Genetically, individuals with two X chromosomes develop as females; individuals with one X and one Y chromosome develop as males.

In ancient DNA work, the ratio of reads mapping to the X chromosome versus the Y chromosome can distinguish between these two patterns, even from fragmented, degraded genetic material.

The signal is unambiguous when sufficient data exists — and in this study, the signal was unambiguous for all 64 individuals.

All 64 were genetically male.

Why That Finding Matters

The result that all 64 analyzed children were genetically male is significant in part because of what it tells us directly, and in part because of what it suggests about the ritual context in which these children were interred.

Prior to genomic analysis, the sex of juvenile skeletal remains from Mesoamerican archaeological contexts has often been assigned through osteological assessment — the visual and metric examination of bones for features associated with biological sex.