Did Ancient Humans Kill the Other Human Species?

[00:00:00]There was a moment somewhere in the deep past when there was more than one kind of human on Earth. Not metaphorically, not in the sense of different ethnicities or different cultures, literally different human species, distinct biological lineages separated by hundreds of thousands of years of independent evolution, walking the same landscapes, breathing the same air, and in some cases looking across a valley at each other. At one point, researchers believe at least five or six different hominin species may have coexisted on the planet simultaneously. Homo sapiens, Neanderthalss, denisovvens, homo florosensis, the smallbodied species found on the Indonesian island of Flores, nicknamed the hobbit because paleontologists apparently enjoy a good Tolken reference. Possibly Homo Lusanis from the Philippines. Possibly others we haven't found yet. Today, there is one, just us, homo sapiens, alone on a planet that used to be considerably more crowded with beings who thought, made tools, used fire, buried their dead, and in at least some cases, created art.

[00:01:11]What happened to the others is one of the most contested, most emotionally charged, and most scientifically fascinating questions in the entire field of human evolution. And the answer, the real evidence-based, as honest as the record allows answer, is significantly more complicated and more uncomfortable than most popular accounts suggest. Let's go through it properly.

[00:01:33]Start with the most dramatic framing because it is the one that dominates popular consciousness and needs to be taken seriously before it can be evaluated accurately. Did modern humans kill the Neanderthalss?

[00:01:46]The question carries an implicit weight that goes beyond paleontology. If the answer is yes, if our species deliberately, systematically eliminated other human species, that is not just an interesting historical fact. It is a statement about what humans are, about the depth of our capacity for violence and about whether what looks like progress might at its deepest root be built on something we would rather not think about. So, let's look at the evidence. Neanderthalss lived across Europe and Western Asia for approximately 400,000 years. They were not primitive in the sense that the word is casually used. Their brains were as large as ours. In some specimens larger, they made sophisticated tools, the mustisterian tool industry associated with Neanderthalss shows specific manufacturing techniques that required planning and skill. They cared for their injured and elderly. There are Neanderthal skeletons showing healed injuries that would have required weeks or months of dependent care to survive.

[00:02:47]They buried their dead. Some evidence suggests they decorated themselves and possibly produced rudimentary art, though this remains contested. They were not cognitively simple creatures encountered by a vastly superior invader. They were people by any reasonable definition of the word with complex lives, social structures, and behavioral repertoires.

[00:03:09]And approximately 40,000 years ago, shortly after modern humans arrived in Europe in significant numbers, they disappeared. The correlation is stark.

[00:03:18]Modern humans arrive in a region. Not long after, the Neanderthalss in that region are gone. This pattern repeats across the geographic range of Neanderthal habitation. It is not subtle. It is exactly what you would expect to see if modern human arrival was causally connected to Neanderthal disappearance. But correlation is not causation. And the history of paleoanthropology is littered with confident conclusions that subsequent evidence dismantled. So what are the actual proposed mechanisms and what does the evidence say about each? The direct violence hypothesis is the most dramatic and the one that captures popular imagination most effectively.

[00:03:57]Modern humans and Neanderthalss met, fought, and modern humans won. genocide or something functionally equivalent to it carried out over thousands of years across a continent. The evidence for direct violence is limited and contested. There are Neanderthal skeletal remains showing trauma that some researchers attribute to violence from modern humans. But distinguishing violence caused by modern humans from violence caused by other Neanderthalss, from accidents, or from post-mortem damage by geological processes is genuinely difficult. There is no clear smoking gun evidence of systematic large-scale inner species violence in the fossil record. That absence is not proof of innocence. Violence between ancient humans leaves ambiguous traces in bone. And large-scale population elimination through violence that happens over thousands of years spread across a continent would not necessarily leave obvious concentrated evidence at any specific site. The absence of clear evidence is consistent with both it happened but the evidence didn't survive and it didn't happen in the way the genocide hypothesis proposes. What we do have is evidence of interaction. And here is where the story becomes significantly more complicated and depending on how you feel about it, either more unsettling or more human.

[00:05:22]Neanderthal DNA is in your genome right now, not as a distant trace detectable only with sophisticated equipment as a measurable, functionally significant percentage of the DNA of every non-African modern human alive today.

