Humanity’s greatest strength has always been its ability to thrive in environments that would kill other primates. From the oxygen-thin peaks of the Himalayas to the deep waters of the Southeast Asian seas, Homo sapiens have pushed the boundaries of biological possibility.
However, as evolutionary anthropologist Herman Pontzer explains in his new book, Adaptable, evolution is not a perfectionist; it is a “tinkerer.” Nature does not always create the most efficient or safest solution; instead, it repurposes whatever biological materials are already available. This process often results in profound evolutionary trade-offs —where a new, life-changing ability comes at the cost of a significant physical risk.
The Fatal Price of Speech
One of the most striking examples of an evolutionary trade-off is the human throat. In most mammals, including our closest ape relatives, the larynx (voice box) is positioned high in the throat, safely tucked away from the digestive tract. This configuration allows animals to breathe and eat simultaneously without much risk.
In humans, however, the larynx has shifted downward. This “clumsy” placement creates a major biological vulnerability: choking. Every year, thousands of people die because their airway is easily obstructed by food or liquid.
Why would evolution accept such a lethal flaw? The answer lies in language.
“The low position of the larynx makes [speech] possible. If it’s higher up… the ability to shape that sound into words would be severely limited.”
By lowering the larynx, humans gained the ability to manipulate the shapes of the mouth and throat to create complex vowels and consonants. Our ancestors essentially decided that the social and survival benefits of sophisticated communication were worth the increased risk of accidental death.
Solving the Oxygen Crisis: Two Paths to the Mountains
When humans migrate to high altitudes, the body faces a crisis: there isn’t enough oxygen in the air. The standard biological response is to produce more red blood cells to carry what little oxygen is available. However, this comes with a heavy side effect—it makes the blood thicker, which can lead to altitude sickness, headaches, and even fatal fluid buildup in the brain or lungs.
Different populations have evolved different “fixes” for this problem:
- The Andean Approach: Populations in the Andes Mountains have adapted by developing larger lungs and rib cages. However, they still rely on high red blood cell counts, meaning many still suffer from chronic mountain sickness.
- The Himalayan Approach: Himalayan populations have found a more elegant, though different, solution. They carry a specific gene variant (the EPAS1 allele ) that prevents their red blood cell counts from skyrocketing. This allows them to live at high altitudes without the dangers of thick blood.
The Genetic Mystery: Interestingly, the Himalayan advantage didn’t evolve from scratch. Evidence suggests this gene was acquired through interbreeding with Denisovans, an extinct human relative. What was once a “neutral” piece of DNA from an ancient encounter became a vital survival tool when humans began moving into the mountains.
The Human “Submarines”: The Sama People
While some humans adapted to the thin air of the mountains, others adapted to the crushing depths of the ocean. The Sama (or Bajau) people of Southeast Asia live a maritime lifestyle, often spending hours a day underwater foraging for food.
To survive these dives, the Sama have undergone a unique cardiovascular adaptation involving the spleen. In most mammals, the spleen acts as a “reserve tank” for red blood cells; when you dive into cold water, the spleen contracts, injecting a fresh supply of oxygenated blood into the system.
Through natural selection, the Sama have developed a genetic mutation in the PDE10A gene that results in significantly larger spleens. This biological “extra tank” allows them to stay underwater longer and more frequently than the average human, turning a hunter-gatherer lifestyle into a specialized aquatic existence.
Conclusion
Human biology is not a finished masterpiece, but a collection of ingenious, often imperfect, compromises. Whether it is the ability to speak, to breathe in the mountains, or to dive in the sea, our most remarkable traits are often the result of nature making the best of a difficult situation.
