Final answer:
Genes that enable people to store energy in the form of fat in anticipation of leaner times have been passed down from ancestors who lived as hunter-gatherers. These genes are part of the thrifty gene hypothesis, which suggests they helped people survive famines. However, in modern times, excess fat accumulation is becoming a health threat.
Step-by-step explanation:
The genes that enable people to store energy in the form of fat in anticipation of leaner times are believed to have been passed down from ancestors who lived as hunter-gatherers. These genes are part of the thrifty gene hypothesis, which suggests that they evolved because they allowed people to burn fewer calories and store the rest as body fat, helping them survive famines.
Our earliest ancestors lived as hunter-gatherers, and they would settle in an area for a brief time when there were abundant resources. They hunted animals for meat and gathered wild fruits, vegetables, and cereals. They ate what they caught or gathered as soon as possible because they had no way of preserving or transporting it. Once the resources of an area ran low, they would move on.
In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat. Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation.