Lec 9 - History, Humans, Climate Flashcards
What five major developments are there in human evolution?
- branching from other apes
- bipedalism (4mya)
- Use of stone tools (2.5mya)
- Emergence of Homo genus (2mya)
- Development of large brains (2mya)
What factors likely drove human evolution?
- social factors
- tool/innovation
- climate
What 2 hypotheses explain how climate may have impacted our recent evolution?
- Savannah Hypothesis
- Variability Selection Hypothesis
What is the Savannah Hypothesis?
- human evolution was driven by long-term drying of African climate
- tropical rainforests became semiarid grassland
- fragmentation meant greater need for travel over ground, resourcefulness
- drying began 4-6mya (dated by dust)
Savannah hypothesis: what drove long-term drying in Africa?
- volcanic plateaus block wet air from Indian Ocean
- cooling of Indian Ocean meant less moisture in air
- Tibetan plateau uplift = more monsoons, drives dry air into Africa
Why doesn’t the Savannah Hypothesis explain everything?
- hominids haven’t shown preference for one biome over another, no obvious preference for savannahs
What is the Variability Selection Hypothesis?
- rapid evolution was driven because rapid habitat change favoured individuals/groups that were adaptable
Why doesn’t the Variability Selection Hypothesis explain everything?
fossil record of human evolution is pretty sparse, hard to put together a timeline of the rate of evolution
(ie hard to test hypothesis!)
When is the first evidence of agriculture?
12kya
What impacts did climate change have on early civilization?
- deglaciation is associated with permanent settlements/agriculture
- Younger Dryas would have hindered this transition
Give an example of how the Younger Dryas period might have impacted human civilization
- low latitude regions where water was scarce, the dryness in the YD
- Egyptian dynasties relying on Nile floodplain
- Mayan civilization dispersing during drought
- Anasazi peoples abandoning cliff dwellings during drought
What impacts did early H. sapiens have on our environment?
- megafauna extinctions
- cliamte (CO2 and CH4 from forest clearing and agriculture)
What might explain the extinction of megafauna at the end of the LGM?
- major climate changes - large animals = susceptible to environmental unpredictability
- overkill hypothesis - improved hunting skills/increased human populations
What evidence is there for the Overkill Hypothesis?
- timing of megafauna extinctions in Americas and Australia lines up with humans crossing over
Are GHG levels post-LGM explained by human activity?
probably not - the increase in CO2 and CH4 was too big to be explained by deforestation, burning, agriculture, rice irrigation etc
