Scientists have discovered that the prehistoric romance between Neanderthals and modern humans was a heavily lopsided affair, with pairings occurring almost exclusively between Neanderthal men and modern human women.
This discovery, published in the journal Science on February 26, 2026, challenges the long-standing belief that human evolution was driven solely by the survival of the fittest.
By analysing the genetic blueprints of both species, a team from the University of Pennsylvania led by Sarah Tishkoff and Alexander Platt has revealed that ancient attraction and social choices, rather than biological failure, are the reasons why Neanderthal DNA is missing from key parts of our genome today.
WHAT HAPPENED WHEN NEANDERTHALS AND HUMANS DATED?
Most people with non-African roots carry about two per cent Neanderthal DNA as a silent souvenir of our past.
However, scientists noticed something strange: huge sections of our X chromosome are completely devoid of this ancient ancestry.
The X chromosome is one of the two sex-determining chromosomes in humans, carrying hundreds of essential genes that influence everything from immune function to brain development.
The 23rd pair of chromosomes determines one’s sex. Males have X and Y sex chromosomes, while females have two X chromosomes.
For a long time, experts believed these Neanderthal genes were biologically toxic.
They assumed that any baby born with them would have health or fertility problems, causing nature to eventually delete those genes from the human population.
The new study from the Tishkoff Lab proves this theory wrong. The logic is simple: if Neanderthal genes were truly harmful to humans, then human genes should have been just as harmful to Neanderthals.
When researchers studied three specific Neanderthal fossils, Altai, Chagyrskaya, and Vindija, they found plenty of human DNA on their X chromosomes.
Because our genes lived on healthily in their bodies, it proves that the two species were biologically compatible after all, debunking the myth of prehistoric genetic warfare.
DID NEANDERTHAL MEN PREFER MODERN HUMAN WOMEN?
The reason for the missing Neanderthal DNA comes down to the elegant dance of how X chromosomes move from parents to children.
A mother passes one X chromosome to both her sons and daughters. However, a father only passes his X chromosome to his daughters.
If a Neanderthal man mated with a modern human woman, their son would get a Y chromosome from his father and an X chromosome from his human mother. This son would have zero Neanderthal X DNA to pass on.
Because these specific pairings produced sons with human X chromosomes, very little Neanderthal X DNA ever made it into the human population.
What about the daughters? While a daughter born to such a couple would indeed inherit one Neanderthal X chromosome from her father, she would likely remain within the human group.
Over several generations of mating with modern human men, that single thread of ancient heritage would be diluted or lost entirely through the natural shuffling of genes.
This explains why we see almost no Neanderthal traces on our X chromosomes today.
The study found that Neanderthals had 62 per cent more human DNA on their X chromosomes than expected.
This lopsided pattern suggests that Neanderthal men were the ones mainly mating with human women.
On the flip side, human X chromosome DNA flooded into the Neanderthal population through these same couples.
This was not a random accident but a persistent social habit that lasted for thousands of years, suggesting that our ancestors had a type.
WHAT DOES THIS REVEAL ABOUT ANCIENT SOCIAL LIVES?
Mathematical models confirmed that mating preferences provide the simplest explanation for the genetic patterns we see today.
This discovery moves the conversation away from biological failure and towards the complex social lives of our closest evolutionary cousins.
The team is now investigating whether these ratios can reveal deeper gender dynamics, such as whether males migrated to new groups while females stayed with their birth families.
By mapping these ancient interactions, the research proves that the rules of attraction 50,000 years ago were powerful enough to permanently alter the genetic map of humanity.
It shows that our evolution was not just a cold battle for survival, but a story sculpted by intimate social choices and prehistoric preferences that still resonate in our DNA today.
