This is a research method that uses genetics to help figure out whether one thing actually causes another—rather than just being linked to it. Because our genes are randomly assigned at birth (like a natural lottery), they can act like a built-in experiment. For example, if people with a gene that leads to higher vitamin D levels also have lower rates of a certain disease, scientists can use that information to see if vitamin D might really help prevent that disease. It helps reduce confusion caused by outside factors that might otherwise influence study results.