Most ancient humans left no recoverable trace.

Most bone fragments from cave sites were never analyzed.

The probability of finding any single individual is vanishingly small.

From another perspective, the signal of Denisovan ancestry in Neanderthal genomes (and of Neanderthal ancestry in Denisovan genomes) that researchers had found before Denny suggests that gene flow between the two groups was real but perhaps not continuous.

The statistical analysis of the signals in those genomes suggested that the interbreeding events were relatively infrequent — not a daily occurrence across all members of both populations, but occasional encounters that left detectable genetic signals.

Denny’s existence is consistent with this picture.