We’ve had just enough cool weather in recent weeks to tease my appetite into autumn mode. When the thermometer registers in the 50s at night, I can feel myself beginning to crave the slightly denser foods we generally eat in fall and winter.

It’s just as well that I’m not hankering for a garden salad because anything resembling home-grown produce will be a memory until next spring. In fact, where I most often eat lunch, the salad bar is stocked with mixed lettuce that the cafeteria workers shake out of a bag, already torn into bite-sized pieces. As if to underscore the point that summer has passed, even the iceberg lettuce looks more chlorophyll-deprived and anemic than usual.

I’ve never been sure whether our food preferences change for biological reasons or pragmatic ones. It’s certainly convenient that we stop thinking of lighter fresh foods when they’re no longer in season and spurn heavier, baked dishes when it’s too hot to turn on the oven. However, during a significant portion of our evolution, human beings in cold climates, like other animals, have had to put on fat for the winter, and this makes me think that this has a lot to do with natural processes.

The fact that we can now set the thermostat in our homes at 72 degrees year-round doesn’t change this cycle of appetite. Perhaps people who live in climates temperate enough to support a 12-month growing season can shake loose of it, but when the days get shorter, I want to feel fuller. I want what I eat to stick to my ribs.

One of the foods I begin to think about during the fall is the sweet potato. This is where my logic about seasonal foods runs aground. In this climate, the sweet potato is an autumn food by design, not biological destiny.

When most of us think sweet potato, we conjure up an image of a casserole or pie served alongside turkey. I suspect this has something to do with its pumpkinesque coloring and the fact that marketers have convinced us that the sweet potato is a fall food. In any case, it’s not what nature intended for Kansans to eat this time of year.

As it happens, the sweet potato, which is not really a potato at all, is native to the tropics. It’s actually part of the root system of the morning glory, which explains why people who know what they’re doing often plant sweet potatoes for their flowers.

In the U.S. diet, sweet potatoes have traditionally been a Southern food. Most sources define them as a native food of the Americas Columbus reported his first sweet potato sighting in the Caribbean but culinary genealogists say they were taken to the Caribbean from South America. After they arrived in the New World, European immigrants began to cultivate them.

Sweet potatoes can be stored for several months, which means that they can be transported easily from region to region, but it’s not likely that sweet potatoes turned up on a menu anywhere outside the South for quite some time after European settlement. They would have been late-comers to Midwestern diets because they don’t grow easily here.

Sweet potatoes are highly sensitive to frost and our growing season some years is barely long enough for them. The tubers can take as long as 170 days to mature, when grown from plants, and the plants themselves are very sensitive to frost. I think I’ve tried twice to grow them and all I got was morning glories. The roots hadn’t turned into tubers worth mentioning by the time the frost killed off the vines.

Our grocers begin pushing sweet potatoes in the fall because they’re selling the summer crop that has been harvested in warmer climates and shipped north. That’s the only thing that makes sweet potatoes a fall food in Kansas.

I know all this, and when the temperature dips, I’m still convinced it’s time to eat sweet potatoes.