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Picture the scene: you're sitting quietly on the couch, you've just finished eating, and suddenly you hear noises in the garden. You go over to the window to see what's going on and see an individual similar to you yet different. How would you feel?

This is exactly what happened in Western Asia, between 90,000 and 40,000 years ago, when Neanderthals first encountered a new human species. For the first time, Neanderthals encountered Homo sapiens. From this encounter, one of the most fascinating chapters in our origins would emerge, a period characterised by exchange, competition, coexistence, and... attraction.

For decades, evolutionary studies interpreted this period as an uncontrollable advance of Homo sapiens. Our species, characterised by strong adaptability to various environments and climates, colonised the entire globe in just a few tens of thousands of years (crumbs in prehistoric terms), "crushing" the Neanderthals.

The turning point came just over a decade ago, when Svante Pääbo managed to analyse the entire genome of Homo Neanderthalensis. The result? Modern Eurasian populations share between 2 and 4% of their DNA with this species. Translated, groups of Homo sapiens and Neanderthals interbred, presumably in the Ancient Near East.

In more detail, this hybridisation wasn't always so simple. In fact, genes derived from Neanderthals are integrated into our non-sex chromosomes (autosomes) but do not appear in mitochondrial DNA or the Y chromosome. These analyses imply that the union between a Neanderthal male and a Sapiens female led to genetic incompatibility (with spontaneous abortions or sterile male offspring). Conversely, interbreeding between Sapiens males and Neanderthal females produced healthy, fertile individuals.

An even more fascinating example concerns the skeleton of a Sapiens man found in Peştera cu Oase, Romania, and named Oase 1. His DNA shows a Neanderthal percentage of between 6 and 9%, meaning that his Neanderthal ancestor was only four to six generations distant (imagine a great-great-great-grandfather).

In conclusion, we can confidently state that these aliens—us—have incorporated into their modern DNA the previous humanity that lived in Asia and Europe. Neanderthals did not go extinct; they still live alongside us today.