Naked mole rats are rather extreme animals in many ways. As underground dwellers, they live in chronically hypoxic environments and are blind. These animals also age more slowly than other mammals and are resistant to developing cancer even though they are long-lived.
Did you also know, they are hard of hearing? In a new study published in Current Biology, researchers have discovered the cause of their hearing loss. The inner ear contains both outer and inner hair cells. The outer hair cells are responsible for amplifying sounds (see YouTube video below). It is these outer hair cells that are damaged in mole rats. The authors speculate that mole rats evolved hearing loss because they may not need to hear as well in their underground dwellings or to lessen distractions caused by hearing echoes.
Similar to mole rats, the most common cause of hearing loss in older human adults is a loss of hair cells. This means that mole rats may be a natural animal model of hearing loss and deafness in humans.
Here is a YouTube video describing how the hair cells in our ears work:
SJ Pyott, M van Tuinen, LA Screven, KM Schrode, J-P Bai, CM Barone, SD Price, A Lysakowski, M Sanderford, S Kumar, J Santos-Sacchi, AM Lauer, TJ Park. Functional, Morphological, and Evolutionary Characterization of Hearing in Subterranean, Eusocial African Mole-Rats. Current Biology. 2020. DOI: 10.1016/j/cub.2020.08.035