Here's the original article that caused such a stir in 2015. Figure 2 shows the sudden drop in the reproducing Y-population globally (meaning it cannot be explained by genes or migration).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381518/
The paper cited in the article alters the date of the event, but really there's a lot of uncertainty remaining.
https://www.nature.com/articles/s41467-018-04375-6
The best current hypothesis to explain this drop (and that no similar one occurred for the reproducing X-population) is the conflict between predominantly agricultural societies versus predominantly hunter-gatherer societies. Until sufficient evidence has been found to rule out this or alternatives, take any explanation with a grain of salt.
Look at Figure 2, and you'll notice the Y-axis are different. Between 50-10kya, the effective reproductive population was 3-4 times larger for women than men, globally. This fits with modern anthropological evidence of polygyny in early hunter-gatherer cultures (loose polygyny with on average 3-4 wives per successful male over a lifetime, but with limited ability to enforce fidelity). Y chromosome diversity tends to accumulate, albeit at a lower rate than the X.
An agricultural community is likely to be much more homogenous in terms of Y-chromosomes, than a hunter-gatherer one. Power is much more effectively concentrated in these communities, allowing leaders to amass more wives and enforce fidelity much more strictly than in hunter-gatherer societies. Stories of King Solomon's wives, or Sultan Moulay Ismail of Morocco (who reportedly sired hundreds of children) are an easy way to visualize this.
While man-for-man, a hunter-gatherer may be healthier and stronger, a hunter-gatherer society may find themselves vastly outnumbered by an agricultural community. Over time, hunter-gatherers would find themselves pushed off of prime land onto marginal land. The newer article mentions a founder effect. Where are these Neolithic pioneers coming from and where are they going to? From agricultural communities, expanding into territory previously held by hunter-gatherers. While certainly many deaths occurred due to combat, Y-chromosomal diversity loss also would have occurred to disease and famine. The agricultural population would continue to rise, while the hunter-gatherers would struggle to maintain on more marginal land. History is replete with stories of taking women, so if this scenario is the best explanation, it is unsurprising that there was not a corresponding drop in X-diversity.
This sort of scenario occurred globally. Agriculture independently arose in many places: the near-east, sub-saharan Africa, China, Mexico, the Andes, and possibly others. We've seen what happened to the Americas after Columbus. Similar mechanisms help explain the population-level Y-cide on smaller scales that probably occurred during each of the agricultural expansions above.
This hypothesis, while probably the most widely-accepted at present, is challenged by some of the evidence in the newer paper. It will be interesting to see how it falls out once the original authors have a chance to respond or additional voices join the conversation.
1. How, in layman's terms, are they reconstructing the history of the genomes from current genome samples? (I think that's what the paper you mention says, but I'm not sure.)
2. My understanding is that the creation of agriculture was separated by thousands of years between the centers (near East, China, etc.), followed by thousands of years spreading from each center. The figure in your first paper makes the bottleneck appear essentially simultaneous world-wide. What's up with that?
2. I'm very interested to know the answer to your second point myself. As displayed in figure 2, it looks like it wasn't exactly simultaneous or equal in magnitude everywhere. It does look like most geographic clusters did see something of a drop, at some point. Eyeballing it, it appears that the near-East and the Caucasus had the relatively most-significant drop. The African cluster appears to have had a more modest drop and at a later date. However, I wouldn't rely too heavily on trying to read more into the figures than the authors did (and as I just tried to do).
I suspect the resolving power their data sample gave them was insufficient to resolve your question. While it was enough to demonstrate the existence of such a drop, I would be skeptical of its power to demonstrate the relative severity or timing between each geographical cluster. (If I was the author, this finding would be begging for more grant money to do exactly that: gather more data and nail down exactly how much, when, and where the Y diversity was lost.)
Final point: it's not necessary to assume everyday life was brutal or violent. I'm not an anthropologist, so take my reference to Napoleon Chagnon with a grain of salt. The Amazonian Yanomamo people he lived among had high rates of violent death compared to other causes of death, yet everyday life was peaceful. Most of the bloodshed and conflict he documented occurred over very few days in quick moments. When a population is low, it doesn't take much to move the % up a lot.
Whatever caused the drop in Y diversity, if it happened over several thousand years, the yearly attrition rate could have been very low also.
Seriously, you might have missed it but people on HN have an astonishing variety of professional backgrounds. On many occasions, I've read the most enlightening comment on some news here on HN.
That said, would it be (semi) safe to presume that the most fittest survived, and those likely being the most (for lack of a better term) ruthless? That is, the gene pool (on the male side) leaned towards violence (as a means of survival). That in turn served as the foundation of white Western Europe repeatedly exerting itself as a superior culture.
And at the extremes, this helps explains serial killers, mass murders, etc. That is, today's violence was yesterday's survival skills. Some of those genes remain in the gene pool. At least in theory, yes?
this replacement (sedentary agriculturalists killing/pushing out hunter-gatherers) happened everywhere in the world, not just 'white western europe'
The collapse of Y chromosome diversity around the transition to agriculture and civilisation is far from being exclusive to white or European culture. It happened in every human population that took up agriculture, to greater and lesser extent.
Violence is absolutely part of human nature. Serial killers are probably pathological but mass murder is definitely within normal human behaviour. The Mongols were less especially brutal than especially organised, ditto for the Nazis at a later date.
Kill everybody and take their land is more or less what happened to both the Neanderthals and the first H. Sapiens in Europe. Kill all the men is practically a humanitarian innovation.
