A population bottleneck is not specifically defined by Marean in his article, but it is possible to infer the definition. Due to his reference to a “dramatic population decline”, it appears a bottleneck is a significant drop in a species’ population, and perhaps in genetic diversity (2012, pg. 52-59). In the article, he describes a significant drop in the population of Homo sapiens “between 195,000 and 123,000 years ago,” due to a “climate catastrophe.” What his research seems to have confirmed is that the particular region he studied had a combination of plants and seafood that were available consistently enough and in adequate quantities to support a population of humans when they were dying off in other parts of the world due to an ice age. This may have caused a relative lack of genetic diversity in the human family tree as this population could not have readily interacted with populations that died off and diversified genes.
When I first read the article, I didn’t think the quartzite and silcrete tools you mentioned were as important as food sources in the stabilization of the population, but the more I read it the more convinced I am that they are significant. I think they show the sophistication these people had that allowed them to be so adaptable. I wonder if there was something different about these people than others who perhaps were not able to exploit similar food sources in other locations on the continent.
I also think the microclimate that included hardier sources of carbohydrates was key to the survival of the population of humans that made up our ancestors. I found it interesting that they did not necessarily live right on the shoreline, which allowed them to survive the changes in the shoreline due to the changing climate. It is interesting that they likely tracked the changes in the tides and made trips to the shoreline for food based upon those observations.
Marean, C. W. (2012). When the sea saved humanity. Scientific American, 22(1s), 52-59.