Due to an odd quirk of genetics and some unique evolutionary circumstances, two humans who lived at different times in the distant past managed to pass on a very small fraction of their genomes to you. And to me. To all of us.

Ayla Gavins is the principal of the Mission Hill K-8 School in Boston’s Mission Hill district. Originally from a small town near the Pittsburgh area, Ayla began her education career in the Wayland (MA) Public Schools system,...