Why do you keep losing weight and then putting it back on?

If you think about it, until about 1980 it was good for human beings (and all animals) to have this characteristic. In ancient times or in prehistoric times, food was hard to come by--so gaining weight easily was something that natural selection preferred since people who gain weight easily lived longer and reproduced more frequently.

Since ca. 1980, humans are now plagued with the problem of being overweight because food is so easy to acquire (not helped by insane agricultural and food policies in countries such as the United States).