Women of African descent do store higher levels of subcutaneous fat than average - the benign kind of fat that doesn't increase health risks. Food scarcity isn't at all unique to Africa though, especially on an evolutionary time scale, and places like the Balkans have had food scarcity problems in living memory, as did Europe as a whole in the 19th century and before. Plus, from a thermodynamics perspective, there's only so much energy you can extract from a given amount of fat.