The blue eye gene in Siompu is autosomal recessive. It can hide for two or three generations, then suddenly appear in a grandchild who inherits the hidden gene from both parents.
The colour does not come from a blue pigment either, but from a low amount of melanin in the iris, so that light scatters through a physical phenomenon called Rayleigh scattering. The same mechanism that makes the sky look blue.
The question is: how did the ancestors of Siompu know?
How, hundreds of years ago, long before genetics was discovered, long before the words "recessive gene" were first spoken by Gregor Mendel in 1866, could someone already predict that this trait would skip generations and return in the seventh descendant?
Was it merely a coincidence of remarkable precision?
Or does the collective memory of a people hold biological observation, passed down not as a scientific journal but as a story?
