It's probably a little of hardwire and a little of learning, and a lot of just impulse, but I would argue that the impulse is not to put on pounds per se, but to get warm. German food sounds better to me when I'm cold and it's cold outside, and chilled gazpacho soup sounds better to me when I'm hot and it's summertime. Is it because of some long-term outlook in the body to put on pounds for future fuel needs? Or just because we're more likely to want to fuel up (for right now, to heck with putting on pounds against our future hour of need) when we are physically cold?
Sounds false as stated, but here's how it might have worked historically: at the end of the fall harvest you might eat more to store up some energy, but in any locale with a truly cold winter there wouldn't actually be much to eat so people would naturally get thinner until spring, as humans don't hibernate to save energy output. As civilization changed, people changed as well, learning how to dry and ferment and therefore store food, but it still would have been much scarcer than in warmer months so again, probably less eating due to less food to eat. Harder to hunt and gather, so more energy expended. As civilization changed further, with humans migrating to colder and colder climates, no longer stuck in the tropics, sure, they changed. Skin got white so they could better absorb vitamin D. Less sun, fewer plants to eat, more reliance on animal food, but fewer animals around. More fat consumed in these colder climes but again, much more energy exerted to find the food. Civilization advances further to agriculture, with drying of fruits and grains and more year-round food, but not in the far northern areas where it was too cold. Those people ate more animal, in hotter climes more plants and more abundance year-round except in drought. To cut this short of the entire extent of human evolution, as we changed and moved all over the place, different cultures developed according to the climate. There wouldn't have been the same effect on all humans everywhere. And now, we have indoor temperature control, and have for a long long time, so we would have changed and are still changing. Evolution doesn't stagnate. Changes may be too small to notice, but they're happening. I wouldn't put much stock in any theory of human nature, as it keeps changing with the cultural and climate and technological changes. When a creature develops a cerebrum, it's pretty hard to tell if anything is really hard-wired or not, and since we don't hibernate, we don't really need to store that much energy.
Being the researcher I am, I actually did a search to see what I could find.
Traditionally, food was more scarce in winter, so the impulse was to eat and store fat when possible. Because of this, most of us tend not to pass on the sweet, unhealthy foods for which this time of year is notorious.
Add to the fact that for many of us, it's cold outside and we're less likely to be out doing our normal/usual activities - sports, walking, gardening and other things that keep us moving and help keep off the extra pounds.
I'm totally with AnnieBrooke - when it's cold out, I'm going to lean toward comfort foods, such as mashed potatoes, mac and cheese, etc. On the other hand, when it's warm/hot, I'll lean toward a nice cool salad, etc.
I am learning to replace those comfort foods with healthier versions, so that's always something to look at, as well.
I would guess at this point Barb, I'm very susceptible to predators. LOL (crack myself up). I absolutely have some kind of internal something that makes me do the same as you . . . I want hot, creamy, savory, rich and filling comfort food as the temps drop. Throw me a piece of toast on plate, add roast beef and smother with mash potatoes and gravy on it! Now, I'd never eat that in the summer when I long for salads and fruit plates like you do. :>)) We must be animalistic in our urges. (stll cracking myself up).