At any given point in time, the Neanderthal population of Eurasia probably numbered in the tens of thousands.

The Denisovan population was perhaps similar.

Over the hundreds of thousands of years that both groups existed, the total number of individuals is immense — hundreds of millions of individual lives, most of which left no trace at all.

Of this vast population, the ancient DNA evidence covers perhaps a few dozen individuals with significant genomic data.

The probability of finding a first-generation hybrid in this tiny sample is extremely small — and yet we found one.

This suggests either that first-generation hybrids were very rare (in which case finding Denny was an extraordinary coincidence) or that they were not particularly rare (in which case the probability of finding one in a sample of a few dozen is reasonable, and the implication is that such individuals were a small but non-negligible fraction of the ancient human population in contact zones like the Altai).