About 2.5 million to 1.4 million years ago, when the genus Homo emerged, Africa became drier. During certain seasons, already dry savannas became even more arid, making it difficult for hominids to find adequate food. But Wrangham’s team argues that even in this inhospitable environment there were oases: wetlands and lake shores.
In these aquatic habitats, water lilies, cattails, herbs and other plants would have had edible, nutritious underground parts—roots and tubers—that would have been available year-round. These “fallback” foods would have gotten hominids through the lean times.