre-humans.

In a separate study published in the same journal, Benjamin Passey, also an assistant professor in Earth and Planetary Sciences, concluded that the Turkana Basin of Kenya—one of the key places where fossils have been found documenting human evolution—has been a very hot place for the past 4 million years. Determining the ancient climate in that region has been difficult until recently; Passey was part of a team at the California Institute of Technology that developed a geochemical approach to determining ancient temperatures.

The method allowed Passey to conclude that the average daily temperatures in the Turkana Basin were in the mid-90s F or higher, year-round.

Passey's research supports the "thermal hypothesis" of human evolution, which holds that pre-human ancestors began walking upright because it was cooler than crawling on all fours. The loss of body hair (fur) and the ability to regulate body temperature through perspiration would have been other adaptations helpful for living in a warm climate, according to this theory.

Another line of research pursued by Levin has found that pre-humans in East Africa 4.4 million years ago lived amid grassy plains dotted with trees and shrubs, a conclusion at odds with a prominent existing theory.

In a commentary published in Science, Levin's team—eight geologists and anthropologists from seven universities led by Thure E. Cerline of the University of Utah —examined the data from a theory put forth in 2009 by University of California at Berkeley researcher Tim D. White and drew a very different conclusion. Studying the environment inhabited by Ardi, an omnivorous, ape-like creature that lived in what is now Ethiopia, the team found that tropical grasses com­prised 40 percent to 60 percent of the biomass.

White had theorized that the early beings lived in a mostly forested environment. His research has been used as an argument against a long-standing theory of evolution known as the "savanna hypothesis," which posited that the major divergence between pre-humans and other great apes was driven by the pre-humans moving out of the forests and onto the grasslands.


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Department of Earth
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