[00:05:38]Between 1 and 4% of the genome of people with ancestry outside of subsaharan Africa is Neanderthal in origin with some populations particularly in East Asia and Oceanania showing slightly higher percentages. This means that modern humans and Neanderthalss interbred repeatedly across thousands of years at multiple geographic locations, producing offspring who survived and reproduced and passed Neanderthal genes down through generations until those genes appear in your cells today.

[00:06:08]Implications of this for the question of whether modern humans killed the Neanderthalss are complicated.

[00:06:15]Interbreeding is not compatible with pure total war. groups that are engaged in systematic mutual extermination do not also produce viable offspring together. At minimum, the relationship between modern humans and Neanderthalss included periods of proximity and interaction that were, let us say, not uniformly hostile. But interbreeding also raises its own complications. The Neanderthal genetic contribution to modern human genomes is present but relatively small and it appears to have been introduced in a relatively limited number of interbreeding events rather than through continuous extensive mixing. This pattern is more consistent with occasional contact between populations that were mostly separate than with the kind of sustained large-scale integration that would produce a genuinely mixed population.

[00:07:05]What it may indicate is a relationship between modern humans and Neanderthalss that was genuinely varied, sometimes hostile, sometimes peaceful, sometimes something in between across thousands of years of overlapping geographic range.

[00:07:20]The picture that emerges is less of a simple invasion and more of a complex extended contact period whose specific dynamics differed by time and place and circumstance. Now, let's talk about the other mechanisms that have been proposed for Neanderthal disappearance because direct violence is only one part of a multifactor story. Disease is the mechanism that receives the least popular attention and may have been the most significant.

[00:07:46]Modern humans arriving from Africa carried pathogens to which they had been exposed for thousands of years and to which they had through the harsh process of selection developed some degree of resistance. Neanderthalss isolated from these pathogen environments would have had no such resistance. The epidemiological dynamics of a disease naive population encountering novel pathogens are not subtle. The history of European contact with indigenous populations in the Americas who experience catastrophic mortality from diseases that their visitors had adapted to over millennia provides a documented historical analog. A modern human arriving in Neanderthal territory didn't have to be carrying a weapon to be carrying death. The viruses and bacteria they harbored were potentially far more effective at population elimination than any direct violence could be. And unlike violence, disease leaves essentially no recognizable trace in the fossil record.

[00:08:44]The Neanderthal, who died of an introduced respiratory infection 3 months after contact with a modern human group, left bones that look no different from those of a Neanderthal who died of old age. Climate change is another factor that cannot be dismissed. The period of Neanderthal disappearance roughly 40,000 to 28,000 years ago was also a period of significant climate instability in Europe. The Neanderthal population was already under environmental stress before modern humans arrived in numbers. And a stressed declining population is more vulnerable to the additional pressures that a competing species brings than a stable healthy one. Competition for resources is the mechanism that operates without requiring any direct hostile intent. Two species occupying similar ecological niches using similar resources in the same geographic areas are in competition regardless of whether either species understands or intends that competition. By the way, if you want to go even deeper into the secret lives of ancient humans, I just launched a full course called The Secret Lives of Ancient Humans. 10 modules, three plus hours of content covering everything we never talk about on YouTube, what they feared, how they communicated, what hunted them, and much more. Plus, an exclusive PDF guide included. Link in the description. See you inside. Modern humans and Neanderthalss both hunted large game. Both occupied caves and shelters. Both needed the same resources in the same landscapes.

[00:10:17]Modern humans appear to have had certain competitive advantages. Their social networks were larger and longer range.

[00:10:24]The evidence of long-distance trade in materials like shells and pigments in modern human sites indicates connections across much larger geographic areas than Neanderthal social networks appear to have encompassed. Larger social networks provide information advantages. knowing where resources are across a wider area and resilience advantages, being able to call on support from distant allies in lean times. Modern humans also appear to have had more sophisticated projectile technology, spear throwers, and eventually bows and arrows allowed hunting at greater distances and with less physical risk than the close-range hunting techniques that Neanderthal anatomy appears optimized for. If modern humans were more efficient hunters, they could maintain population density in landscapes where Neanderthal populations couldn't, driving Neanderthalss into increasingly marginal territories until those populations were too small and fragmented to maintain viability.

