My brother and I are fraternal twins—at least, that’s what I believed for my entire life. Growing up, we were told we shared everything: a birthday, a childhood, a bond that only twins could understand. Recently, just for fun, we decided to take one of those DNA tests.

We were curious about what similarities and differences we might have, since fraternal twins only share a portion of their genetics, like regular siblings. But when the results came in, they showed 0% genetic match. I stared at the screen, thinking it had to be some sort of glitch.