Too Much of a Good Thing

Imagine a world far removed from the bustling cities and technology we know today—a world where survival depended on keen instincts, physical resilience, and the slow, steady march of evolution. Our journey begins some 200,000 years ago in Africa, the cradle of Homo sapiens, where our ancestors first emerged with a unique combination of traits that would shape the course of human history. These early humans were not alone; other Homo species like Neanderthals and Denisovans roamed the earth, sometimes overlapping with our ancestors. But rather than being replaced outright, these groups interbred, leaving traces of their DNA in modern populations. About 2 percent of the DNA in Europeans and Asians comes from Neanderthals, a testament to this ancient mingling.

Our genes tell a story of survival shaped by random mutations that proved advantageous in specific environments. Natural selection favored those whose genes helped them withstand starvation, disease, and climate challenges, allowing their descendants to thrive. Yet, this process is slow—mutations spread over thousands of years, meaning our bodies are still largely adapted to a world that no longer exists. For example, skin color evolved as a delicate balance between absorbing enough ultraviolet light to produce vitamin D and protecting folate from degradation by sunlight. Dark skin protects folate in high UV environments, while lighter skin facilitates vitamin D synthesis where sunlight is scarce.

This evolutionary backdrop sets the stage for understanding why our survival traits, so finely tuned for the past, now sometimes betray us in the modern world. The pace of environmental change has far outstripped the slow rhythm of genetic adaptation, leading to health challenges we are only beginning to understand.

As we move into the next chapter, we will explore how one of these fundamental traits—our appetite and relationship with food—has transitioned from a survival advantage to a modern health crisis.