[00:11:20]This is competitive exclusion, the ecological principle that two species competing for the same niche cannot stably coexist and one will eventually eliminate the other through attrition rather than direct conflict. The modern human didn't need to kill the Neanderthal. The modern human just needed to be slightly better at getting food in the same landscape consistently over thousands of years. The mathematics of population dynamics do the rest. Now, let's talk about the Dennisovvens because they are the most mysterious of the extinct human species and the one whose story has been most dramatically rewritten by recent genetic research.

[00:11:59]The Dennisovvens were discovered not from a skeleton but from a finger bone and a tooth found in Denisova cave in Siberia in the early 2000s. The DNA extracted from these fragments revealed a distinct hominin lineage related to but separate from both modern humans and Neanderthalss that had been unknown to science. Everything known about the Denisovvens comes primarily from their DNA and its traces in the genomes of modern humans because the physical fossil evidence is almost non-existent.

[00:12:31]Denisovven DNA appears in modern human populations across Asia and Oceanania with the highest concentrations found in Aboriginal Australians, Papua New Guineians, and some island Southeast Asian populations. Patterns of Denisovven genetic inheritance suggest that modern humans and Denisovvens interbred in multiple locations across Asia over an extended period. Some of the Denisovan genetic variants that persist in modern populations appear to have been beneficial. A gene variant associated with adaptation to high altitude found in Tibetan populations appears to have Denisovven origin suggesting that introgression of Denisovven genes into modern human populations provided adaptive advantages in specific environments. The Denisovvens also appear to have interbred with Neanderthalss. The Dennisova cave fingerbone contained DNA showing Neanderthal ancestry indicating that these two extinct lineages were themselves in contact and produced offspring at some point in their history. The pattern of hominin interaction that emerges from the genetics is not a simple tree of separated lineages but a complex web of contacts interactions and gene flows across multiple species over hundreds of thousands of years. The question of what happened to the Denisovans, whether modern humans were involved in their disappearance through violence or competition or disease, is even harder to answer than the Neanderthal question because we have so little fossil evidence to work with. Their geographic range was apparently vast, potentially covering much of Asia and extending into island Southeast Asia. But the details of their ecology, their lifestyle, and their interaction with modern humans remain largely unknown. What we can say is that the Denisovvens left us something valuable. The genetic legacy they contributed to modern human populations in Asia and Oceanania includes functional variants that helped those populations adapt to specific environments. They are gone, but they are not entirely absent. The adaptation to high altitude that allows Tibetan peoples to live and work at elevations that would incapacitate most lowland humans carries Dennisovven DNA. Every time someone runs a marathon in the thin air of a high mountain, they are in a small but real sense running partly on Dennisovven biology. Let's talk about homo floresensis the hobbit because this case is different from the neanderthal and denisovven stories in important ways and illustrates the variety of mechanisms that may have been operating in different contexts. Homo floresensis survived on the island of Flores in Indonesia until approximately 50,000 years ago when the fossil record goes silent. Modern humans reached the region around this time. The correlation exists here too. But the specific dynamics of island environments are different from continental dynamics. Island populations are smaller, more isolated, more vulnerable to both introduced disease and direct competition for the limited resources of an island ecosystem.

[00:15:45]Whatever happened to homo floresensis on Flores may have happened faster and more completely than what happened to Neanderthalss across a continent. There is also the possibility that homo floresensis was already declining before modern humans arrived for environmental reasons unrelated to human contact.

[00:16:04]Volcanic activity was a feature of Flores's geological history. And a sufficiently large eruption could have severely reduced or eliminated a small island population independently of anything modern humans did. The honest answer for homoplloresensis as for all the extinct hominins is that we don't know with confidence what happened. The timing implicates modern human arrival. The specific mechanism is unknown. The evidence is insufficient to distinguish between the possibilities.

[00:16:34]What we can say is that a species that survived for hundreds of thousands of years on a small island disappeared shortly after modern humans appeared in the region and that this pattern has been repeated enough times in enough places to constitute a pattern rather than a coincidence.

[00:16:50]Now let's talk about something that very rarely gets discussed in popular accounts of hominin extinction but that the genetics has made impossible to ignore.

[00:16:59]the question of what the interbreeding events between modern humans and other hominins actually looked like on the ground and what they imply about the social reality of these encounters.

