How they engaged in intimate relations

Picture yourself in 50,000 BC, where the biting cold wind swirls around your Neanderthal form as you seek warmth beside your companion for the day. "Nia," you murmur softly, and she responds, "Oh Dag," as she melts into your embrace. You both dive into the moment, oblivious to the fact that she is, in fact, your cousin. Life for Neanderthals was undeniably harsh and wildly unpredictable, particularly in matters of intimacy. These tumultuous romantic entanglements may have played a role in their eventual decline, a phenomenon humorously dubbed "sextinction."

Neanderthals often conjure images of stocky, muscular beings with distinctive sloped foreheads, and while that's mostly accurate, the hairiness is a bit exaggerated. These robust figures were surprisingly social, with evidence suggesting they had more romantic partners than early humans. However, their mating habits were heavily influenced by the seasons. During the colder months, when food was scarce, Neanderthals tended to settle down with a single partner, engaging in what could be likened to a cozy night of cave painting and relaxation.

As summer arrived, their dynamics shifted dramatically. With the clan able to stay close together, free from the constant search for sustenance, the Neanderthals embraced a more liberated approach to relationships, leaving their options wide open.

This indicates increased interactions among various Neanderthals. Dag suddenly realizes that his cousin Mara has been looking quite attractive lately. It's interesting since she belongs to his mother's side of the family, unlike Nia. The dynamics of this Neanderthal love triangle, filled with relatives, will be clarified later. With the ability to gather food for a larger group and the presence of nearby Neanderthals to assist, Dag feels motivated to pursue Mara as well. Researchers suggest that the multiple notches on the cave wall relate to the digit ratio theory, which posits that higher testosterone levels typically result in a longer ring finger. Consequently, scientists have concluded that a smaller gap between the index and ring fingers indicates a species that is more aggressive and competitive, particularly in mating scenarios.

Neanderthal skeletons discovered by scientists exhibit significantly longer ring fingers compared to those of early humans, leading some researchers to suggest that they may have engaged in more competitive mating behaviors. However, Neanderthals, like Dag, were still more inclined towards monogamy than their closest relatives, such as apes and chimpanzees, largely due to anatomical differences in their reproductive organs.

Neanderthals lacked the penile spines found in other large apes, which are composed of the same material as skin and hair. These spines serve to remove sperm from previous mates during copulation and discourage females from mating with other males immediately afterward due to the discomfort caused by the spines. In contrast, chimpanzees are not known for their romantic tendencies.

When humans and Neanderthals evolved separately around 600,000 years ago, both species lost their spines, leading to a collective sigh of relief from women everywhere. Neanderthals developed societies that emphasized cooperation and collaboration, which encouraged a trend toward monogamy, particularly during challenging times, even if it wasn't perfect. As a result, there was no need for spines to eliminate the sperm of rival males.

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Sexual attraction can have dire consequences, especially for Neanderthals. One theory suggests that when Neanderthals and early humans interbred, the human genes prevailed. Imagine Dag, a Neanderthal, seeking a mate beyond his relatives. He encounters Karen, a taller and slimmer human, whose features intrigue him despite their differences. Attempting to communicate proves futile, as Karen cannot understand his language. After a moment of thought, Dag gestures for her to join him in his cave, where he uses charcoal to illustrate a couple. Captivated by the drawing and Dag's physique, Karen leans in for a kiss. They share a memorable night together, but the next day, Karen returns to her clan and soon discovers she is pregnant. Having witnessed this before, she hopes her child inherits more of her traits, knowing it will enhance its chances of survival.

Neanderthals, while shorter in stature, possessed a broader and heavier physique, requiring significantly more energy to sustain themselves—approximately 600 to 700 extra calories daily compared to modern humans to support their robust bodies. As the climate began to cool around 40,000 years ago, coinciding with the Neanderthals' extinction, food sources became scarcer. This shift rendered Neanderthal genes less advantageous for survival, as children inheriting more human traits had improved survival odds, resulting in a gradual increase in human characteristics among mixed offspring. Additionally, interbreeding with humans posed further challenges for Neanderthals.

Scientists discovered a blood condition known as HDFN, or hemolytic disease of the fetus and newborn, present in both humans and Neanderthals, but it appeared to be significantly more prevalent among humans. This lack of natural immunity in Neanderthals meant that when they interbred with humans, they inherited more HDFN-related genes, resulting in higher mortality rates within their population. If the roles were reversed and a Neanderthal woman had a child, that baby would remain with the Neanderthal tribe, likely growing up to mate with another Neanderthal and perpetuating the gene. As the HDFN gene spread through the Neanderthal community, it restricted their reproductive capacity and stunted population growth, ultimately tying back to Dag's unusual familial connections with his cousins, Nia and Mara.

Research has uncovered significant evidence of inbreeding among Neanderthals, a practice that modern humans largely abandoned early on. A notable discovery at El Sidron in Spain revealed the remains of thirteen individuals, all related, including couples who were also extended family. The skeletal remains exhibited various signs of inbreeding, such as malformed knees and retained baby teeth, among other health complications. Tragically, researchers determined that these individuals met a grim fate, having been murdered and subjected to cannibalism.

The three adult males discovered were siblings, and the women were likely their partners. This suggests that Neanderthals engaged in a practice similar to many early human societies, where a woman would leave her family to join her mate's. However, unlike typical human societies, the women's DNA indicated a degree of familial connection, albeit more distant.

This occurrence in El Sidron was not an isolated incident. Evidence of similar deformities in the knees, thighs, and arms, indicative of inbreeding, has been observed in Neanderthal skeletons throughout Eurasia.

Scientists believe that, unlike European royal families, Neanderthals did not intentionally engage in incestuous relationships. The prevailing theory suggests that the limited population of Neanderthals contributed to this behavior, as there were simply not enough individuals available for mating. Factors such as fragmented groups searching for food, reduced mobility, and heightened competition with humans resulted in increasingly smaller social units. Consequently, when Neanderthals sought partners beyond their immediate relatives, their options were severely restricted. Additionally, as demonstrated by Karen, interactions with humans proved to be equally detrimental to their survival.

Social networks played a significant role in the evolution of human societies, influenced by the digit ratio theory. More monogamous individuals with lower levels of competition and testosterone tended to form larger groups, quickly recognizing the dangers of inbreeding. These expanded social circles enabled couples to have more children, as community members could assist in child-rearing while parents focused on securing food and constructing shelters. In contrast, while Karen had numerous unrelated men and neighbors to support her, Dag was likely limited to a few related women and lacked substantial assistance. This disparity resulted in fewer offspring and a higher prevalence of similar genes among Neanderthals, ultimately diminishing their chances of survival and contributing to their eventual extinction.