There are some interesting ideas about food, evolution and body metabolism posted here. I agree with the observation and common sense deduction that whoever lives through a long cold winter and a food shortage will be the Mommies and Daddies of the next generation. I also agree it may be a factor in why people tend to get fat and love all the 'wrong' things in their diet, sweets, fat,and salt. These items are generally scarce in hard times, yet provide energy and minerals we need. Disease also played a key role in 'selecting' those who lived and died. Obviously if you died of diarrhea from some common intestinal bug when you were two, you won't be raising any kids. ( Don't laugh, diarrhea is still the most common killer of children in third world countries) Anyway that's the basic 'selection of the fittest' scenario. The scenario plays out differently as the situation changes. Being fat and craving carbohydrates, salt, and fat isn't a healthy thing in our time of relative abundance. Maybe we have the wrong genes, but we do have a brain, that can say NO.
What happened to the Clovis People? The art of making their elaborate arrowheads, Clovis Points, which were really stunning works of art and very distinctive, disappeared from the Americas. One theory has the original Clovis people spreading to the ends of the Americas, and then being eliminated by successive waves of migrations across a frozen Bering Straight from Asia. There are no Clovis points found in Asia or Alaska but there are very similar to Solutrean points found in Europe. Needless to say this has generated a LOT of discussion and controversy, as has the discovery of the Kennewick Man, the Spirit Cave Lake man and dozens of other very early mummies over 8000 years old. Some of the mummies had red hair. I mention this so others can research the situation. It will make a fascinating story once they sort out what happened those thousands of years ago.
In the mean time, I wonder how my skinny progenitors made it through the last ice age ;-)