Altitude sickness comes from lack of oxygen in the atmosphere, but lack of oxygen can cause other complications.
Despite this, some specific populations across the globe compensate through biochemical specialisations in the way their bodies operate. This is particularly obvious in tribes living the Andes or high up on the Tibetan plateau, some 4000m above sea level, where the air only contains 60% as much oxygen as at sea level. These adaptations are generally acquired through natural selection favouring those in the original population who, through natural variation, are built to cope slightly better than others. Over thousands of years this leads to the evolution of coping mechanisms, although the coping mechanism evolved by a population in the southern Andes may not be the same specific change as that evolved by a tribe in the northern Andes.
An example of this phenomenon can be seen in the appearance of blond hair, which evolved twice as our species, Homo sapiens, spread across the globe from around 100 000 years ago: in Europeans several modified genes contribute to producing blond hair in a person, whereas Solomon Islanders also have modifications in another gene which remains unchanged in Europeans with blond hair.