[00:17:09]Interbreeding between modern humans and Neanderthalss produced offspring. Those offspring survived and reproduced. This means that at some point somewhere a modern human and a Neanderthal produced a child that was raised in a social group. either a modern human group, a Neanderthal group, or some mixed arrangement. And that child grew up, found mates, and passed their genes forward. What that encounter looked like, whether it was consensual, whether it was violent, whether it was the product of long coexistence between neighboring groups or a brief contact between strangers, we cannot know from the genetic evidence alone. The genes record the fact of reproduction. They record nothing about its circumstances.

[00:17:54]But the social implications are real and rarely discussed. A mixed ancestry individual living in a group of either modern humans or Neanderthalss would have been visibly different from group members of the other lineage. How those differences were interpreted. Whether mixed individuals were accepted, rejected or occupied some intermediate social position is entirely unknown. The archaeology doesn't give us access to the social lives of individuals. It gives us objects and bones and those objects and bones are largely silent on questions of social inclusion and exclusion. What we can say is that the genes got through. Whatever the social circumstances, the offspring survived.

[00:18:38]The lineage continued and the Neanderthal contribution to modern human biology, small as it is in percentage terms, includes variants that appear to have been actively beneficial, varants affecting immune function, metabolism, and adaptation to specific environments.

[00:18:55]Modern humans absorbed something useful from Neanderthalss in the process of replacing them. The extinction was not clean. Now, let's return to the central question and try to give the most honest answer the evidence allows. Did modern humans kill the other human species? The most accurate answer is probably yes, in some ways, in some places, and at some times, but probably not only through direct violence, and probably not through anything we would recognize as deliberate, organized extermination.

[00:19:26]What appears to have happened is something more diffuse, more varied, and in some ways more disturbing precisely because of its diffuseness. Modern humans carried diseases to which other hominins had no resistance. Modern humans competed for resources more effectively through better technology and larger social networks. Modern humans interbred with Neanderthalss and denisven leaving their genetic traces in us. But without enough sustained integration to prevent those lineages from declining to the point of extinction and in some specific encounters in some specific places, modern humans may have killed other hominins directly. The result across thousands of years and across the geographic range of every other hominin species on the planet was the same. They disappeared. We remained. There is a version of this story that is comforting. A story in which the disappearance of the other hominins was the inevitable result of natural competition. No different from the replacement of one animal species by a more successful competitor and no more morally weighted than the evolution of any other dominant species. There is a version that is deeply uncomfortable. A version in which our species from its earliest global expansion was defined by a capacity for outco competing, displacing, and occasionally destroying other beings who were by any reasonable measure people like us. Beings who made tools, who cared for their sick, who buried their dead and possibly decorated their bodies and possibly made music and possibly looked at the same stars we look at and wondered about the same things we wonder about. The evidence doesn't cleanly support either framing.

[00:21:04]It supports a messy, complicated, contextually variable story in which modern humans and other hominins coexisted for thousands of years in some regions, interbred, competed, and ultimately produced an outcome in which only one lineage survived with its identity intact. The others were absorbed marginally or disappeared entirely.

[00:21:26]That lineage is reading these words right now. The question of whether to feel implicated in what happened to the Neanderthalss, the Dennisovvens and the others is ultimately a philosophical one rather than a scientific one. The science can tell you what probably happened. It cannot tell you how to feel about it. What it can tell you is that the world we live in, a world with one human species, a world where being human means only one thing biologically, is not the only world that could have existed. For most of the last half million years, it wasn't the world that did exist. There were other kinds of minds, other kinds of human experience, other ways of being the kind of creature that makes tools and buries its dead and cares for its injured. Those ways are gone. The minds that held them are gone.

[00:22:16]the specific experiences of Neanderthal life, what it felt like to be that body in those landscapes with those social bonds, looking out at a world that no longer exists in any form recognizable to us are irretrievably gone. No amount of genetic analysis, no amount of fossil study, no amount of computational reconstruction will give us access to what was lost. The Neanderthal sitting by a fire in a cave in what is now France, caring for an injured companion, was doing something recognizably human.

[00:22:48]The lineage that fire belongs to is gone. The lineage that watched it from across a valley is still here. We carry a small piece of them in our DNA. It is the only monument they have. And the question of whether we deserve to carry it, whether the beings who contributed it to us would consider that a legacy or an insult is one that the science cannot answer and that we are perhaps not equipped to answer honestly. The other humans are gone. We are here. The relationship between those two facts is the most uncomfortable question in the entire history of our species.