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:
Upvote/downvote each of the videos below!
As you vote, keep in mind that we are looking for a winner with the most engaging social venture pitch - an idea you would want to invest in.
Having these financial life skills can help you navigate challenging economic environments.
- Americans are swimming in increasingly higher amounts of debt, even the upper middle class.
- For many, this burden can be alleviated by becoming familiar with some straightforward financial concepts.
- Here's some essential financial life skills needed to ensure your economic wellbeing.
An innovation may lead to lifelike evolving machines.
- Scientists at Cornell University devise a material with 3 key traits of life.
- The goal for the researchers is not to create life but lifelike machines.
- The researchers were able to program metabolism into the material's DNA.
Experts argue the jaws of an ancient European ape reveal a key human ancestor.
- The jaw bones of an 8-million-year-old ape were discovered at Nikiti, Greece, in the '90s.
- Researchers speculate it could be a previously unknown species and one of humanity's earliest evolutionary ancestors.
- These fossils may change how we view the evolution of our species.
Homo sapiens have been on earth for 200,000 years — give or take a few ten-thousand-year stretches. Much of that time is shrouded in the fog of prehistory. What we do know has been pieced together by deciphering the fossil record through the principles of evolutionary theory. Yet new discoveries contain the potential to refashion that knowledge and lead scientists to new, previously unconsidered conclusions.
A set of 8-million-year-old teeth may have done just that. Researchers recently inspected the upper and lower jaw of an ancient European ape. Their conclusions suggest that humanity's forebearers may have arisen in Europe before migrating to Africa, potentially upending a scientific consensus that has stood since Darwin's day.
Rethinking humanity's origin story
The frontispiece of Thomas Huxley's Evidence as to Man's Place in Nature (1863) sketched by natural history artist Benjamin Waterhouse Hawkins. (Photo: Wikimedia Commons)
As reported in New Scientist, the 8- to 9-million-year-old hominin jaw bones were found at Nikiti, northern Greece, in the '90s. Scientists originally pegged the chompers as belonging to a member of Ouranopithecus, an genus of extinct Eurasian ape.
David Begun, an anthropologist at the University of Toronto, and his team recently reexamined the jaw bones. They argue that the original identification was incorrect. Based on the fossil's hominin-like canines and premolar roots, they identify that the ape belongs to a previously unknown proto-hominin.
The researchers hypothesize that these proto-hominins were the evolutionary ancestors of another European great ape Graecopithecus, which the same team tentatively identified as an early hominin in 2017. Graecopithecus lived in south-east Europe 7.2 million years ago. If the premise is correct, these hominins would have migrated to Africa 7 million years ago, after undergoing much of their evolutionary development in Europe.
Begun points out that south-east Europe was once occupied by the ancestors of animals like the giraffe and rhino, too. "It's widely agreed that this was the found fauna of most of what we see in Africa today," he told New Scientists. "If the antelopes and giraffes could get into Africa 7 million years ago, why not the apes?"
He recently outlined this idea at a conference of the American Association of Physical Anthropologists.
It's worth noting that Begun has made similar hypotheses before. Writing for the Journal of Human Evolution in 2002, Begun and Elmar Heizmann of the Natural history Museum of Stuttgart discussed a great ape fossil found in Germany that they argued could be the ancestor (broadly speaking) of all living great apes and humans.
"Found in Germany 20 years ago, this specimen is about 16.5 million years old, some 1.5 million years older than similar species from East Africa," Begun said in a statement then. "It suggests that the great ape and human lineage first appeared in Eurasia and not Africa."
Migrating out of Africa
In the Descent of Man, Charles Darwin proposed that hominins descended out of Africa. Considering the relatively few fossils available at the time, it is a testament to Darwin's astuteness that his hypothesis remains the leading theory.
Since Darwin's time, we have unearthed many more fossils and discovered new evidence in genetics. As such, our African-origin story has undergone many updates and revisions since 1871. Today, it has splintered into two theories: the "out of Africa" theory and the "multi-regional" theory.
The out of Africa theory suggests that the cradle of all humanity was Africa. Homo sapiens evolved exclusively and recently on that continent. At some point in prehistory, our ancestors migrated from Africa to Eurasia and replaced other subspecies of the genus Homo, such as Neanderthals. This is the dominant theory among scientists, and current evidence seems to support it best — though, say that in some circles and be prepared for a late-night debate that goes well past last call.
The multi-regional theory suggests that humans evolved in parallel across various regions. According to this model, the hominins Homo erectus left Africa to settle across Eurasia and (maybe) Australia. These disparate populations eventually evolved into modern humans thanks to a helping dollop of gene flow.
Of course, there are the broad strokes of very nuanced models, and we're leaving a lot of discussion out. There is, for example, a debate as to whether African Homo erectus fossils should be considered alongside Asian ones or should be labeled as a different subspecies, Homo ergaster.
Proponents of the out-of-Africa model aren't sure whether non-African humans descended from a single migration out of Africa or at least two major waves of migration followed by a lot of interbreeding.
Did we head east or south of Eden?
Not all anthropologists agree with Begun and his team's conclusions. As noted by New Scientist, it is possible that the Nikiti ape is not related to hominins at all. It may have evolved similar features independently, developing teeth to eat similar foods or chew in a similar manner as early hominins.
Ultimately, Nikiti ape alone doesn't offer enough evidence to upend the out of Africa model, which is supported by a more robust fossil record and DNA evidence. But additional evidence may be uncovered to lend further credence to Begun's hypothesis or lead us to yet unconsidered ideas about humanity's evolution.
SMARTER FASTER trademarks owned by The Big Think, Inc. All rights reserved.