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Inflammation of the middle ear (otitis media) comprises a group of disorders that are highly prevalent in childhood, and indeed are amongst the most common disorders of childhood. Otitis media is also heritable, and has effects on fecundity. This means that otitis media is subject to evolution, yet the evolutionary selection forces that may determine susceptibility to otitis media have never been adequately explored.

Here I undertake a critical analysis of evolutionary forces that may determine susceptibility to middle ear inflammation. These forces include those determining function of the middle ear, those affecting host immunity, and those affecting colonization by, and pathogenicity of bacteria. I review existing mathematical evolutionary models of host-pathogen interaction and co-evolution, and apply these to develop a better understanding of the complex evolutionary landscape of middle ear infection and inflammation in humans. This includes an understanding of factors determining the transition between stable evolutionary strategies for host and bacterial pathogens. This understanding will be later applied to analysis of otitis media in indigenous populations.

In the second part of this article, I apply the approach of population genetics to devise a new theory for the high prevalence of otitis media in certain indigenous populations: the Australian Aborigine, the Native American, the Inuit, and the Maori. I suggest that high prevalence in such groups may have occurred as a result of colonization of these previously isolated populations by European immigrants in the 15th and 16th Centuries. This exposed them to new strains of bacteria to which their immune system had not evolved immunity, perturbing a previously stable host- pathogen co-evolutionary state.