New research revealed early humans started using fire between two and three million years ago when Africa's environment became increasingly fire-prone.
Fire is an ancient tool, historically used for cooking, constructing, hunting and even communicating. However, when exactly our ancestors started using it has remained a topic of hot debate.
Now, anthropologists from the University of Utah suggest humans used fire to their advantage, as Africa's environment grew drier and natural fires occurred more frequently. The use of fire not only allowed humans to more efficiently search for and handle food, but also allowed them to travel farther distances and expand into other continents.
Current theories surrounding how fire came about suggest it happened by mere accident: pounding rocks against each other to create a spark that later spread to a nearby bush.
"The problem we're trying to confront is that other hypotheses are unsatisfying. Fire use is so crucial to our biology, it seems unlikely that it wasn't taken advantage of by our ancestors," explained Kristen Hawkes, senior author of the study.
The University of Utah's proposed scenario is the first known hypothesis in which fire does not originate serendipitously.
Instead, researchers show that increased aridity and flammable landscapes led to the exploitation of fire's food foraging benefits. In this case, early humans would have simply adapted to such environmental changes.
"All humans are fire-dependent. The data show that other animals and even some of our primate cousins use it as an opportunity to eat better; they are essentially taking advantage of landscape fires to forage more efficiently," Hawkes added.
Researchers came to this conclusion by reconstructing the climate and vegetation of tropical Africa between two and three million years ago.
Woody plants and fire-prone tropical grasses have distinct carbon isotopes that are evident in paleosols, or ancient dirt. Therefore, the presence and composition of specific paleosols indicates what kind of vegetation was growing millions of years ago.
Carbon analyses of paleosols from the Awash Valley in Ethiopia and Omo-Turkana basin in northern Kenya and southern Ethiopia revealed a consistent pattern of tropical, fire-prone grasses replacing woody plants 3.6 to 1.4 million years ago.
Burning off forest cover would have exposed otherwise obscured holes and animal tracks, therefore reducing the time needed for hunting. Fire would have also cleared the land and made it easier to grow food.
Furthermore, foods altered by burning take less effort to chew. This helps explain anatomical evolutionary changes such as reduced tooth size and jaw structures related to chewing. Requiring less effort also means early humans would have had an increased energy budget and could have traveled longer distances.
"This scenario tells a story about our ancestors' foraging strategies and how those strategies allowed our ancestors to colonize new habitats," Hawkes said. "It gives us more insight into why we came to be the way we are; fire changed our ancestors' social organization and life history."
Their study was recently published in the journal Evolutionary Anthropology.
