Fossil Study Answers Questions Regarding Dietary Changes in Human Ancestors

As a result of selection and adaptation over the course of millions of years, diverse life-forms consistently drive alterations. Through examining fossils, changes over time can be identified — even behavioral changes such as dietary shifts.

Chalachew Seyoum, PhD, assistant professor in the University of Arizona College of Medicine – Phoenix’s Department of Basic Medical Sciences, explored that phenomenon in a new study published in Science.

To solve how dietary changes shifted the morphology of primates, Dr. Seyoum and his team focused on a specific behavior in the fossil record of some primates. By reporting carbon and oxygen isotope ratios from fossil cercopithecid monkeys, they found that changes in graminivorous behavior preceded changes in dental morphology by 700,000 years.

“With every organism, there is a change in morphology and a change in our adaptation, a change in our diet and other things,” Dr. Seyoum said. “This study is showing that sometimes behavioral and morphological changes can happen successively, instead of concurrently.”

Dr. Seyoum states that there has been a dietary shift in the human lineage from a C3 dominated diet, which mostly consisted of plants that utilize the C3 carbon fixation pathway, to more grass and sedge based C4 diet. According to Dr. Seyoum, dietary change is linked to climate and habitat change.

Two obstacles remain in detecting behavioral drive-in fossil records. It is challenging to quantify behavior independently of the morphological trait, and behavioral drive sequences can vary in duration, thereby eliminating a chronological offset.

However, Dr. Seyoum and his team overcame these obstacles by focusing on the consumption of C4 plants in primates, with the absence of adequate adaptations that are in most graminivorous mammals.

By examining the oxygen isotopes of fossils and placing the data within the context of dietary evolution, Dr. Seyoum and colleagues found that graminivorous behavior came about 700,000 years before the changes in dental morphology.

Technological advancements have allowed studies such as the one conducted by Dr. Seyoum to explore questions about the past. Although much remains uncertain, future data and technology may facilitate more innovative research.

“Many years ago, we did not have the privilege to sample isotope data, and we were not in a position to achieve this kind of outcome,” Dr. Seyoum said. “Now this type of data analysis is becoming increasingly common. However, additional fossil data is needed to better understand our past and fill in the gaps.”