Study: Human Evolution Forced by Chaotic Landscape
December 27, 2012 1:45 PM
Adversity breeds strength -- and perhaps human intelligence
It's a widely held hypothesis that ecological and climatological changes had a crucial driving role in evolution throughout history. Now
Penn State University
and her graduate student, Clayton Magill, have put forth an intriguing study, which suggests that chaos in the ecosystem of East Africa drove
2 million years ago.
I. Life on the Chaotic Savanna
Mr. Magill comments, "The landscape early humans were inhabiting transitioned rapidly back and forth between a closed woodland and an open grassland about five to six times during a period of 200,000 years. These changes happened very abruptly, with each transition occurring over hundreds to just a few thousand years."
To examine the ecological transition that coincided with this crucial phase of
the researchers traveled to the
in northern Tanzania, collecting lake sediments. Filtering the sediments of different ages, they performed biochemical analysis looking for fossilized chemical traces of grasses and trees.
Specifically, they sifted through sediments looking for leaf waxes, hardy biochemicals that tend to resist breakdown and survive, even over millions of years. By performing gas chromatography and mass spectrometry analyses on the various waxes, the researchers were able to pinpoint both the foliage and composition to within a couple centuries.
Biochemical analysis of local sediments in a Tanzania gorge have offered key clues as to the evolutionary path of mankind's hominid ancestors. [Image Source: Gail Ashley]
What they discovered was that the "Great Drying", which is widely proven to have occurred in Africa around 3 million years ago, was not as much of a one-way process as was previously thought. Rather, the sediments showed that the local ecosystem appears to have gone through a chaotic transition period in which the climate would fluctuate between wet and dry, before eventually gravitating fully to drier savanna.
To better understand the source of such strange and chaotic cycling, the researchers used statistical and mathematical models to formulate a hypothesis on the causes.
Explains Professor Freeman, "The orbit of the Earth around the sun slowly changes with time. These changes were tied to the local climate at Olduvai Gorge through changes in the monsoon system in Africa. Slight changes in the amount of sunshine changed the intensity of atmospheric circulation and the supply of water. The rain patterns that drive the plant patterns follow this monsoon circulation."
"We found a correlation between changes in the environment and planetary movement. We find complementary forcing mechanisms: one is the way Earth orbits, and the other is variation in ocean temperatures surrounding Africa."
II. Adversity Breeds Evolved Intelligence
The chaos would obviously cause great stress on hominids living in the region forcing them to
adapt to different food sources
, different landscape, and different predators. Mr. Magill and Professor Freeman suggest this was a key driver of the evolution of human intelligence.
Comments Mr. Magill, "Early humans went from having trees available to having only grasses available in just 10 to 100 generations, and their diets would have had to change in response. Changes in food availability, food type, or the way you get food can trigger evolutionary mechanisms to deal with those changes."
"The result can be increased brain size and cognition, changes in locomotion and even social changes -- how you interact with others in a group. Our data are consistent with these hypotheses. We show that the environment changed dramatically over a short time, and this variability coincides with an important period in our human evolution when the genus Homo was first established and when there was first evidence of tool use."
The papers suggest chaotic climate changes triggered the rise of human intelligence.
[Image Source: Pace J. Miller]
The research was published as a
[abstracts] in the prestigious peer-reviewed journal
The Proceedings of the National Academy of Sciences
). Among the other researchers working on the team was
earth and planetary sciences professor
. The research was funded by a
National Science Foundation
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