Peak Isolation.

For many species, a mountain summit is more than a home—it is a biological prison. These high-altitude refuges, known as "Sky Islands," are the birthplaces of Earth's rarest evolution.

In evolutionary biology, isolation is the engine of diversity. When a population becomes physically separated from its kin, it begins to adapt to its specific environment in a process called allopatric speciation. Mountains provide this isolation vertically. A species living at 4,000 meters cannot survive a descent through the warm, humid valleys to reach the next peak, effectively trapping it on a high-altitude island surrounded by a sea of air.

The Endemism Trap

This isolation leads to high rates of endemism—species that are found in one specific location and nowhere else on Earth. On the "tepuis" (tabletop mountains) of South America or the high peaks of the Ethiopian Highlands, nearly 90% of the flora and fauna can be endemic. They have evolved specialized traits, such as unique digestive enzymes to process high-altitude plants or altered hemoglobin to thrive in low-oxygen environments.

However, this specialization comes with a high price. Because these species are so perfectly tuned to their narrow vertical slice of the world, they have nowhere to go if the climate shifts. As global temperatures rise, these species are forced higher and higher up the mountain to find their required cold. Eventually, they reach the summit. This is known as the "Escalator to Extinction"—when the mountain ends, there is nowhere left to climb.

Relicts of the Ice Age

Mountains also act as "refugia"—biological time capsules. During the last Ice Age, cold-loving species covered much of the Earth. As the planet warmed, these species retreated toward the poles and up into the mountains. Today, many mountain-top species are glacial relicts; they are the living descendants of Ice Age survivors, preserved in the high-altitude cold while the world below transformed around them.