Re: Paleosols of the Turkana Basin

"firstjois" <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> "Philip Deitiker" <[EMAIL PROTECTED] > wrote in message
> news:[EMAIL PROTECTED]

Jonathan Guy Wynn
American Journal of Physical Anthropology
("Early View", i.e. not yet published)

> : Influence of Plio-Pleistocene aridification on human
> : evolution: Evidence from paleosols of the Turkana Basin,
> : Kenya
> :
> :
> : Abstract
> : New stable carbon isotope measurements, coupled with
> : paleoprecipitation estimates, both from Plio-Pleistocene
> : paleosols of the Turkana Basin, Kenya, provide a
> : high-resolution record of aridification and increasing C4
> : biomass during the past 4.3 Ma. This aridification trend is
> : marked by several punctuations at 3.58-3.35, 2.52-2, and
> : 1.81-1.58 Ma, during which the running mean and variance of
> : 13C and paleoaridity estimates increase, suggesting that the
> : proportion of C4 biomass increases in savanna mosaics during
> : periods of heightened aridity. Increase in C4 biomass during
> : these aridification events not only increases the proportion
> : of open habitats, but increases the spatial neg-entropy, or
> : heterogeneity of the ecosystem. The aridification events
> : identified correspond to intervals of increased turnover,
> : but more importantly, increased diversity of bovids.
> : Although the record of hominins from the Turkana Basin lacks
> : the temporal resolution and diversity of the bovid record,
> : the aridification intervals identified are marked by similar
> : increases in the diversity and turnover of hominins. These
> : results support the hypothesis that hominins evolved in
> : savanna mosaics that changed through time, and suggest that
> : the evolution of bovids and hominins was driven by shifts in
> : climatic instability and habitat variability, both
> : diachronic and synchronic.
> 
> I'd comment on this if I understood what the heck it was talking about.

Jois:
  If you have access to Wiley Interscience, you might try this
for the full article:
http://www3.interscience.wiley.com/cgi-bin/fulltext/104539349/HTMLSTART

  From the full article:

CONCLUSIONS       

At least three episodes of aridification in the Turkana Basin
Plio-Pleistocene are marked by increases in spatial and temporal
neg-entropy of open and closed vegetational habitats (at 3.58-3.35,
2.52-2, and 1.81-1.58 Ma).
This observation by no means provides definitive answers to the many
questions related to the causality of climate in human evolution.
It does, however, highlight the potential utility of a basin-scale,
high-resolution record of diachronic and synchronic habitat
variability established from paleosol isotopic data.
It is suggested that a series of such long-term geographically and
chronologically constrained datasets will be able to distinguish the
roles of diachronic and synchronic variability.
Although the hominid record of the Turkana Basin still lacks the
temporal resolution necessary, a preliminary interpretation of the
developing data suggests that modern hominins evolved their unique set
of generalized adaptations during several such cycles of waxing and
waning in the ecological entropy of savanna ecosystems during an
overall trend towards increased aridity.
Those best adapted to nonspecialization of resources were most capable
of surviving through evolutionary pruning events, while other habitat
and dietary specialists were tied to particular habitats with
relatively short ecological life spans.
This trend of generalist selectivity uniquely characterizes the
adaptive abilities of modern humans, which are distinguished from
other hominins by strategies towards more resourceful exploitation of
a variety of habitats, at the margins of existence.
In summary, the course of human evolution may be seen as an increasing
trend towards more rapid short-circuiting of the laborious process of
natural selection, through increases in the human ability to exploit
and conquer new and varied habitats.

  High C4 values are characteristic of arid grasslands.
  This, and soil type, suggests to the author that 
timing of periods of aridity correlates well with 
speciation and other evolutionary developments in hominids, 
meaning that we probably evolved in response conditions in 
a terrestrial, occasionally grassland-dominated, African environment.

  Hoping that this helps,
Daryl Krupa