Affecting 1 in 1,000 people, multiple sclerosis (MS) is an autoimmune disease in which the body's immune system attacks its own brain and spinal cord. The findings presented in the new paper show that many of these genetic variants provided protection against infectious diseases. This is why the immune system in all present-day individuals is also, genetically speaking, the product of selection processes our ancestors underwent. This would allow their immune system to play an active role in suppressing the disease. The paper, 'Elevated genetic risk for multiple sclerosis emerged in steppe pastoralist populations', is published in Nature.