Effect of Climate on Human Evolution

1. Class: ATOC 530 Presenter: Jennifer Hayek Date: October 25th 2006 Effect of Climate on Human Evolution

2. 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

3. 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.

4. “Environmental Hypotheses of Pliocene Human Evolution”

5. 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.

6. Evolutionary Change in Pliocene hominins Hominins: name of the taxonomy that humans, chimpanzees and their common ancestors come from.

7. Evidence of Past Environments • Deap Sea oxygen isotopes records of benthic foraminifera, during colder periods lighter oxygen evaporated more. • African dust records • 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. • Stable isotope and pollen evidence obtained from hominin areas

8. Geological History

9. The Cenozoic Era

10. Adaptive Environmental Hypotheses of Human Evolution

11. 3 Adaptive Environmental Hypotheses • The environment having no connection to evolutionary change, therefore, there may be evolutionary change even when the environment is not changing (stable). • Evolutionary change happens in small periods of time where the environment is changing in one direction. • Evolutionary change mainly happens when the environment is going through highly variable periods (changes back and forth)

12. Result of Adaptive Hypothesis • Lineages (adaptations) now differ in their ability to endure environmental fluctuation.

13. 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

14. Biogeographic Hypothesis • Faunal Community formation as well as break up due to large climatic or tectonic events.

15. 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

16. Adaptive Changes in Pliocene Hominins • Mobility: known due to changing limb proportions, object transport by toolmakers and biogeographic spread between regions. • Foraging: known by accumulation of flaked stone and hammers. • Diet: known by changing dental proportions, use of tools to access food from large animals.

17. 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).

18. 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).

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.