catastrophe. Luck is always a factor in evolutionary survival, but just as you’re not likely to break the bank in Las Vegas, a very populous species is not likely to get knocked out of the game by normal bad luck. Of course, the universe being what it is, there’s also such a thing as extreme bad luck, which comes along from time to time and can whittle formerly robust populations down very quickly. This most often occurs during situations of climate disruption or the sudden introduction of very successful new species into an ecosystem, throwing the continued viability of other species into contention. The “bottleneck” refers to the shape of the graph of population versus time, which shows a “narrow point” of low population like the neck of a bottle before expanding again - or collapsing.
All extant organisms have numerous population bottlenecks in their evolutionary past, and these bottlenecks have determined the nature of life as it exists today. Even we humans have faced such bottlenecks, not once but many times. For instance, when the Toba super- volcano erupted 71k years ago, it created many cold years without normal summers, reducing the total human population of Earth to perhaps 15,000 individuals 90 … not enough
to fill 25% of a modern football stadium. Genetic evidence shows that over the past two million years our population has even fallen far lower multiple times. Genetic Bottlenecks are caused by population bottlenecks, but do not recover the way populations do. To understand this, we need to realize that a healthy population of organisms contains a storehouse of potential variability. While evolution is generally said to proceed through a process of beneficial mutations proving adaptive, what is less-commonly discussed is that these nonlethal mutations tend to accumulate very slowly during long periods of stable conditions and populations, when they neither help nor hurt the animals much. When environmental change occurs, the entire population has on hand, so to speak, the inborn flexibility of individuals
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