Shellfish & the human bottleneck
How shellfish saved the human race:
Turns out, somewhere between 130,000 to 190,000 years ago, the human species was reduced to less than 1000 breeding individuals–just a few thousand people in total. Ancient, naturally driven climate change pushed our species to the brink, said Curtis Marean, Ph.D., a professor with the Institute of Human Origins and the School of Human Evolution and Social Change at Arizona State University.What saved us? According to Marean, the answer may be “shellfish”.
“They’re a great source of protein,” he said. “And shellfish are immune to colder ocean temperatures. In fact, when the water gets colder, those populations go up.”
Marean used climate models to pinpoint locations in Africa where human hunter-gatherers could have hunkered down during a long glacial period that dried out the continent and expanded deserts. Of the four-to-six possible locations, he focused in on an area along the coast of South Africa.
This is probably wrong. Though one of the many ideas about this period in human history have to be right. And there’s always the tricky problem of falsification and testing alternative hypotheses when it comes to models of human evolution. From what I know humans are a relatively homogeneous species which underwent some sort of demographic expansion within the last 100,000 years. The tacit assumption seems to be that the proto-modern African lineage nearly went extinct, and then bounced back, possibly due to an exogenous shock. My own question: why couldn’t it just be that a few bands simply exterminated or marginalized all the other African lineages? This is an assumption by many about modern humans as they expanded into Eurasia, more or less, so why not in Africa? Humans can certainly reproduce up to the Malthusian limit. In 1800 1.2 million humans were resident in New England, the vast majority of whom were descended from the 20,000-30,000 who arrived in the 1630s. And remember that the reproductive population is going to be a fraction of the census size.
I could speculate on what gave a small subset of African humans an advantage, but I’ll leave that to the comments.
Labels: Human Evolution
Couldn’t the “exogenous shock” that allowed the bounce-back itself be the extinction of other lineages? That is the explanation I’ve heard for the expansion of mammals after dinosaurs were killed off by the asteroid.
The explanation I’d heard before for the human bottleneck was a supervolcanoe.
I like Loren Cordain’s paper on the topic. He is inclined towards early humans scavengings animal brains (for the long chain fatty acids) and marrow bone (for the fat). The problem with eating fish is the protein toxicity ceiling at 40% of calories.
ion%20Final%20PDF.pdf
http://www.thepaleodiet.com/articles/Encephalizat
The continent seems too big for a few small bands to control it, expecially with the technology they had.
Does it bother anybody else that these human bottleneck theories always end with the conclusion that it was caused by envirronmental hardship rather than genetic advantage?
It makes little to no sense that the smartest hominids on the planet (our immediate ancestors) dwindled down to near extinction from a climate crash when these have been demonstrated to be regular events. It makes far more sense that a mental threshhold was crossed by the very smartest individuals within a hunter gatatherer group that allowed for far greater food collection by the whold group. That is all it would take for the nearly moderns to sweep accross Africa and then the world. A long series of food collection strategies can be speculated upon to be part of an eventual world domination by a small group capable of a three part process of 1) feeding itself more succcsessfully 2) reproducing more successfully and 3) expansion because of numerical advantage in any fight.
And that 1.2 million forms a disproportionate part of current American ancestry. So the 20,000-30,000 people who arrived in the 1630s should form a very large part of modern ancestry.
Is this a general principle for any non-Malthusian societies in the recent past? Can we expect a large portion of Latin American ancestry to go back to a few tens of thousands of conquistadores?
Does it not seem likely that a small group of people would have interbred with others they encountered in their expansion?
Other than on small islands (where there were fairly few people to kill in the first place) I can’t recall any cases where entire groups were exterminated without any interbreeding — especially by only a few thousand people.
Does it not seem likely that a small group of people would have interbred with others they encountered in their expansion?
What about outliers of The Hobbit on Flores? The descendents of, say, the Demanji [sp?] people of Georgia, etc? This sounds a bit like the bottleneck needed for a mitochondrial Eve and tends to have a kumbayah tincture about it, or whatever….