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Population Bottlenecks?

Nah, just our Albinos trying to explain their homogeneity without acknowledging their Albinism.

Common quote: population bottleneck that is often cited as the reason for

the relatively low genetic diversity across Homo sapiens.




Please note that Black people are depicted above as the effected community:

this is addressed at the end of this page.


This means that, for a while, humanity was in a perilous state, vulnerable to disease, environmental disasters and conflict. If any of these factors had turned against us, we would not be here.

The research also suggests that humans (Homo sapiens sapiens) made their first journey out of Africa as recently as 70,000 years ago. Unlike our close genetic relatives - chimps - all humans have virtually identical DNA. In fact, one group of chimps can have more genetic diversity than all of the six billion humans alive today. It is thought we spilt from a common ancestor with chimps 5-6 million years ago, more than enough time for substantial genetic differences to develop. The absence of those differences suggests to some researchers that the human gene pool was reduced to a small size in the recent past, thereby wiping out genetic variation between current populations.

Evidence for that view is published in the American Journal of Human Genetics. Because all humans have virtually identical DNA, geneticists look for subtle differences between populations. One method involves looking at so-called microsatellites - short, repetitive segments of DNA that differ between populations. These microsatellites have a high mutation, or error, rate as they are passed from generation to generation, making them a useful tool to study when two populations diverged. Researchers from Stanford University, US, and the Russian Academy of Sciences compared 377 microsatellite markers in DNA collected from 52 regions around the world.

Analysis revealed a close genetic kinship between two hunter-gatherer populations in sub-Saharan Africa - the Mbuti pygmies of the Congo Basin and the Khosian bushmen of Botswana. The researchers believe that they are "the oldest branch of modern humans studied here". The data also reveals that the separation between the hunter-gatherer populations and farmers in Africa occurred between 70,000 and 140,000 years ago. Modern man's migration out of Africa would have occurred after this.

An earlier genetic study - involving the Y chromosomes of more than 1,000 men from 21 populations - concluded that the first human migration from Africa may have occurred about 66,000 years ago. The small genetic diversity of modern humans indicates that at some stage during the last 100,000 years, the human population dwindled to a very low level. It was out of this small population, with its consequent limited genetic diversity, that today's humans descended.

Estimates of how small the human population became vary but 2,000 is the figure suggested in the latest research."This estimate does not preclude the presence of other populations of Homo sapiens sapiens (modern man) in Africa, although it suggests that they were probably isolated from each other genetically," they say. The authors of the study believe that contemporary worldwide populations descended from one or very few of these populations. If this is the case, humanity came very close to extinction.



If Hollywood’s right, the apocalypse will be brutal. Aliens, nuclear war, zombies, plague, enslavement by supersmart robots — none of them are good endings. Some archaeologists, however, believe an apocalypse has already come and gone. About 75,000 years ago, they say, a monster volcanic eruption nearly wiped out humankind, leaving behind only a few thousand people to repopulate the world. The explosion of Indonesia’s Toba volcano was the largest eruption of the last 2 million years. The volcano coughed up some 2,000 to 3,000 cubic kilometers of ash, enough to fill almost three-quarters of the Grand Canyon. Unleashing hordes of light-blocking particles, an eruption that size should have cooled the planet and reduced rainfall, killing off plants and creating food shortages. Archaeologists recognized in the late 1990s that the disaster might explain a population bottleneck recorded in modern people’s DNA. Genetic evidence indicates that the human population drastically declined and variation in the gene pool plummeted around the same time Toba exploded.

The story sounds neat and tidy. But researchers are still trying to verify whether our species’ near-extinction experience was fact or fiction. One way scientists have approached the issue is by simulating the climate after Toba’s eruption. In 2009, researchers reported in the Journal of Geophysical Research: Atmospheres that global temperatures could have dropped by 8 to 17 degrees Celsius and taken a few decades to get back to normal. That extended volcanic winter, they noted, would have had “devastating consequences for humanity and global ecosystems.”

The tricky part of these simulations is estimating how much sulfur — the main cause of volcanic climate cooling — Toba expelled. Another problem is incorporating all of the processes that affect the atmospheric life cycle of sulfur particles. Last year, a team attempted to account for these factors and concluded that the consequences of Toba weren’t so dire and varied regionally. In East Africa, for example, temperatures would have fallen only 4.5 degrees C while in India they would have dropped almost 9 degrees C; in both areas, temperatures would have returned to normal within five years, the team reported in Quaternary International. In these simulations, dry grasslands would have replaced forests in many places, but that alone wouldn’t have led to widespread starvation and death.

The geologic record also offers mixed messages. Ice cores from Greenland and Antarctica contain a spike in sulfate concentrations dated to approximately the same time that Toba erupted. Six years of elevated sulfate levels coincide with the onset of a global cool period recorded in the cores. But critics point out that no volcanic ash has been found in the cores to directly link the chill to Toba.

Other geologic clues also suggest the volcano didn’t cause much of a climate calamity. In April, two geologists and an archaeologist announced that they had discovered traces of Toba’s eruption in a sediment core from East Africa’s Lake Malawi. The core contained shards of microscopic volcanic glass with the same chemical composition as glass known to have come from Toba. The core also indicated that temperatures declined by no more than 1.5 degrees C after the eruption, the researchers report in the Proceedings of the National Academy of Sciences. That wouldn’t have had a big ecological impact on East Africa, they say, where a big bulk of the human population presumably lived 75,000 years ago.

