Final answer:
Some Melanesian groups share about 3-5% Denisovan and 2.74% Neanderthal DNA, but these estimates might not account for potential contributions from unknown extinct hominins.
Step-by-step explanation:
The approximate percentage of genes shared with Neanderthals and Denisovans by some Melanesian groups was originally thought to be about 3-5 percent Denisovan and 2.74 percent Neanderthal. However, research by Ryan Bohlender and his team suggests that this may not be the complete story and that there could be additional extinct hominin ancestry, possibly from a 'ghost population'. Current studies also indicate a genetic link showing that Neanderthals and Denisovans were more closely related to each other than to modern humans and that interbreeding among these groups did occur. This interaction has left a genetic signature in modern populations, indicating a complex tapestry of ancestry that includes contributions from these ancient relatives.