A common modern-day infection may have been at the crux of the rapid extinction of Neanderthals, new research suggests.
Since the official recognition of the first Neanderthal fossil in 1856, the scientific community has long wondered what killed off the species 40,000 years ago. Theories ranged from devastating tropical diseases to a cataclysmic ice age induced by climate change. Now, new research published in The Anatomical Record suggests a less dramatic, yet equally as deadly, culprit: the common ear infection.
"Neanderthals are important as they serve as a large mirror of us," study author Anthony Pagano told IFLScience. "Neanderthals and Homo sapiens (modern man) experienced [a] parallel evolutionary process on different continents – Homo sapiens in tropical Africa and Neanderthals in temperate Eurasia. Knowing the source of these differences may well bring us a greater understanding of modern man."
Physical anthropologists and head and neck anatomists reconstructed the cartilaginous eustachian tube (CET) of Neanderthals using bony landmarks from a human growth series of more than 300 skulls. Serving as a connection between the middle ear and the postnasal airway, the CET is a vital component of the upper respiratory tract and is “integral to normal physiological functions” like aeration through the middle ear and pressure equilibration. When compared against modern human skeletal structures, the CET of Neanderthals was much flatter and indicative of those found in modern infants, making it more prone to locking in otitis media bacteria responsible for ear infections. Although it's difficult to say for certain which microbe is the culprit, evidence of bony lesions inside the ear canal are a hallmark of the disease process associated with otitis media.
In modern adults, the CET takes on a more angular shape that protects the inner ear from the bacteria. Neanderthal CETs did not change with age and their infections could get worse, resulting in respiratory infections, hearing loss, and pneumonia. The infection itself likely would not have killed the Neanderthals directly. Rather, anthropologists speculate that it would have affected their ability to compete for survival, contributing to their overall extinction.
"It's not just the threat of dying of an infection," said coinvestigator Samuel Márquez in a statement. "If you are constantly ill, you would not be as fit and effective in competing with your Homo sapien cousins for food and other resources. In a world of survival of the fittest, it is no wonder that modern man, not Neanderthal, prevailed."
Researchers were drawn to studying the nasopharynx because, with every great evolutionary change in mammals (and more specifically to primates), changes in the nasopharynx have been observed.
Until now, the role of CET morphology and Neanderthal health and disease was understudied, but the authors note that understanding how the middle ear functioned in this early species of hominid can help us to understand how our own species evolved.
"The Neanderthals are our closest cousins and therefore anything that affects them would have affected us in some way," said Pagano. "Knowing why we survived and Neanderthals didn't can inform understanding of our own adaptability as a species. How did we outcompete a highly intelligent and highly resilient member of our family."