Two million to 3 million years ago, a mutation in human ancestors inactivated a gene preventing artery clogging, which may explain humankind’s increased risk of experiencing heart problems compared with other species, The Guardian reports. This has stumped scientists for ages, but new research may explain why. Researchers genetically modified mice to inactivate a gene called CMAH, which may have helped humans become long-distance runners. CMAH also makes a sugar molecule called N-Glycolylneuraminic acid (Neu5Gc), which leads to chronic inflammation in modern humans. The modified mice had nearly double the rate of artery clogging compared with controls, and it got even worse when they ate a high-fat diet that reintroduced Neu5Gc to their systems. The findings suggest a genetic trade-off occurred uniquely in humans with the loss of Neu5Gc, the researchers report this week in the Proceedings of the National Academy of Sciences.