Note this is a question from a lay reader.
I've read in the popular press that ~1-4% of the genome of non-African Homo sapiens is inherited from Neanderthals, or that Melanesians derive a similar amount from the Denisovans.
This seems like a lot, until you read (elsewhere!) that Neanderthals are 99.7% identical to humans, so most of the fraction inherited is identical in any case.
Or taking it another way, reading that two individuals will typically have 99.9% identical DNA seems pretty similar, until you realise you are only 0.3% 'different' from a Neanderthal, or 15% 'different' from your dog.
It seems to me this use of percentages is confusing, misleading, and open to abuse. When comparing species (for example) I would think that they should speak of differences in terms of base pairs that we could not otherwise have had.
How should the lay (or popular science) press best communicate similarities or differences in genomes when talking about individuals, races, or species?