What happens when you bring a chicken to the Andes? Five hundred years later, its descendants might just be suited to mountain climbing.
High-altitude ecosystems offer a natural lab for seeing convergent evolution do its dance: the mountains are a shared low-oxygen setting that affects every species living there. In the Andean Altiplani, the Qinghai-Tibetan Plateau, and the Ethiopian Highlands, this applies to wildlife, humans, and domestic animals alike. Faced with the same physiological problem, natural selection offers up different solutions.
According to a recent review, researchers have mapped out many roads that all lead to the same high-altitude adaptation destination. Most of the humans and domesticated animals studied had physiological adaptations to deal with hypoxia (lack of oxygen). But different genetic pathways have been modified to achieve this result, and functions such as development, chemical response, and stress have also undergone selection. Concentration of hemoglobin, the transporter of oxygen in the blood, illustrates this: people living in the Andes show elevated levels in general, while Tibetan humans and Tibetan mastiffs do not show increased hemoglobin levels until they are over 4000 m.
A map of all the evolutionary connections shows 15 different gene variants that assist in high-altitude living. The gene EPAS1 is shared between geographically separated populations, such as Tibetan cashmere goats and feral Andean horses. In some cases, it has been inherited through interspecies breeding: Denisovans to Tibetan humans, Tibetan wolves to Tibetan mastiffs.
Domesticated animals offer snapshots of selection in motion. Chickens introduced to the Andes less than 500 years ago already show signs of adaptation, via stronger bonding of oxygen to their hemoglobin carriers. High-altitude Ethiopian cattle thrive with oxygen saturation levels of 68%, while lowland breeds die from anything below 80%. This synthesis of the research highlights that natural selection does not always shape the same solution for a single problem, and highlights the diversity of adaptations to high altitude environments across the animal kingdom.