The growth rate in the Homo sapiens population didn’t change, according to Jean-Pierre Bocquet-Appel and his colleagues. What did change was those people were compressed into a smaller area. In Cantabrian Spain, Lawrence Straus noted 18 sites have been located for the Aurignacian era, and 33 in the last glacial maximum. That wasn’t simply a doubling of density: the 18 were spread over 15,000 years while the 33 ranged over 3,000 years.
Simple arithmetic suggests that was one site every 100 years. However, while many locations may have been used only once, La Riera had twenty layers of human occupation. Carbon fragments have been dated to 16,420 years ago in layer 11 of the Asturian cave, to 16,900 years ago in layer 13, and to 17,010 years ago in layer 18. Roughly 240 years or 12 generations passed between each visit between layers 11 and 13. Earlier, bands had stopped there every 55 years.
The scale of human adjustment to climatic change was still vast. Fifty-five years represented more than two 20-year generations. Each stop was a new discovery.
It’s hard to know from marine isotopes if the onset of cold, drought and winds was gradual, sudden, or fluctuated. What we’re learning from global warming today is there can be a long period when undetected changes slowly accumulate that result in sudden cataclysms like the calving of ice sheets.
Before the drought of the 1930s, the western and central parts of Nebraska had different communities of grass. The one was a mixture of tall and short grasses, the other was dominated by blue stem. When the rains failed year after year, western wheat grass took blue stem’s place. The lower-growing blue grama and buffalo grass came with it. In some places, side oats grama became dominant.
While the western mixed prairie was moving east, the west slowly died. First the grass stubble shattered, exposing perennial root crowns to wind and sun. When they died, the remaining mulch of dead leaves blew away, and the lichens and mosses that build soil died. Winds left dirt where once there’d been organic soil.
That transition occurred quickly. The summer of 1933 had been dry. The rains failed in 1934. John Weaver was describing the transformation in 1939 - five years later.
One can take this as an analogy for the process of glacial expansion. Within five years, a 300-mile-wide stretch of land had been altered, its vegetation transformed in the east, destroyed in the west.
By modern calculations, it’s a tad under 400 miles from Ulm near the center of the Aurignacians in Swabia to Mâcon, near a Solutrean center in France. Solutré is item 12 on the map below.
It’s more than 400 miles from Ulm to the Gravettian centers in Moravia. The combined distances are four times the span of change in Nebraska.
It’s unlikely everything happened within a generation. More than likely, some dry years that modified the vegetation alternated with a few years that had enough rain to maintain a status quo. During each dry spell, the line of vegetation moved a little, followed by the animals that depended on it. To the rear, more land was abandoned by Nature.
At the same time the climate was becoming drier, it also was becoming colder. Françoise Delpech noted the horse was the faunal equivalent to side oats grama and western wheatgrass. It adapted "faster than any other species to the most diversified conditions, even the most severe."
Everyone and everything was on the move. At some point, refugees from central Europe must have realized they were being pulled away from their base camps and were becoming more transient, perhaps able to settle for a while in one area, then forced to move again.
There was little they could take with them, beyond their mental attitudes. They were having to adapt every year to changing conditions.
The one thing they maintained was an appreciation for bone as a fuel and implement. Their mental agility would have been reinforced as their constantly changing locations were dictated more by the availability of food rather than by natural resources like flint or burnable trees.
A new technology, the Solutrean emerged about 22,000 years ago in France. The stone points were an adaption of an old insight to a new need. Instead of using a harder rock to chip a form from flint, they used bone or wooden tools to dislodge slivers. Technically the change was from percussion to pressure.
Solutrean techniques spread west to the rivers flowing into the Bay of Biscay. Carbon remains from Laugerie Haute in the Dordogne have been dated to 20,890 years. That’s in the general area of item 9 on the map.
At the same time people from the north and east were moving towards one of the refuges in the south, people in those areas were moving farther south with their particular biomes. Solutrean points have been dated to 21,710 at Les Mallaetes and to 20,170 at Parpalló. Both caves in Valencia are near item 4 on the map.
Notes: Bocquet’s group’s calculations were described in the post for 22 November 2015. The distance from Lincoln, Nebraska to Holyoke, Colorado is 335 miles by interstate 80E.
Clark, Peter U., et alia. "The Last Glacial Maximum," Science 325:710-714:2009.
Delpech, Françoise. "Biostratigraphy of the Solutrean Layers of Laugerie-Haute (Les Eyzies, Dordogne). Archaeological Implications," Paleo 23:105-116:2012.
Straus, Lawrence Guy. "On Maritime Hunter-Gatherers: A View From Cantabrian Spain," Munibe 33:171-173:1981.
_____. "Once More into the Breach: Solutrean Chronology," Munibe 38:35-38:1986.
_____, F. Bernaldo de Quirós, V. Cabrera, and G. Clark. "New Radiocarbon Dates for the Spanish Solutrean," Antiquity 51:243:1977.
Weaver, J. E. and F. W. Albertson. "Major Changes in Grassland as a Result of Continued Drought," Botanical Gazette 100:576-591:1939.
_____ and R. W. Darland. "Grassland Patterns In 1940," Ecology 25:202-215:1944.
Animals:
Horses - Equus caballus gallicus
Grasses:
Bluestems - Andropogon
Buffalo grass - Buchloe dactyloides
Grama, blue - Bouteloua gracilis
Grama, side oats grama - Bouteloua curtipendula
Wheat grass, western - Agropyron smithii, now Pascopyrum smithii
Graphics: Sémhur, "Carte de Localisation de la Culture Homo Sapiens du Solutréen, Environ entre -20 000 et 15 000," uploaded to Wikimedia Commons, 28 October 2009.
No comments:
Post a Comment