Stereotypes are almost always the conclusions of lazy science—they're just empirical generalizations that are stripped of their variances and encoded as fact into the collective consciousness of a general population. They're the tools of propagandists, xenophobes, and oppressors, and tend to stick around through the ages like a bad smell.

However, sometime a stereotype will reveal a hidden truth that provides an origin to the myth.

The trope of the "lazy Southerner" dates back to America's postbellum period following the end of the Civil War. No one really knew where it came from, but the image of a lethargic, filthy, drawling farmer has pervaded art, literature, and popular culture up until this very moment.

One argument, recently published by Rachel Nuwer for PBS Nova Next, presents some compelling evidence for the theory that a hookworm epidemic was responsible for this rural stereotype.

The hookworm (Necator americanus) is a parasite that's been called "the germ of laziness," due to the exhaustion and mental fogginess it tends to inflict upon its victims. Historical evidence shows the parasite ravaged the American South throughout the early 20th century, as a result of poor sanitation and a lack of public health programs among the poor.

Necator americanus. Image: Flickr/Internet Book Images

By 1905, the parasitologist Charles Stiles estimated that 40 percent or more of the Southern population was infected with hookworms. The parasite thrives in fecal matter, and the combination of shoddy waste disposal and the rarity of shoes allowed hookworm larvae to enter people's bodies through the webbing between their toes.

Once hookworms have penetrated the skin, they'll travel through their host's lungs and into their intestines, where they'll survive on a diet of blood they suck out from the intestinal wall. A female hookworm can lay up to 10,000 eggs in a single day, which gives you an idea of how rampant a localized infestation can become in a very short time.

The "laziness" that's synonymous with hookworm infections is a symptom of iron deficiency anemia, due to blood loss.

In poor, malnourished victims, the parasite can cause stunted growth and weakness. Children with hookworms were plagued with attention deficit disorders and lower IQ, and the infected often had strange food cravings for dirt, clay, paper, and chalk.

Unfortunately, Southern states were the nexus for a hookworm-friendly climate, as the parasite loved the sandy soil that makes the region so fertile.

In 1910, 7.5 million Southerners had hookworms, according to an investigation conducted by the Rockefeller Sanitation Commission for the Eradication of Hookworm Disease. It would take 50 years for the worm to be eradicated from the South. Better sanitation infrastructure, farming mechanization, Franklin Roosevelt's New Deal, and the end of sharecropping almost entirely freed the region from hookworms by 1985.

We're still not absolutely positive that hookworms brought about the "lazy Southerner" stereotype—there's just not enough definitive evidence to support that. But what we do know, according to 20th century census data and health records, is that areas without hookworm infestations reported greater economic and educational gains.

So much of history can be told through the rise and fall of disease epidemics, and the legacy of the American South has been shaped a great deal by the tiny hookworm. The physical stereotypes borne out of its takeover may have disappeared with advances in medicine and healthcare, but some elements of the "lazy Southerner" myth have persisted.