A groundbreaking 2025 study from UT Southwestern's Children's Medical Center Research Institute (published in PNAS) reveals a surprising evolutionary advantage: losing the ability to produce vitamin C protected our ancestors from deadly schistosome parasites that cause schistosomiasis—a disease still affecting over 250 million people today.
Here’s the shocking discovery in action:
These microscopic images show Schistosoma parasites (the flatworms responsible), including eggs and adult forms that wreak havoc in the body.
The key? Schistosomes need vitamin C (ascorbate) from their host to reproduce properly—especially to develop healthy eggs.
This is the molecular structure of vitamin C itself:
In lab experiments, normal mice (which can make their own vitamin C) mostly died from severe schistosomiasis infections. But mice genetically engineered to lack the GULO gene (just like humans) survived dramatically better—only 5% died! The parasites produced far fewer, malformed eggs, starving the infection cycle.
This trade-off happened ~60 million years ago in our primate ancestors when the GULO gene was lost, turning vitamin C into a dietary essential.
Without enough vitamin C from food, humans risk scurvy—a horrific disease that plagued sailors and explorers historically.
Here are classic historical illustrations of scurvy symptoms:
The research flips the old theory that we simply "didn't need" to make vitamin C because of fruit-rich diets. Instead, this loss may have been a clever defense against parasites like schistosomes, even if it left us vulnerable to deficiency in low-vitamin environments.
This evolutionary puzzle, reported widely in late 2025 and early 2026, shows how a "disadvantage" can become a lifesaving adaptation!
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