It cannot be produced by contamination.

It can only be produced by having a Neanderthal parent and a Denisovan parent.

The researchers also analyzed what is called “heterozygosity” — the degree to which the two copies of each chromosome differ from each other — across Denny’s genome.

In a typical individual from a single population, heterozygosity reflects the normal level of genetic diversity within that population.

In a first-generation hybrid between two distantly related populations, heterozygosity is dramatically elevated, because the two copies of each chromosome come from populations that have been diverging for hundreds of thousands of years and have accumulated many differences from each other.

Denny’s heterozygosity was, as expected, dramatically elevated.