They don’t technically have stronger genetics—but they do have genes that come from two very different parts of the world, different enough that the people in those parts of the world are now socially defined as having come from different races.

The benefit that mixed-race folks have is greater genetic variety. From their mother they have a set of genes that came from one part of the world; from their father, they have a set of genes that came from another part. So their mother and their father are less closely related to each other than most people’s parents are.

When you inherit genes from your parents, they come in pairs. Say you got a gene from Mom for blue eyes, and a gene from Dad for brown eyes; you have brown eyes, with a recessive gene for blue that you can pass on to your kids. Most genes aren’t nearly that simple, because they don’t tend to be fully dominant or recessive like that and because they combine with and interact with other genes. The principle is the same though: One gene from Mom, one gene from Dad, and when they match up they determine together how you develop and how your body works.

Many genetic diseases and vulnerabilities only affect a person if they inherit the same, defective, gene from both Mom and Dad. Take Tay-Sachs disease, a progressive, life-limiting genetic defect. For a child to inherit Tay-Sachs, they have to get one defective gene from Dad and one from Mom. Neither parent has Tay-Sachs (they can’t; the disease is fatal before reproductive age) because they also have one normal gene that covers for the defective one. The gene for Tay-Sachs is particularly common in Jewish people from middle to eastern Europe—so when two Jewish people from that area of the world marry, they often have to get genetic tests so they can decide whether to risk having children. If they’re both carriers, their chance of having a kid with Tay-Sachs is one in four each time they have a baby.

But say your Eastern European Tay-Sachs carrier marries an Alaskan native instead. The Alaskan native has ancestry from such a different part of the world that they are extremely unlikely to also be a Tay-Sachs carrier. Other examples of such disorders are cystic fibrosis (European descent), sickle cell anemia (African descent), lactose intolerance (Native Americans), and thalassemia (Mediterranean descent).

That goes for every gene in your DNA, and you have a lot of them. Not all of them are known like the gene for Tay-Sachs; most of them have more subtle effects than that. Most disorders caused or affected by genetics are not single-gene disorders that are as simple to explain as Tay-Sachs. Regardless, because they are far less likely to get matching copies because their parentage is so diverse, mixed-race people tend to do better in the genetic lottery than most of us. When they inherit a defective gene from their parents—and they inherit just as many as anyone else—that defective gene is far less likely to match up with another defective one from the other parent.

By the way, I need to make it clear that it isn’t race that causes this effect; it’s ancestry. For example, African-Americans are often of mixed European and African ancestry; their race (a sociocultural concept) is “black”, but if you want to look at their genetics, you cannot say that they’re unrelated to Europeans. Similarly, Africa is an entire continent and you can’t lump all of the people from Africa into one ancestral group, either.

If you’re interested in genetic diversity and what happens when gene pools mix, you’ve simply got to keep those two concepts separate. Race is irrelevant to that sort of study (unless you are looking at environmental/genetic interactions, but that’s not strictly genetic). Rather, what you’re interested in is where a person’s ancestors came from before world travel became common and people started meeting those from far away.

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