Why Me? Could Crohn's Disease Be an Unexpected Legacy of Our Ancestors?

Note: I found this idea fascinating. No implications for treatment or prevention.

If you have Crohn's disease, you may have wondered, "Why me?" Why does my immune system attack my own intestine? An interesting theory suggests that part of the answer may lie thousands of years in our past. Some of the genes that increase our risk of inflammatory diseases today may have helped our ancestors survive deadly infections.

During human evolution, infectious diseases were a major cause of death. People carrying genes that produced more effective immune responses were more likely to survive and pass those genes to their children. Over generations, these protective genetic variations became more common. But there was a potential downside. An immune system that was particularly effective at fighting infections might also be more likely to produce excessive inflammation under different circumstances.

A fascinating example comes from research on the Black Death, the plague that killed millions of Europeans in the 14th century. Scientists studying ancient DNA identified a variation in an immune-related gene called ERAP2 that may have improved survival during the plague. Interestingly, this same genetic variation has been associated with an increased risk of Crohn's disease today.

Although the historical evidence remains debated, the finding raises an intriguing possibility: some of the genetic susceptibility to Crohn's disease may be the evolutionary price our ancestors paid for surviving deadly infections.

This doesn't mean Crohn's disease is simply an overactive immune system or that genetics alone determines who develops it. Crohn's is a complex disease involving genetic susceptibility, intestinal bacteria, environmental influences, and abnormal immune responses. Nor does this evolutionary theory suggest any new treatment or way to prevent the disease. It is simply an interesting possible answer to the question, "Why me?" Some of the genes that contribute to Crohn's disease today may be the very genes that helped our ancestors survive centuries ago.

Based on David Quammen's article, "Where Do Autoimmune Diseases Come From?" published in The New York Times, October 20, 2026.