The Biggest Mystery of Ancient Human Evolution

Neanderthals have long been regarded as stone age barbarians, at least when compared to their modern human counterparts with whom they competed for food, territory and mates. Evolutionary biologist Nicholas Longridge of the University of Bath in England suggests that an aggressive military strategy is also a good evolutionary strategy. Indeed, modern humans have a history of aggressive territorial expansion. For more than a century, we regarded Neanderthals as inferior to Homo sapiens. More recently, the pendulum has gone the other way and they are widely seen as our relatives, not quite human but close enough but still not equal. Now, because to an ongoing revolution in paleoanthropology, we can see that they are something quite distinct and that they should be understood on their own terms rather than in comparison to us. The Neanderthals had their own histories, rituals and customs, and their intelligence is considerably different from ours, though not inferior, but why would our ancestors eliminate their evolutionary relatives? In his recent book, The Naked Neanderthal, Ludovic Slimac, paleoanthropologist at the University of Toulouse in France, wrote that The Neanderthal can't be equated with anything known to us. They are not our brothers or cousins. What's more, mating between Neanderthals and modern humans may have been the result of failed alliances. When two groups are close but quite different, either because they speak different languages and have different traditions or because they live in neighboring territory, they will trade women. But when you try to extract DNA from the Neanderthal fossils, there isn't a single one with sapiens' DNA. When we look at what happened during this interaction, we can see that all Homo sapiens have Neanderthal DNA, but no Neanderthals have any Homo sapiens' DNA. This is a critical issue in understanding Neanderthal extinction and the precise relationship of the two groups, says Slimac. According to a recent study, a group of humans left Africa between 250,000 and 270,000 years ago. They were sort of the cousins to all humans alive today, and they were much more like us than Neanderthals. Extinction may occur when two populations are in conflict, when there's a total war between populations, and one group is going to seek to destroy another group. And in that scenario, you regard the other group as no longer human. You will slaughter everyone and capture the children and women, according to Slimac. Far from being peaceful noble savages, Neanderthals were skilled hunters and dangerous warriors, rivaling only modern humans. Neanderthal males were skilled big-game hunters, using thrusting spears to hunt prehistoric megafauna such as cave bears and lions, jaguars, giant elephants, and woolly rhinos and mammoths. It defies belief that they would have hesitated to use their weapons if their families and territories were under threat. Indeed, territoriality is deeply ingrained in humans, an ancient and fundamental aspect of our humanity. The fact that we interbred with the Neanderthals proves that they vanished only after encountering modern humans. According to a new study, Homo sapiens men effectively emasculated their big-headed rivals when they mated with Neanderthal women sometime between 100,000 and 370,000 years ago, with a median date of 235,000 years. These unions caused modern Y-chromosomes to spread through subsequent generations of Neanderthal males, eventually replacing the Neanderthal Y-chromosome. It is well established that Neanderthals influenced the genetic makeup of modern people, but there was also a reciprocal trade. The Neanderthal population that our species encountered in Eurasia approximately 45,000 years ago already possessed certain Homo sapiens genes, which were remnants of previous encounters that occurred long ago. Based on a recent study titled the Homo sapiens Y-chromosome totally replaced the original Neanderthal Y-chromosome during early biological interactions that occurred approximately 370,000 to 100,000 years ago. You may remember from biology class that men inherit the Y-chromosome from their fathers. In fact, they get a nearly identical copy with only a few mutations. This means that the Y-chromosome does not change significantly from generation to generation. So imagine a single battle wiping out an entire clan of men who share the same Y-chromosomes, then repeat the scenario many times over course of generations. The victorious clans would win battles and expand, resulting in a loss in Y-chromosome diversity. In fact, dominant males associated with these events may be responsible for the Y-chromosome patterns we observe today. The Neanderthals were the first large-brained humans to occupy Europe, and while they left some genetic legacy, later waves of humans are responsible for the majority of modern European ancestry. The first anatomically modern humans arrived on the continent approximately 50,000 years ago. These were the Paleolithic hunter-gatherers, also known as Cro-Magnons. They populated Europe sparsely and lived a lifestyle similar to the Neanderthals they replaced. Then, approximately 5,000 years ago, the Y-chromosome in Europe was mostly replaced by an invading group. The population replacement occurred during the Bronze Age, which saw changes in cultural practices, the spread of horseback riding, and advancements in weaponry. Did early Homo sapiens also replace the Neanderthal Y-chromosome during an ancient conflict? The incompleteness of the fossil record makes it difficult to test these hypotheses. However, fossils from Europe, the only place with a relatively complete archaeological record, show that Neanderthals disappeared within a few thousand years of our arrival. Most of what we know comes from the DNA of our regular chromosomes. There is less information on sex chromosomes. Geneticists can use these DNA differences to determine when two populations, such as Homo sapiens and Neanderthals, last shared a common ancestor. We can count the small differences in their DNA, and compare them to the rate at which human DNA accumulates mutations to get a rough estimate of when the populations split. The DNA data from the non-sex chromosomes show that Neanderthals and