Ancient DNA from people in Europe 34,000 years ago is helping scientists understand early multiple sclerosis (MS), a neurological disease affecting the brain and spinal cord. Certain genetic traits, now linked to a higher risk of MS, initially protected against diseases from animals. Scientists studied the DNA of 1,664 ancient individuals in Western Europe and Asia, comparing it to the DNA of over 410,000 modern individuals. Around 5,000 years ago, during the Bronze Age, nomadic herders called the Yamnaya people in Ukraine and southern Russia had genes that defended against infections from their livestock. However, as hygiene improved, these genes increased the risk of MS, especially in Northern Europeans, where MS is more common. This study shows that genetic traits, once helpful, can become harmful over time, suggesting MS might come from the immune system adjusting to historical challenges. The research challenges common ideas about MS and offers insights into European traits. It emphasizes the importance of adjusting, not suppressing, the immune system in treatment, with broader implications for understanding and addressing MS by considering how the environment affects genetic traits.