Systematic violence is ultimately very rational. Your worst enemy is always your neighbor or a trespasser. Agriculture requires ownership of land, so hunters are always the enemy of the farmer.
other explanations included, its no surprise that there's a sudden die off of male lineages in the Y with agriculture coming into the scene.
to me, its another example of yin/yang creation/destruction push/pull where males drive evolution through destruction and females preserve the species dna.
https://web.archive.org/web/20170213235609/https://en.wikipe...
(wiki was inexplicably deleted recently, i suspect for political reasons via rules lawyering)
> Geodakyan suggested that sex dimorphism gives a species the benefit of having two functional partitions, or subsystems. The male sex is considered an operative, variation subsystem, while the female sex is a conservative one. Sex differentiation allows a species to use the male partition to try out various genetic changes, including parasitic and cooperative co-existence for possible inter-species co-evolution and expansion of ecological niches. In Geodakyan's terms, species use males as an experimental partition of sex and use another partition (female) to maintain the features of the species that were proven to be beneficial.
Somewhat better: Statement X contradicts Figure 2.
Much better: Statement X contradicts Figure 2 because Y.
Typical hn. Typical.
Assume that humans are living in patrilineal clans of roughly 20 males and an equivalent number of females. All males are genetic descendants of the clan patriarch and share the same Y-chromosome markers. All females are born outside the clan and marry into it.
Now assume that 95% of clans are wiped out through a couple millenia of warfare. That Y-chromosome is now extinct; all male-line descendants of the patriarch are dead. However, genetic markers carried by the female are not extinct, because the 20 daughters born into the clan have married into 20 different clans, and at least one of them has survived.
Note that the population doesn't actually have to drop in this scenario! 95% extinction of clans over 2000 years implies only 0.15% extinction annually, assuming an exponential decay. If warfare is continuous and resources go to the victor, then one clan is exterminated, but the victorious clan quickly doubles in size as it takes the dead clan's resources (and oftentimes, womenfolk). Total population remains roughly constant, but all living descendants come from a tiny percentage of male ancestors.
Other articles about this study have made this distinction explicitly (or at least hinted about it), but it's totally missing from the headline.
There are a very few matrilocal human societies; perhaps they show the obverse pattern.
The neolithic period was one of agriculture and early civilization. Stonehenge was built by neolithic peoples, and Egypt, Mesopotamia and China were embryonic civilizations in the neolithic era as well. Cavemen, these were not.
Maybe the URL for this submission could be changed?
https://en.wikipedia.org/wiki/Cucuteni%E2%80%93Trypillia_cul...
Talianki, 4000 BC.
https://en.wikipedia.org/wiki/Cucuteni%E2%80%93Trypillia_cul...
Maybe the reason civilization is even possible today is that the majority of our potential ancestors who couldn't deal with civilized life wiped each other out. Or alternatively, the males who survived were really good at warfare and surviving warfare.
And yes, societies which are better at warfare tend to also have better agriculture, tools, etc, to support their military machine.
An interesting parallel would be Starcraft AI. It excels at micro, but fails at macro, like tricking the opponent into building the wrong units.
But beyond the warfare stuff, another key selector would have been intelligence. Give two groups of people sticks and stones and I'm betting on the smarter. You don't need much strength to kill with even those weapons, and all the strength in the world isn't going to help you when you get hit. Perhaps it's the case that we still some of this today as it relates to Genghis Khan as the mongoloid group of peoples tend to have some of the highest average visual/spatial IQs on the planet.
Likewise, lower intelligence might reduce personality differences and increased coordination. Individual troops with less foresight may be more careless of their own safety and thus more fierce on the battle field. In the manner of bees. Also, in a warrior society, obedience maybe favored over independent thinking.
Also, in an pre-agricultural societys everyone is a generalist: everyone must be smart enough to know how to do everything. Less true in agricultural societies.
So it's just as possible agriculture made people dumber but more dense population centers and thus more effective militarily.
My point is that barring actual measurement, we can conceive a great many possibilities and at this point no measurements indicate intelligence change over that period
So not so much surviving warfare as much as an increasing capability to control it so it took place away from the productive infrastructure. A pattern we see to this day.
A bit unbelievable, given that the cities get back in business quickly, but population centers have apparently always been centers for conflict.
What kind of World War Zero could possibly explain this? I really can't picture how a state of sustained (for thousands of years?) high-intensity warfare over an area spanning three entire continents could have worked. How many historical instances are there of a population decreasing to 1/20th of previous levels? The 20th century had a couple of instances but that required totalitarianism and modern communication, logistics, and industrial capabilities.
The other historical instance I know of is the decimation of New World populations after contact with Europe (through disease). I don't know what other evidence they've assembled, but disease feels like a much better way to explain this population drop than warfare.
But what diseases only target males? Dunno. Maybe the early domestication of livestock introduced some kind of chickenpox or dogpox that killed (or sterilized!) males dramatically more frequently than females.
Wolbachia is a parasite that, as I understand it, kills male infected at a very young age. Now, this only affects insects, but it does show that something this level of sex-selective is possible.
Imagine tribes filled out over populated Europe like cells. They raid each other, kill men, take women and now that Y chromosome fills 2 cells.
Push an exponentially increasing 1 tribal diameter of area per generation at the front and it doesn't take many generations for almost replacement.
Article 'A SUDDEN and dramatic drop in the number of human males living in Europe, Africa, and Asia 7,000 years ago is evidence of brutal warfare spanning multiple generations, a new study has suggested.'
Theory is fact in click bait tabloid headlines...
a new study has suggested, terminal qualifiers are often ignored
I think we also need to recognize how we got to this point though.
.jpg){kind=link}
.jpg){kind=link}