The specific results — the assignment of the child to the Ancient Beringian population, the determination of sex, and the identification of mitochondrial lineage — were derived from the available genomic data, with appropriate acknowledgment of the limitations imposed by the quantity and quality of the preserved DNA.

The Child Was a Girl

Genetic sex determination from ancient DNA is based on the specific composition of the sex chromosomes.

Human beings have two types of sex chromosomes: X chromosomes and Y chromosomes.

Females carry two X chromosomes; males carry one X and one Y.

This difference is detectable in the ancient genomic data: male individuals show reads mapping to both the X chromosome and the Y chromosome, while female individuals show reads mapping only to the X chromosome.

When the Trail Creek ancient-genome data was analyzed, it showed the pattern expected for a female individual: reads mapping to the X chromosome but not to the Y.