Toba Catastrophe: Ancient Near Human Extinction Event That Has Changed the World
The population Bottleneck Effect is a theory that assumes that reduction in the genetic diversity and the gene pool as such of a population is associated with the passage of a critical period during which, for various reasons, there is a critical decline in its numbers, followed by a recovery.
What impact can the bottleneck effect have on populations? Such a reduction may lead to dramatic changes in absolute and relative allele frequencies of genes. Due to this, the scientists consider this effect as the factor of the evolution of the population.
Stages according to the Bottleneck Effect theory
- Firstly, a given population has high genetic diversity due to favorable and comfortable environmental conditions, its abundance, and a wide range of habitats.
- In the second stage, the population becomes extinct, its numbers dwindling to a few individuals of the population. The gene pool is becoming depleted. The population decline can occur in certain periods (for each species of the population comes a season unfavorable for the continuation of the genus) or once as a result of catastrophes.
- The final stage is when the population starts to increase again, but the initial genetic diversity of the population is not restored. The conditions for random changes in the population are created by gene drift. Some small populations are also prone to the process of inbreeding.
You may ask which one of these processes describes the Bottleneck Effect? The answer is that all these processes are the parts of the one effect that can lead both to extinction and evolution of the population.
The naming of this effect (bottleneck) precisely describes the way of showing the population size. Once schematically depicted the size of the population at a certain point in time as an ellipse or horizontal bar, and the numbers at subsequent points in the same way, but proportionally higher above the first depiction, resemble a narrowing of the bottle at the top, which graphically resembles the neck of the bottle.
Real Examples of the Bottleneck Effect
Passing through the bottleneck is characteristic of many insect species populations, whose numbers decrease sharply in the autumn-spring period. For example, Drosophila melanogaster populations dramatically decrease during the winter time and recover annually in summer.
Toba Catastrophe Theory
Toba supervolcano catastrophe – a super volcanic eruption that occurred years ago on Lake Toba, which is located in Sumatra, Indonesia. The super-eruption of the Toba volcano in Sumatra, which occurred about 72,000 years ago, is considered to be the most powerful of all the times. Toba threw out 2,800 cubic kilometers of rock in a single explosion. Today, in its place is a volcanic lake more than 80 kilometers long.
This eruption was recognized as one of the largest known eruptions on Earth. According to the hypothesis, this ancient near-human extinction event caused a global volcanic winter of 6-10 years and possibly a 1000-year cooling.
The fact is that the Toba catastrophe is the best scientifically studied super-eruption of all time. In 1993, popular science journalist Anne Gibbons assumed that this catastrophic eruption is the best human population Bottleneck example.
The journalist was supported by many scientists, for instance, Stephen Self from the University of Hawaii at Manoa and Michael Rampino of New York University agreed with the theory and continued the research to find more proof. In 1998, the theory was further developed by Stanley Ambrose of the University of Illinois. Other researchers see no evidence between the eruption of Toba Volcano and the bottleneck.
According to paleontologists, the event, which is an example of the Bottleneck Effect, has led to a strong decrease in the average temperature on Earth and the disappearance of many animal and plant species. And according to one of the hypotheses, it was through the difficulties of this period that prehistoric man became a Homo sapiens, as we are today. Huge calderas left by eruptions indicate that at least three or four catastrophic eruptions have occurred on Toba in the last two million years.
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