Shift in our ancestors' diet longer in the tooth than we believed

A team of scientists has reported an earlier date of shift in the diet of human ancestors.

Millions of years ago, our primate ancestors turned from trees and shrubs to search for food on the ground. In human evolution, that has made all the difference.

The shift towards a grass-based diet marked a significant step toward the diverse eating habits that became a key human characteristic, and would have made these early humans more mobile and adaptable to their environment.

The Johns Hopkins University scientist shows that this significant shift took place about 400,000 years earlier than experts previously thought, providing a clearer picture of a time of rapid change in conditions that shaped human evolution.

Lead author Naomi E. Levin said the diet shift is one of an array of changes that took place during the Pliocene era - 2.6 million to 5.3 million years ago - when the fossil record indicates human ancestor species were starting to spend more time on the ground walking on two feet. Understanding the timing of these events can help show how one change related to another.

The paper reports on an analysis of fossil teeth found in Ethiopia that shows the shift from a diet based on trees and shrubs to one that included grass-based foods took place about 3.8 million years ago - roughly 400,000 years earlier than the date supported by previous research. (Grass-based foods could include not only grasses and their roots, but also insects or animals that ate grass.)

The shift in eating habits would have broadened our ancestors' horizons and improved their species' capacity for survival, Levin said.

The study appears in Proceedings of the National Academy of Sciences.