Did climate change cause infections 6,000 years ago?

New study of human skulls finds infections peaked due to high population density, poor hygiene and climate conditions

Researchers at Tel Aviv University have discovered evidence of ear infections in the skull remains of humans living in the Levant some 15,000 years ago.

“Our research seeks to determine the impact of our environment on illnesses in different periods,” says lead author Dr. Hila May of the Department of Anatomy and Anthropology at TAU’s Sackler Faculty of Medicine and the Dan David Center for Human Evolution and Biohistory Research at the Faculty of Medicine, located at the Steinhardt Museum of Natural History. “Using advanced technologies and unique methods developed in our lab, we have been able to detect signs of prolonged inflammation in the middle ear.”

The researchers found a decline in morbidity as a result of ear infections following the transition from hunting and gathering to farming on account of changes in living conditions. A peak in morbidity, however, was observed in a sedentary population living about 6,000 years ago (Chalcolithic period).  

Dr. May says the reason for this is twofold: social and environmental: “We know from archaeological excavations of this period, similar to preceding periods, people lived in a communal area where all activities, from cooking to raising livestock, took place. As a result, the population density in the ‘home’ was high, hygiene was poor and they suffered from indoor air pollution. Two other factors known about this period – dietary change, the advent of dairy consumption, and climate change, a dip in temperature and a rise in rainfall, also contributed to the prevalence  of ear infections.”

A story in the skulls

Until the advent of antibiotics in the 20th century, ear infections developed into chronic conditions, or, due to complications, caused permanent loss of hearing or even death. “Ear infections are still a very common childhood ailment, with over 50 percent of young children today still suffering from an ear infection at one point or another,” explains Dr. May. “The reason for this is that the tubes that channel fluid from the middle ear to the mouth are underdeveloped in young children, so fluids that accumulate in the ear ultimately cause inflammation.”

 “A prolonged ear infection would cause permanent damage to the bony wall of the middle ear, which is remarkably preserved into adulthood, so when we sought to investigate changes in communal health over time in our region, we chose to focus on ear infections, developing a special method for doing so,” she adds.

The scientists used a videoscope, a tiny camera mounted at the end of a flexible tube, which they inserted through the ear canal to the middle ear to observe its bony walls. In addition, they scanned skull remains with a high-resolution micro-CT, and also examined the middle ear’s bony wall using a light microscope.

More room, fewer infections

As living conditions improved, morbidity as a result of ear infections dropped, according to the study.

“Houses were larger and featured several rooms, including separate areas for specific activities, i.e. the kitchen was set up in a separate room or outside, and livestock were kept in a separate area,” she says. “The change in lifestyle and climate is reflected in a decline in morbidity.”

“Our study deals with the impact of the environment and social behavior on morbidity rates, and to do so, we examined a common disease that has accompanied humanity since inception – the ear infection,” concludes Dr. May. “Understanding how diseases appear, spread and disappear throughout human history can help prevent and find solutions to contemporary illnesses. The study clearly points out risk factors and shows how lifestyle changes can affect the incidence of the disease. In both ear infections and COVID-19, social distancing and adherence to hygiene reduced the spread of infection, while close quarters and unhygienic living conditions saw infections spike.”

Anthropology, Biohistory, Medicine & Health

Pursuing the Unknown

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