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## The Significance of Finding Denny, Not a Census
One of the most important cautions in interpreting the Denisova 11 finding concerns what it does and does not establish about the frequency of Neanderthal-Denisovan encounters and hybrid individuals.
Denisova 11 is the only first-generation Neanderthal-Denisovan hybrid identified in the fossil record. She is one individual. From one individual, it is not possible to calculate a rate, establish a pattern, or determine whether such hybrids were common or rare in the populations she came from.
The population-level evidence from paleogenomics suggests that gene flow between Neanderthals and Denisovans was real but limited. The Denisovan genomes carry traces of Neanderthal ancestry that indicate past interbreeding, but the proportion of Neanderthal ancestry in Denisovan genomes is not high—the populations were genetically distinct, with their own separate evolutionary histories spanning hundreds of thousands of years. If Neanderthal-Denisovan interbreeding had been frequent and extensive, the genetic distinction between the groups would have eroded over time, and the Denisovan genomes would show substantially more Neanderthal ancestry than they do. The fact that the two groups maintained their genetic distinctiveness over a long period of coexistence in the same broad region suggests that interbreeding was episodic and limited rather than continuous and extensive.
Finding Denisova 11 at Denisova Cave may reflect the fact that the cave is a uniquely favorable site for finding ancient DNA from any individual who happened to die or deposit material there, rather than the fact that the cave was a particularly likely location for Neanderthal-Denisovan encounters. The exceptional preservation at Denisova Cave has made it the richest source of ancient hominin genomes in the world. If other Paleolithic caves in Eurasia had similar preservation, they might also yield hybrid individuals—or they might not. The single documented case at Denisova Cave is consistent with both possibilities.