Humans elsewhere seem to have survived unscathed as well. In southern India, archaeologists have found collections of stone tools from before and after the eruption that look nearly identical. The tools resemble those made by people living in Africa at the time, circumstantial evidence that Homo sapiens, not some other hominid species, was living in the area pre- and posteruption. But without fossils, which are lacking in India, archaeologists can’t be 100 percent sure that a different Homo species didn’t make the artifacts.

In recent years, geneticists have started questioning their own evidence for a population bottleneck. While some researchers estimate that the decline in the human population happened but preceded Toba by tens of thousands of years, others think people never actually approached extinction. In some situations, cultural behaviors and customs that limit mating between different groups can result in genetic patterns that match those produced by population bottlenecks, anthropologists reported in 2009 in the Proceedings of the National Academy of Sciences.

Finding more climate records that can be directly tied to the Toba eruption and the period when it erupted should help researchers reach more definitive answers. That’s a difficult task given that the timing of the eruption itself isn’t quite nailed down yet, with dates ranging from 73,000 to 75,000 years ago. A precise age is important because the volcano’s actions would have altered climate in a matter of months and years, not centuries and millennia. Unfortunately, even the best scientific stories are never as easily resolved as a Hollywood blockbuster.


It turns out humanity has been almost wiped out a few times in our distant past. How did it happen, and what does it mean for the future of human evolution?

Scientists can spot near-extinctions by correlating several different pieces of evidence. First, by studying DNA samples, counting mutations and measuring genetic diversity (Alu sequences and mitochondrial DNA being especially useful in this regard), they can find population bottlenecks. A bottleneck indicates that for some period of time a given species had very low numbers. This reduces genetic diversity, since every member of the species from then on is descended from this limited number of progenitors.

The next step is to find something that might cause widespread deaths – usually a catastrophe like the eruption of a supervolcano or an asteroid impact. The genetic studies can narrow down the time frame of the population bottleneck somewhat, and geologists can pinpoint the dates of massive eruptions and impacts fairly accurately. If the dates coincide, you might be onto something.

The third major clue is evidence that the catastrophe did things that would lead to mass die-offs. A huge eruption can cause a prolonged cooling effect, aka "volcanic winter," aka the name of my next band. Alternately, the injection of massive amounts of CO2 into the atmosphere can lead to a runaway greenhouse effect, not to mention the settling of toxic compounds over a wide area. All of these effects are geologically preserved, and can be found, measured and dated. If the whole thing lines up with your bottleneck and your catastrophe, you've got a pretty solid case for an extinction event.
In fact, a recent study found just such evidence for the end-Triassic extinction, caused by a series of massive eruptions in north-central Pangaea, and recently completed studies into the Chicxulub impact all but confirm that a massive impactor was indeed responsible for the extinction of the dinosaurs.

But what about humans? There is one near-extinction event that is fairly well-known, although it remains controversial. Roughly 70,000 years ago, give or take a few thousand years, an enormous eruption occurred in what is now Sumatra, leaving behind Lake Toba (the crater lake pictured above). The eruption coincides with a population bottleneck that is often cited as the reason for the relatively low genetic diversity across Homo sapiens sapiens. Research suggests as few as 2,000 humans were left alive by the eruption and its aftereffects.
A recent paper in the Proceedings of the National Academy of Sciences found another population bottleneck much farther back in human history. Genetic studies found that 1.2 million years ago there were as few as 55,000 members of genus Homo, including pre-human hominids like Homo erectus and Homo ergaster. This one is interesting because we don't have solid evidence of a catastrophic event during that period, so we're not sure what might have caused the population crash or where to look for more evidence.

The really interesting thing about a population bottleneck is the effect it has on evolution. With a small population, mutations get passed through a very large percentage of the species' members. Detrimental mutations could be devastating and lead to outright extinction. Beneficial mutations, however, could cause fairly fast shifts in the population. And if you imagine some kind of tribal arrangement in which a few dominant males were responsible for a lot of the procreation going on, this situation becomes even more pronounced. An entirely new species might be created within a few generations. Anthropologists have proposed that such bottlenecks were responsible for the rapid development of hominids.

A catastrophe induced bottleneck has another factor affecting evolution. It isn't just a bottleneck, it's a bottleneck under pressure. The kinds of dire circumstances that you can imagine would follow a supervolcanic eruption take "survival of the fittest" to a much higher level. Now, that beneficial mutation (say a larger brain that makes it easier to hunt sparse game and build crude shelters) still spreads through a large percentage of the species, but in addition, every genetic line without that mutation dies off (or moves away to somewhere they can hack it). The result: rapid speciation.

When you're in the world building phase of your SF magnum opus, keep speciation in mind. If a planet is not geologically active, it might have homogeneous flora and fauna, or else some other reason why there are diverse species present. After all, giant volcanoes aren't the only reason speciation happens (anything that puts a species under pressure, including other species, works too). On the other hand, a planet prone to sudden, rapid ecological changes might be a good place for sentience to emerge. Any environment that puts species under constant survival pressure and places a premium on adaptability might tend to create intelligent creatures. Sort of like ours did.












The reason why our European Albinos (by way of Central Asia) have so little genetic diversity, is because most of them are the Albinos of only "ONE" Black population: our Caucasian phenotype Black brothers in India - the Dravidians.

The reason why our Mongol Albinos and Mulattoes have so little genetic diversity, is because they derived from the Albinos of our extinct Mongol phenotype Black brothers, the Jomon and Shang, and our now almost extinct Black brothers, the now Mulatto Ainu. Please see the China section for clarification.


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