Recently [read: many busy months ago…] I finished reading “The Invaders”, an interesting little book in which Pat Shipman discusses her theory that, around 35,000 years ago modern humans entered Europe, began domesticating dogs, and, acting as an invasive team, the two reshaped the ecosystem. Former top predators such as cave lions, lesser scimitar cats, and neanderthals were driven to extinction.
As soon as this book came onto my radar I pre-ordered it, and I devoured it as soon as it arrived. I’m endlessly fascinated by early human history, and the Invaders did not disappoint.
Unlike Across Atlantic Ice, which read, in parts, like 20 academic papers binder-clipped together, I found The Invaders to be a very pleasant read (though it was by no means short on references).
As Pat herself mentions, it’s tricky to write on the topic at the moment – new lines of evidence are being uncovered at such an astounding pace that anyone committing ideas to print risks looking foolish two months down the road.
I have been wanting to explore the topic of the neanderthal -> sapiens transition for some time. One fully formed idea has been on my todo list since at least last January. I’ve hesitated to post anything on the topic before the video I had planned was ready, but, as I wrote earlier, bets need to be made while the wheel is still spinning.
Therefore, using “The Invaders” as a stepping off point, I’m going to tip my hand a bit about some of my own pet theories.
I have to say, I was somewhat shocked that viewing humans as an invasive species could be presented as a new idea. To me it seems obvious. However, even if the idea is self-evident, what may be new is the use of analytical models developed to study how invasive species spread.
From the perspective afforded by these models, the total displacement of neanderthals and other dominant predators in Europe by modern humans is completely unsurprising.
Most new species entering into a novel environment do not succeed. Those few that do, however, tend to do spectacularly well. Furthermore, it is very rare for a 50/50 equilibrium to develop between two species vying for the same niche. Either they will find a way to subdivide the niche, or one species will almost inevitably be eliminated.
Predators tend to speed this process along by preferentially targeting their closest competitors. Thus, as Europeans entered the West, they targeted first the indigenous people, and then the wolves, doing all they could to wipe out the competition.
Likewise, when wolves were re-introduced to Yellowstone, they preferentially targeted coyotes, who were close competitors for their niche. The closest competitors though, are other wolf packs, and wolves are indeed most vicious with interloping wolves from other groups who dare to approach their kills.
In 2004, despite the trumpeting of mtDNA evidence suggesting that humans and neanderthals had never mated, I remained skeptical, because interbreeding is apparently very common between closely related groups of apes whose territories overlap. Turns out, this pattern held within the genus Homo.
However, the fact that the two species interbred at times certainly does not suggest a love fest.
To the extent that modern humans did interact with Neanderthals, I think it’s reasonable to expect that most of the encounters included aggressive posturing and intimidation, if not ambushes and death.
To the extent that their niches differed, sapiens preferring open grasslands for pursuit, while neanderthals preferred forests for ambush hunting, there may have been a few thousand years of uneasy equilibrium.
After a few encounters with these terrifying new competitors, neanderthals may have shrunk back, ceding the grasslands. However, to the extent that they did hang on, I think it’s reasonable to expect that neanderthals would have defended their refuges with ferocity and cunning.
While perhaps superior predators, modern humans might have developed a healthy fear of these environments and largely avoided them, just as they might a lion’s den. Perhaps we see echoes of this respect passed down through oral histories. (Isn’t it interesting how trolls always seem to be ambushing people at stream crossings in the woods?)
I’ve come across a number of articles recently where people talk about a “Lord of the Rings” world, with multiple varieties of human inhabiting the same continent. This is a convenient, easily comprehensible shorthand, but I think it’s an idea that deserves actual scholarship. Remember that Tolkien was an avid reader of early legends and many of these elements he admired flow directly into his works. Should we be at all surprised then, to find echoes of the upper paleolithic in Middle Earth?
But I’ve digressed. The idea at the core of Shipman’s book is that, shortly after entering Europe, a group of modern humans domesticated wolf-dogs, and it was this newly formed alliance between two top predators which allowed them to drive the remainder of their competitors to extinction.
I think it’s a fascinating idea, and I find the evidence Shipman presents for this early wolf domestication in Europe convincing. Certainly having a pack of braying wolf-dogs could have made it much easier for modern humans to corner large prey and then defend the carcasses indefinitely, which they had never before been able to do. However, as Shipman herself admits, no evidence yet exists to suggest that an early human-“wolf-dog” alliance played a significant role in the extinction of the neanderthals.
While dogs may have been domesticated as early as 32,000 years ago, neanderthals, if any still existed at that point, were likely to be in irrevocable decline, their low density and long gestation period having made them them especially vulnerable to new competitors, with or without dogs.
In fact, Bjorn Kurten’s hypothesis in Dance of the Tiger is beginning to sound better and better. New evidence apparently suggests that the male neanderthal/human crosses might have been infertile. Even if humans and neanderthals had consensual sex as often as they killed each other, given that humans lived more densely on the land than neanderthals, we should expect the descendants of a population of occasionally interbreeding groups to look mostly sapiens-sapiens in the end. (I’ve been planning to do a video roughing out some of the crude mathematical differences between humans and neanderthals, but don’t hold your breath…)
Speaking of prescient authors, as much as I have (and will continue to) poke some fun at “the girl who invented everything” series, it appears that Auel’s scenario for dog domestication (aren’t these pups adorable!) may be more likely than the scenario of wolves scavenging from garbage dumps. Given that wolves who become accustomed to humans around garbage dumps actually become more aggressive, Shipman believes that dogs would have had to have been domesticated from pups.
