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Humans and Pre-Industrial Climate The black curve shows the northern hemisphere temperature in a climate model. Michelle Letendre, Evan Wise, Chance Snow, Mary James, Sara Smith, Cristy Echaves Climate and Human Evolution Humans evolved in Africa Radiometeric dating Evidence of Human Evolution 5 Distinctive Developments Initial branching off from primate ape Onset of bipedalism Use of stone tools Branching of the pre-human Development of large brains line into genus Homo Appearance of Human Ancestors Humans evolved from a small shrew-like mammal Primitive apes evolved Human ancestors & chimpanzees branched off Molecular Biology Walking Upright Hominins Hominidae 4.3 myr ago 3.6 myr ago The development to walk is still argued today Use of Stone Tools Used to butcher dead animals “killer ape” hypothesis Cutting = Use of all the animal Butchering = Diet change A natural evolutionary development Stone = Digging Appearance of Homo Ancestral australopithecines Paranthropus Homo erectus Stone tools and use of intellect & imagination = Frequent & vast movement Brain Size Braincase – part of the skull that houses the brain Hominid Braincases Growth by Volume Age (Myr ago) Braincase (cm3) Homo sapiens 0.2 – 0 1100 – 1500 Homo erectus 2.4 - 1.8 800 – 1000 Australopithecus 4.1 - 3.1 400 - 500 Type Unusually rapid compared to many evolutionary changes Braincase volume has 3x Did Climate Change Drive Human Evolution? • Savanna Hypothesis • Sediments from Indian and Atlantic Ocean Support this Hypothesis Atmospheric CO2 • A long term decrease in atmospheric CO2 could have been a factor in the change in vegetation • There was a change from C3 to C4 carbon on all continents Volcanic Plateaus • Vegetation shifted from forest to grassland • Cooling of Western Indian Ocean This may be more complicated than we think… Hominins lived in many different environments (woodlands, grasslands, river margins) This leads to a different Hypothesis… The The Variability Selection Hypothesis: Rapid evolution occurred because rapidly changing climate put new demands on our ancestors, which favored those who were more adaptable. • Links have been found between glaciation and the appearance of the genus Homo • Pollen records from East Africa support this Hypothesis • Records from the Eastern and Southern Plateaus of Africa support the hypothesis as well. Problems with the Variability Selection Hypothesis… • It is believed that the ice sheets would’ve had little effect on the African climate. • Summer monsoons continued for millions of years. No trend toward larger or smaller oscillations. Aliasing • Different signals become indistinguishable when sampled, or aliases • Also refers to distortions or artifacts that appear in signal reconstructions Sparse Fossil Records Composed of easily dissolved calcium phosphate Bad preservation of remains in acid rich soils of rain forests Brief snapshots of human evolutionary history Aliasing = Misrepresentation Specimens may not be representative of the population Depiction of inaccurate long-term trends Aliasing = Misrepresentation Aliasing is a Problem A formidable concern with just one sample every 100,000 years or so Erroneous indications of significant developments (e.g. first evidence of walking and use of tools) Complicates correlation of relative timing between climate changes and first use of new traits Volcanic Plateaus Vegetation shifted from forest to grassland Cooling of Western Indian Ocean First Evidence of Agriculture •Fertile Crescent oAbandonment hunting/gathering oDomestication of: cattle, livestock, barley, etc. • Association of Deglaciation and Agriculture = Hypothesis about cause and effect link Proposed Cause and Effect Links • The changing conditions made agriculture more favorable • The Younger Dryas – Climatic reversal Climate change is hypothesized to be a major contributing factor to the deterioration of early civilizations Changing Saharan Monsoons coincided with the movement of peoples throughout the Sahara and the development of the early Egyptian dynasties. The Mayan Classic Period 300 AD-1,000 AD Data Collected from lake beds and stalactites indicate severe drought events during the declining years of the Maya. Anasazi Climate Change and the Anasazi Resource Depletion Coupled with Changing Climate Did Humans Cause Megafaunal Extinction? Megafauna comes from the ancient Greek word mega meaning “Large” and the new Latin word fauna meaning “animal” 50,000 years ago more than 150 genera of mammals larger than ~100 pounds existed 10,000 years ago there were fewer than 50 left Australia During the most recent glaciation (est. 50,000 year ago) many marsupials and nonmarsupials became extinct Just before the glaciation humans had first entered Australia through southeast asia because of the low seas The humans used fire to help hunt these animals and leads scientist to believe the humans were the primary cause of extinction Climate One of the major explanation of the megafaunal extinction in North America is climate change The deglaciation caused strong summers Scientists have been critical of climate hypothesis because many of the mammals went extinct over 12,500 years ago Overkill Hypothesis The idea that human hunting caused extinction of the megafauna The hunting could have been from the either from the first human arrival in America or by the first appearance of new hunting technology or strategy The first humans inhabited America 12,500 years ago. They crossed into Alaska by using land bring from Asia Around the same time, 12,500 years ago, a new technology appeared which allowed for humans to hunt bigger game Criticism of the Overkill Hypothesis Were there enough people to cause extinction of the megafauna? o Large mammals have slow reproduction o Humans worked in team to drive animals to their death over step cliffs. So many animals died but only a fraction were used for food and clothing. Many carnivores went extinct but how? o With the prey that carnivores eat going extinct the carnivores would decrease their population. How did the megafauna we see today survive? Diluvial Hypothesis tries to explain the worldwide flood and the widespread deposit Black Sea Flood Hypothesis Early Anthropogenic Hypothesis Proposed by William Ruddiman States that cyclic variations in CO2 and CH4 driven by Earth’s orbital changes during the 350,000 yrs predict a decrease in CO2 and CH4 but anomalies in the data show an increase in CO2 occurring 8,000 yrs ago as well as a rise in CH4 occurring 5,000 years ago. Deforestation began 8,000 yrs ago leading to an increase of CO2. Large scale rice cultivation began in India and China 5,000 yrs ago producing higher levels of CH4. CO2 & CH4 Influences Further Evidence for the Early Anthropogenic Hypothesis 5, 000 years ago the Monsoon weekend across the Sahara reducing CH4 emissions from wetlands. Arctic summers became cooler England in 1086 was 85% arable land was pasture or crops, 15% remaining forest. Rice irrigation began in SE Asia 7,000-6,000 years ago increasing considerably 5,000 years ago. 2,000 years ago 50 million people were living in China Circulation Models support this idea indicating that a new glaciation would already be underway. Critiques of the Early Anthropogenic Hypothesis Argue that there were not enough humans to effect greenhouse gases in a substantial way. Anomaly can not be accounted for even if all the forests in Southern Eurasia were cut down centuries before. Chapter Highlights What are the 5 distinctive developments of humans? What issue does the effect of aliasing raise? Where was the first evidence of agriculture found? What was the main contributing factor to the abnormal high precipitation during the height of the classic Mayan period? What is the general idea of Early Anthropogenic Hypothesis? Chapter Highlights What is the main difference between the Savanna Hypothesis and the Variability Selection Hypothesis? What were the two hypothesis for the extinction of the megafauna? Evidence points more toward the support of the Savanna hypothesis rather than the Variability selection hypothesis.