The ancient genomes also revealed that Neanderthals and Denisovans mixed with the direct ancestors of present-day people after they came out of Africa. So if your roots are in Europe or Asia, between 1 and 2 percent of your DNA comes from Neanderthals, and if you are from Papua New Guinea or other parts of Oceania, an additional 4 percent of your DNA comes from Denisovans.

There is much we can learn from these genetic contributions, which have consequences for how people look and what diseases they contract today. But there are lines this research should not cross: Some scientists, including George Church, a professor of genetics at Harvard Medical School, have suggested that one should consider using the Neanderthal genome sequence to genetically engineer human stem cells to produce Neanderthal embryos that can then be implanted in a woman (or a female chimpanzee) to re-create Neanderthal individuals.

This is what made me think about my grandfather. Yes, I carry some of his genetic material, and I am curious about what he was like. But would I want to exhume his bones and use the techniques we have developed to help create a “monozygous twin” of him that would be born 95 years after his death?

Since my answer is clearly no, why would it be different for a Neanderthal? Neanderthals were sentient human beings, after all. In a civilized society, we would never create a human being in order to satisfy scientific curiosity. From an ethical perspective it must be condemned.

Besides, would it even be technically possible? Although ancient genome sequences are now extraordinarily accurate, they cover only about two-thirds of the Neanderthal genetic map. The remaining third is made up of sequences that exist in two or more copies in the genome. Since the DNA preserved in ancient bones has degraded into short pieces, we cannot tell from which copies of these repeated sequences they come and so we cannot reconstruct exactly how they were arranged in the Neanderthal genome. Frustratingly, these repeated sequences may be very important for how our genome functions. So our “genetic recipe” is incomplete and will most likely always remain so.