In my mind, the primary development which allowed modern humans to displace neanderthals was domestication – not of dogs, but of themselves.
As I see it, somewhere in Africa there was a population of humans living in a resource-rich, possibly marine environment, where, because of the relative poverty of surrounding environments, there was a benefit to staying put, rather than finding a new territory. Thus those populations who evolved the capacity to live in denser groups were more reproductively successful in that area.
Though the end result was a more harmonious group, the mechanism was likely targeted killings of the more aggressive males. (Though banishment from the breeding population might have been sufficient).
Domestication in mammals appears to be in some way correlated to the movement of neural crest cells in the developing embryo. In the cases where these cells do not complete the full journey observed in wild individuals, certain developmental patterns emerge: floppy ears, changes in coloration, smaller teeth, and more agreeable disposition. Domesticated pups are more likely to become attached to human caretakers, but domesticated hominids are perhaps also more likely to find the pups endearing rather than appetizing. Perhaps our own auto-domestication pre-disposed us to further domestication.
As these early humans became more agreeable, they also became more altruistic. In “Wired for Culture” Mark Pagel discussed how a “greenbeard” gene could be selected for across individuals. Natural selection allows for the development of a gene which encourages all individuals who share the gene to cooperate with each other. The stumbling block in the development of such a gene is the difficulty (from the gene’s perspective) in determining which individuals have the gene and “warrant” cooperation, and which are faking it.
Pagel elegantly explains how altruism itself might be thought of as a greenbeard gene. In signaling theory, the costlier the signal the more reliable it is, and selfless altruism itself is costly. Thus by performing acts of selfless altruism, an individual signals to those around her that she shares the altruist genes and is a deserving subject of their altruism. So long as altruism is bestowed mostly on other altruists, this adds up, even by the coldest rational accounting.
It is interesting to note that the neanderthal brain was on average 14% larger than that of modern humans. This lines up with other cases of domestication: the aurochs had a larger brain than modern cattle, and wolves have larger brains than dogs (and score more highly on most measures of intelligence). Some argue that while they had bigger brains they weren’t smarter, just better at moving and seeing in the dark, but to me this argument smells of phrenology.
I think it’s likely that, if you could have devised a fair test, an individual neanderthal might have proved more intelligent than a modern human.
The aurochs may have been wilier, but it was less inclined than its cousin, the domesticated cow, to live with humans. The last aurochs died in 1627 while the cow is still going strong. It was not individual humans who displaced neanderthals but human cultures.
Perhaps we can think of insights and innovations as mental events which might be increased by necessity and raw intelligence, but are also distributed somewhat randomly. It’s a numbers game. Over the course of a year, I think it’s reasonable to assume that a group of 20 individuals of mediocre intelligence might come up with a few more valuable insights than a group of 5 smart individuals.
Once a group develops a reliable way to hang on to the best of these insights, it has a significant advantage over competing groups, especially if it can guard access to the information (and to the fruits of altruism) from would-be interlopers. (Say by encoding it in a different language…)
Apparently, having a significant number of individuals live into old age is a development of the upper paleolithic. My suggestion is that, once population density increased and cultural innovations began to multiply, the advantage of retaining older group members increased. Grandmothers were the original libraries.
This is the nature of human cultures – warm and squishy for insiders, but wary and suspicious towards outsiders. It’s interesting to note that oxytocin facilitates the bonding between mother and child, but also makes people more suspicious of outsiders.
Evolution is a competitive process. While there may be an advantage to acting altruistically towards individuals who are not your close relatives, (and in the context of a stable society it can make perfect sense to act as a selfless altruist without discrimination) there is a selective benefit to drawing the line somewhere.
In “Wired for Culture” Mark Pagel suggests that as groups reach a certain size, individuals feel driven to differentiate their subgroup from other subgroups. In this model, languages and customs diverge not because of prolonged isolation, but from overcrowding and social confusion. Thus we see the greatest density of differentiated languages not in the sparse arctic, but in Papua New Guinea. “There are regions of the northeast corner of coastal Papua New Guinea where a different language is spoken every few miles.” (Wired for Culture, p ix)
I like to imagine cultures as cells which divide. Individuals are like the organelles and structures of a cell. Young men play the role of the cell wall, protecting the interior and perhaps occasionally engulfing other, weaker cells. The elders are like the nucleus of the cell, storing the cultural information and slowly passing it down. Young women are perhaps the mitochondria. (While animal foods might intermittently provide protein, fat, and crucial nutrients, women typically gather most of the day-to-day calories.)
Once a culture grows to a certain size it begins to develop sub-cultures, and once a sub-culture reaches the point of self-sufficiency, it splits off the original culture like a daughter cell.
When picturing the human colonization spreading out of Africa, you can visualize it on one level as a flow of humans, or you can picture it as a series of cultures each budding new cultures, occasionally consuming each other, and spreading across the landscape, adapting to new niches as they encounter them.
This modern human method of culture adaptation is much faster than genetic adaptation, so once modern humans developed enough cultural adaptive capacity to thrive in the former neanderthal niche, the actual displacement probably occurred very quickly.
Thus the ability to get along with our neighbors spelled the end of our closest relatives.