Transcript Effect of Climate on Human Evolution

Effect of Climate on Human
Evolution
Class: ATOC 530
Presenter: Jennifer Hayek
Date: October 25th 2006
Articles Referenced
• “Environmental Hypotheses of Pliocene Human
Evolution” by Richard Potts
• “Plio-Pleistocene African Climate” by Peter B.
deMenocal
• “Late Cenzoic Moisture History of East Africa” by
Martin H. Trauth, Mark A. Maslin, Alan Deino and
Manfred R. Strecker
• “Climate Change and Human Evolution” by Anna
K. Behrensmeyer
Main Idea of Talk
• Understand climate’s influence on human
evolution in general, and in particular
during the late Cenozoic era with focus on
the Pliocene epoch.
“Environmental
Hypotheses of Pliocene
Human Evolution”
Scope of Article
• Looks at how environmental change
(Climate dynamics in particular) and
human evolution coincided during
Pliocene.
• Looks at how environmental conditions in
East Africa affected mammalian fauna
during same time.
Evolutionary Change in
Pliocene hominins
Hominins: name of the taxonomy that
humans, chimpanzees and their common
ancestors come from.
Evidence of Past Environments
1. Deap Sea oxygen isotopes records of benthic
foraminifera, during colder periods lighter
oxygen evaporated more.
2. African dust records
3. Mediterranean sapropels, dark areas enriched
by large quantities of Fe, S, Si, Ti, Ba
compared to Al, tell about the quantity of
precipitation at different times.
4. Stable isotope and pollen evidence obtained
from hominin areas
Geological History
The Cenozoic Era
Adaptive Environmental
Hypotheses of Human Evolution
3 Adaptive Environmental
Hypotheses
1. The environment having no connection to
evolutionary change, therefore, there may be
evolutionary change even when the
environment is not changing (stable).
2. Evolutionary change happens in small periods
of time where the environment is changing in
one direction.
3. Evolutionary change mainly happens when the
environment is going through highly variable
periods (changes back and forth)
Result of Adaptive Hypothesis
• Lineages (adaptations) now differ
in their ability to endure
environmental fluctuation.
Species Turnover
Environmental Hypotheses
Turnover Hypotheses are hypothesis that
deal with origination and extinction of
multiple clades (biological taxa).
Hypotheses:
• It Happens quite quickly due to climatic
change.
• It Happened gradually, constant turnover
Biogeographic Hypothesis
• Faunal Community formation as well as
break up due to large climatic or tectonic
events.
Hominins during the Pliocene
• Hominins may have begun in the Miocene
age, before the Pliocene, several hominin
lineages originated and went extinct during
the epoch although exact dates of
everything is very uncertain.
Examples of hominins during era: Homo,
Australopithecus and Paranthropus
Adaptive Changes in Pliocene Hominins
1. Mobility: known due to changing limb
proportions, object transport by
toolmakers and biogeographic spread
between regions.
2. Foraging: known by accumulation of
flaked stone and hammers.
3. Diet: known by changing dental
proportions, use of tools to access food
from large animals.
Global Climate Events during Pliocene
•
Climate went from warmer temperatures
“Pliocene Warm Period” to Northern
Hemisphere Glaciation around 2.8 Ma.
However, there was higher climate variability
after 2.8Ma.
Evidence: looking at evaporation of oxygen
isotopes
Cause: Change in period of climate oscillation
from more orbital precession (19-23kyr/period
to obliquety (41kyr/period).
African Pliocene Climate
•
•
•
One addition to the global climate is that
there was also high-aridity moisture
variability periods and low-aridity
variability periods, increase in aridity and
change in arid-moist cycles.
Evidence: dust records
Cause: Modulation of precession of
orbital eccentricity (hypothesis).
African Pliocene Climate
• African Monsoon: Peaks in moisture every
20 kyrs.
• Evidence: Sapropels, dark layers enriched
in organic carbon and elements Fe, S, Si, Ti,
Ba compared to Al
• Cause: African Monsoon from precessional
periods of high precipitation which
discharged from the Nile into the
Mediterranean.
Habitat of Hominins
• Different Hominins species lived quite
differently, early in the Pliocene period
hominins lived more in woodland and
forest, later on a shift towards open
vegetation.
• This change in habitat which effected their
evolution was linked to climate.
Conclusions
• There are specific adaptations that can be
associated with changes in environment
even though it is hard to go from
correlation to cause effect.
• Certain characteristics seen in Hominins
are thought to be due to “Variability
Selection” (Hypothesis C from before).
Variable Selection: adaptation evolved due
to increased environmental variability.
Conclusions
Examples of Adaptations due to Environmental
Variability:
• Earliest bipedal motion (using two legs over 4)
• Earliest tool/food transport as adaptation to
wider variability in vegetation and in food
availability.
• Stone tool making correlated with high
variability in animals.
Conclusions
• During the Pliocene, there is still much to
be learned about climate variability and it’s
effect on species turnover as well as on
adaptive changes.
• Lack of research done so far, not very
good space or time accuracy.
• Although, it's very interesting to see evenly
a moderately understood interdesciplinary
link between such important fields.