Key Revolutions in Human History and Evolution

Key Revolutions in History

• Three primary revolutions shaped history: Cognitive Revolution (70,000 years ago), Agricultural Revolution (12,000 years ago), and Scientific Revolution (500 years ago).
• Cognitive Revolution initiated complex communication and social structures.
• Agricultural Revolution led to sedentary lifestyles and population growth.
• Scientific Revolution advanced knowledge and technology, fundamentally altering humanity's path.

Species and Classification

• Species are groups of similar individuals that can interbreed, producing fertile offspring.
• The term genus groups related species that share a common ancestor, with the plural being genera.
• Lions, tigers, and leopards are classified under the genus Panthera, while humans belong to the genus Homo.

Human Ancestry and Evolution

• Humans (Homo) evolved from Australopithecus around 2.5 million years ago in East Africa.
• Australopithecus translates to "southern ape".
• Homo erectus thrived for 2 million years in East Asia, marking it as a resilient human species.
• Homo soloensis, meaning "Man from the Solo Valley," lived in isolation on Java.
• Homo floresiensis evolved to about 1 meter tall, adapting to the environment of Flores island.

Brain Size Evolution

• An average mammal weighing 60 kg has a brain size of approximately 200 cm².
• Early humans (2.5 million years ago) had a brain size of around 600 cm².
• Modern Sapiens exhibit a brain size ranging from 1200 to 1400 cm².
• The brain of Homo sapiens constitutes 2-3% of total body weight but consumes 25% of energy at rest.

Early Human Tools and Hunting

• Early stone tools were primarily used for cracking bones to access marrow.
• Regular hunting of large game by several human species began around 400,000 years ago.
• Homo sapiens dominated the food chain approximately 100,000 years ago.

Use of Fire

• The earliest evidence of fire usage dates back to 800,000 years ago, with regular use emerging around 300,000 years ago.
• Burning forests provided charred animals, nuts, and tubers.
• Cooking with fire improved hygiene and reduced chewing time significantly (from 5 hours to 1 hour).
• Cooking led to shorter intestines as the energy demand decreased, reallocating resources to the brain.

Human Population and Interbreeding

• The human population was about 1 million around 150,000 years ago.
• The "Interbreeding Theory" suggests that early humans who migrated from East Africa interbred with other species, shaping modern populations.
• Europeans and Middle Easterners are primarily a mix of Sapiens and Neanderthals.
• East Asians (Chinese and Koreans) have genetic contributions from both Sapiens and Erectus.

Competing Theories of Human Evolution

• Two main theories explaining the relationship between Sapiens and other species are the "Interbreeding Theory" and the "Replacement Theory".
• Replacement Theory posits that Sapiens had little attraction to other species, leading to competition and extinction of non-Sapien populations.

Genetic Legacy

• Neanderthal DNA constitutes 1-4% of the genetic makeup of people in Europe and the Middle East.
• 6% of Melanesian and Australian DNA is derived from Denisovan ancestry.
• The last Neanderthals became extinct approximately 30,000 years ago, while the last Homo floresiensis disappeared around 12,000 years ago.