Denisovans are related to a branch of the human family tree that split off from ours between 700,000 and 550,000 years ago. But the Y-chromosomes tell a different story, indicating that our most recent common ancestor lived approximately 370,000 years ago. In the not-so-distant past, our species shared the planet with at least two other closely related hominins. The tools, beads, and art they left behind indicate that these other humans were likely similar to us, and we were definitely enough alike to have some sexual relations. This resulted in a complex population history spanning thousands of years and multiple continents. As stated according to a new study, early Homo sapiens men emasculated their brawny cousins when they mated with Neanderthal women over 100,000 years ago. These unions caused modern Y-chromosomes to spread through subsequent generations of Neanderthal males, eventually replacing the Neanderthal Y-chromosome. The new discovery may answer the decade-long mystery of why researchers have been unable to locate a Neanderthal Y-chromosome. Part of the problem was a lack of DNA from Neanderthal males. Of the dozen Neanderthals whose DNA has been sequenced so far, the majority are female, as the DNA in male Neanderthal fossils was either poorly preserved or contaminated with bacteria. The researchers examined the fragmentary Y-chromosomes of three Neanderthal males from Belgium, Spain, and Russia who lived 38,000 to 53,000 years ago as well as two male Denisovans, close Neanderthal cousins who lived in Siberia's Denisova Cave between 46,000 and 130,000 years ago. When the researchers sequenced the DNA, they discovered a surprise. The Neanderthal Y-chromosome looked more like modern humans than Denisovans. This was puzzling because previous research had shown that the rest of the Neanderthal nuclear genome was more closely related to Denisovans. The study also discovered that Denisovan Y-chromosomes split around 700,000 years ago from a lineage that included Neanderthals and modern human Y-chromosomes which diverged around 370,000 years ago. This suggests that the two groups diverged from modern humans approximately 600,000 years ago. Nevertheless, the appearance of the unusual Y-chromosome corresponds to another genetic takeover. The study hypothesizes that the human Y-chromosome may have provided a slight fitness advantage over their Neanderthal counterparts. Because Neanderthals had a smaller population size than humans, they most likely accumulated more deleterious or harmful mutations in their genome, particularly on the sex chromosomes. According to computational models, the most plausible explanation for the Y-chromosome pattern is that early modern human males mated with Neanderthal women more than 100,000, but less than 370,000 years ago. Their male offspring would have inherited the modern human Y-chromosome from their father. According to the researchers, the modern Y-chromosome quickly spread through their offspring to the small populations of Neanderthals in Europe and Asia, replacing the Neanderthal Y-chromosome. Maybe early modern humans were more genetically diverse, most likely possessed Y-chromosomes free of undesirable mutations. These mutation-free chromosomes may have provided a slight genetic advantage, allowing them to out-compete Neanderthal's Y-chromosome. According to scientists, modern humans' larger, more genetically diverse ancestral populations may have provided a genetic advantage. Another possibility is that after Neanderthals inherited modern human mitochondrial DNA, their cells may have favoured interaction with the modern human Y-chromosome. Meanwhile, the study demonstrates that admixture between modern humans and Neanderthals was a defining feature of their history. Not only did it give modern humans Neanderthal DNA, but it also fundamentally altered Neanderthal evolution. But how exactly did this happen? Even after primitive Homo sapiens invaded Eurasia 200,000 years ago, it took more than 150,000 years to conquer Neanderthal territory. For what reason would we delay our invasion of Europe? The reason for this delay was not due to the inhospitable environment, but rather because Neanderthals were already dominating Europe and nearby regions. According to the evidence of early Homo sapiens fossils from Greece, archaic Homo sapiens gained ground, only to be driven back by Neanderthal counter-offensives 200,000 years ago before a final offensive by modern Homo sapiens, which began 60,000 years ago, eliminated them. Indeed, Apidema I was dated to 210,000 years ago, making it by far the oldest Homo sapiens fossil found on the continent and a possible member of the group that wiped out the Neanderthal male chromosome. Neanderthals were very similar to us. Our skull and skeletal anatomy are remarkably similar and 99.7% of our DNA is the same. Neanderthals behaved remarkably similarly to humans. They built fires, buried their dead, fashioned jewelry out of seashells and animal teeth, and created cave art and stone shrines. If Neanderthals shared many of our creative instincts, they most likely shared many of our destructive instincts as well. Their massive, muscular builds must have made them formidable fighters in close-quarters combat. Neanderthals' large eyes most likely provided superior low-light vision, allowing them to maneuver in the dark for ambushes and dawn raids. Prehistoric battle strategies favored raids and ambushes in which adult males captured by an enemy were almost always eliminated. Romantics have portrayed early hunter-gatherers as peaceful, noble savages. However, historical accounts and archaeology all show that conflict in primitive cultures was intense, widespread, and lethal. Therefore, it is highly unlikely that modern humans met the Neanderthals and decided to simply live and let live. There is little reason to believe that early Homo sapiens were less prone to conflict and less territorial. Nevertheless, the interaction between Neanderthals and sapiens was not one of good versus evil. And with that tantalizing statement, we leave you to ponder the mysteries of our human history. Until next time, stay curious and stay questioning. Please subscribe, share, and check out other highly compelling videos on our channel. Thank you and take care.