Sapiens Women preferred Neanderthal men

Genetic data reveal a surprising asymmetry in pairings, with a biological legacy we still carry today

A study published in Science has uncovered a fascinating insight into encounters between our ancestors and Neanderthals, painting a compelling picture of interactions between the two human species.

The findings suggest a surprising dynamic: women of Homo sapiens paired more frequently with males of Homo neanderthalensis, while unions between sapiens men and Neanderthal women were far rarer.

This isn’t a modern psychological conclusion, but a trend reconstructed from genetic data. The analyses show that attractions and pairings leading to offspring were strongly asymmetric. According to the study, numerous sapiens women gave birth to children fathered by Neanderthal men, while only a few Neanderthal females conceived children with sapiens men. Those robust, muscular individuals nonetheless left a profound mark on our biology: a portion of the European population still carries traces of their genetic heritage in their veins today.

Homo sapiens emerged in Africa around 300,000 years ago, with modern anatomy and advanced symbolic capacities. Between 60,000 and 40,000 years ago, they began expanding into the Near East and Europe, where they encountered Neanderthals. The latter were our closest relatives: adapted to cold climates, they had sturdy builds and brains comparable in size to ours. The encounter between the two species involved not just competition, but also genetic admixture. Today, we know that non-African human populations retain between 1% and 2% Neanderthal DNA.

In our genome, however, there are regions almost entirely devoid of this heritage: the so-called “Neanderthal deserts.” The most striking anomaly concerns the X chromosome, where Neanderthal-origin genetic fragments are extremely rare.

The new study, led by geneticist Sarah Tishkoff, proposes an explanation different from those hypothesized so far. It wasn’t just natural selection that eliminated these sequences, but also an imbalance in pairing patterns between the two populations.

From this perspective, evolution depends not only on environmental pressures, but also on preferences, behaviors, and social dynamics. We don’t know what factors made unions between sapiens women and Neanderthal men more frequent: power dynamics, migrations, or group structures may have played a role. In any case, courtship and attraction mechanisms helped shape the modern human genome.

The Neanderthal legacy is far from negligible. A significant portion concerns the immune system: some genetic variants helped our ancestors combat new pathogens, but today they can be linked to increased allergy risk. Other sequences influence keratin production and ultraviolet response, contributing to traits like skin tone, epidermis thickness, and hair structure.

The metabolism also bears traces of this heritage: some variants favored efficient energy storage, advantageous during food scarcity but now sometimes associated with obesity risk. Variants related to blood clotting and neurobiology have also been identified, potentially affecting sleep-wake cycles, pain perception, and stress response.

Physically, differences between the two species were evident. Neanderthals had an elongated skull, pronounced brow ridges, and a broad nose; their bodies were short, stocky, and particularly suited to retaining heat in cold climates. Sapiens, by contrast, had a more globular skull, high forehead, prominent chin, and a more slender build adapted for endurance and long-distance travel.

Despite these differences and competition for resources, Neanderthals didn’t simply vanish from the evolutionary stage. Their extinction was likely the result of multiple factors—climate changes, demographic pressures, and genetic integration with sapiens. In a sense, then, they didn’t disappear entirely: a part of them continues to live within us.

This article was originally written for the “Terra Medica” column written by Prof. Antonio Giordano for “La voce di New York“.