Modelling Paleoindian dispersals

Abstract

It is reasonable to expect that the global dispersal of modern humans was influenced by habitat variation in space and time; but many simulation models average such variation into a single, homogeneous surface across which the dispersal process is modelled. We present a demographic simulation model in which rates of spatial range expansion can be modified by local habitat values. The broadscale vegetation cover of North America during the late last glacial is reconstructed and mapped at thousand-year intervals, 13,000-10,000 radiocarbon years BP. Results of the simulation of human dispersal into North America during the late last glacial are presented; output appears to match observed variation in occupancy of habitats during this period (as assessed from discard rates of diagnostic artefacts), if we assume that intrinsic population growth rates were fairly high and that local population densities varied as a function of environmental carrying capacity. Finally, a number of issues are raised relating to present limitations and possible future extensions of the simulation model.

Strong reproductive isolation between humans and Neanderthals inferred from observed patterns of introgression

“…For the 100 × 100 km 2 deme area resolution, the carrying capacity of Neanderthals demes (K N ) was set to a value corresponding to a density of about 0.025 individuals per 1 km 2 (3), including juveniles and older nonreproducing people. Still in keeping with the study by Currat and Excoffier (3), and in agreement with density estimates for Pleistocene hunter-gatherers (28,29), we used a fourfold higher density for modern humans (K H ), which approximately corresponds to 0.1 individual per 1 km 2 . The K values used in the present study thus roughly correspond to those used in our previous simulation study (3), taking into account the fact that the number of gene copies of nuclear DNA is fourfold larger than for mtDNA.…”

Spatial gradients in Clovis-age radiocarbon dates across North America suggest rapid colonization from the north

“…In these regions, initial foraging return rates would have been high but regeneration rates of megafaunal prey would have been very slow [perhaps infinite (7,8,36)] because of low reproductive rates, leading to large home ranges and the rapid geographic expansion of human populations (sensu 31). Similarly, Clovis colonists would have moved rapidly through large river systems (4), such as the Missouri and Mississippi drainages, leading to an initially rapid rate of colonization through the midcontinent, which would have then slowed dramatically as diet breadths broadened with the increased biodiversity of the eastern forests (27,37), and as prey size, abundance, and availability changed (38).…”

Paleoindian demography and the extraterrestrial impact hypothesis

“…It is worth noting that the southern boundary of the Laurentide ice sheet is estimated to have been at or slightly below the 50th parallel Ϸ12,900 cal BP (19). In the region of the Great Lakes it may have dipped as far south as the 45th parallel (19). Therefore, the paucity of radiocarbon-dated occupations in these areas is attributable to the lack of habitable land.…”

“…We ignored the three radiocarbon-dated occupations above 50°of latitude and the four below 30°of latitude. It is worth noting that the southern boundary of the Laurentide ice sheet is estimated to have been at or slightly below the 50th parallel Ϸ12,900 cal BP (19). In the region of the Great Lakes it may have dipped as far south as the 45th parallel (19).…”