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The mystery of the Neolithic bottleneck may be over, thanks to one plucky undergrad
At one point during the Neolithic era, the Y-chromosome in our species became far less diverse. Called the Neolithic bottleneck, the reason for it may have finally been revealed.
The Neolithic period or “New Stone Age,” developed at different times in different regions, but is generally thought to have taken place between 7,000-9,000 years ago. An important era in human development, this time period is best known for the Neolithic revolution. Here, humans began to take part in large-scale agriculture, domesticating large herds of animals, building megalithic architecture, and using polished stone tools.
Then, starting around 7,000 years ago and taking place over the next two millennia, something odd happened. The diversity of the Y-chromosome plummeted. This took place across the continents of Africa, Asia, and Europe. It’s the major reason why humans are 99.9% identical in genetic makeup today. The Neolithic Y-chromosome bottleneck (as it’s called) has stymied anthropologists and biologists since it was first discovered in 2015. Now, the mystery may have been solved.
Declines in genetic diversity in a given human population aren’t unheard of. Oftentimes, a natural disaster will wipe out a large segment of a society. During the Neolithic bottleneck, curiously, only men were affected. While experts have been contemplating the bottleneck for years, this hypothesis was made by undergraduate and sociology major, Tian Chen Zeng.
Zeng scoured blog posts and over time, developed his own theory. In many societies at the time, power was organized around patrilineal kinship. A patrilineal lineage is when titles, lands, and the family name are handed down through the males of a family, from one generation to the next. Zeng surmised that intense warfare between patrilineal clans killed off so many men, only one was left for every 17 women. As a result, just a few lineages saw rapid expansion.
Skara Brae. A Neolithic stone settlement. It's located on the Bay of Skaill, on the largest island in the Orkney archipelago, off the coast of Scotland. Image credit: Dr. John F. Burka, Wikipedia Commons.
Zeng decided to employ the help of another Stanford undergraduate, Alan Aw. A high school friend of Zeng’s, Aw was now studying mathematical and computational science. The two approached Stanford biology professor Marcus Feldman. Once Feldman was onboard, the trio began to unravel the mystery. Their conclusions were published in the journal Nature Communications.
While women married into clans in a patrilineal society, all the men within one were related, and therefore carried the same Y-chromosome. Ergo, over the course of long-term, brutal warfare, many clans were wiped out and with them, their particular type of Y-chromosome. This took place over the course of 2,000 years. It’s important to note that there’s a difference between population and genetic diversity. While there could have been the same number of men or more than before, they were mostly from the same few clans, and so carried the same Y-chromosome.
Those clans successful in warfare grew wealthy and powerful. As such, the monarch and his sons had exclusive mating rights. They could have many wives, concubines, and/or courtesans each, and so the genetic diversity of our species dwindled. Using mathematical models and computer simulations, researchers showed that Zeng’s hypothesis is indeed possible. Their findings also corresponded with ancient European DNA samples.
Interestingly, conflict among non-patrilineal clans did not reduce the diversity in the Y-chromosome. This is where both men and women can move from one clan to another, usually changing clans due to marriage. The Y-chromosome bottleneck varied depending on location. It was more pronounced in Europe, the Near East, and South Asia, and less so in East and Southeast Asia. The most useful result wasn’t the findings themselves, but the method which was applied. Weaving together mathematics, biology, and sociology in such a way was so dynamic, researchers are now considering plying it to other such quandaries.
According to the report, another place this method could be applied is, "An investigation into the patterns of uniparental variation among…the Betsileo highlanders of Madagascar, who may have undergone an entry and an exit from the 'bottleneck period' very recently.” This “could reveal phenomena relevant to such history." Organizational and political changes may have altered the human genome in other ways too, which perhaps this method could, in time, reveal.
To learn about a more modern crisis surrounding the Y-chromosome, click here:
Sallie Krawcheck and Bob Kulhan will be talking money, jobs, and how the pandemic will disproportionally affect women's finances.
When facing a tough decision, it pays to trust your gut.
- A recent study examined the accuracy of predictions of soccer matches on a popular betting website.
- The users were allowed to revise their bets up until the match started.
- Surprisingly, the results revealed that the revised bets were much more likely to be incorrect.
Why did users change their minds?<p>"We can only speculate, but we might imagine that game players input their initial forecast, following which they look at the latest online betting odds on the match, or look for other information which might affect their judgement, such as news on team selection for the match," the researchers wrote. "Alternatively, these revisions could simply be the result of changes to initial judgements without any new information."</p><p>You might think the ability to revise your prediction would be an advantage. After all, maybe you had more time to carefully consider which team is more likely to win. Maybe public opinion on the two teams had shifted over time. Or maybe one of the teams had recently begun an incredible winning streak.</p><p>But the results of the study showed that prediction accuracy decreased significantly — by about 17 percent — when users revised their original predictions. Why? Given that the study controlled for variations by players and teams, it's unlikely that the drop-off in accuracy was due to some matches being harder to predict than others, or some users being better predictors than others.</p>
Pixabay<p>One possible explanation is a behavioral bias that describes how people are likely to overreact to news that is salient. So, when you learn, for instance, that a player on one of the teams was injured, you might respond excessively to that news, leading you to revise your original prediction.</p><p>The results revealed that revisions made after a longer period of time, as opposed to just a few minutes, were much less likely to be correct. Also, users were less likely to predict correctly when their revised predictions included <em>higher scores</em>, for example, changing a 1-2 outcome to a 2-3 outcome. Interestingly, most users underestimated the likelihood of a 0-0 draw. Broadly, this suggests that we tend to falsely believe it's more likely for <em>something to happen </em>than <em>nothing.</em></p>
Trust your gut<p>The researchers wrote that their findings "could have relevance to other contexts where judgmental forecasting explicitly takes place and which have real economic importance, such as in company management and planning, financial markets and macroeconomic policy."</p><p>Of course, sometimes new information <em>should </em>cause us to revise our decisions. But for situations where new information is unlikely to significantly alter the outcome, the results suggest it's best to make a decision and stick with it.</p><p>This aligns with research from Stanford professor Baba Shiv, an expert in the neuroscience of decision-making. Shiv's research found that, even though we often face tough trade-offs when making complex and emotional decisions, a key component of successful decisions is staying committed to our choice. Shiv <a href="https://hbr.org/2013/11/stop-worrying-about-making-the-right-decision" target="_blank">told</a> Stanford Business magazine: "When you feel a trade-off conflict, it just behooves you to focus on your gut."</p>
The coronavirus pandemic has brought out the perception of selfishness among many.
- Selfish behavior has been analyzed by philosophers and psychologists for centuries.
- New research shows people may be wired for altruistic behavior and get more benefits from it.
- Crisis times tend to increase self-centered acts.
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