Table 1.

Transitions in human environmental and interpopulation interactions through time

Transition, time	Major change
Prehistoric transition, millions of years ago	From tree-dwelling to savannah, hunter-gatherer
Historic transitions
•first (local), 5000–10,000 years ago	Settlements, crop and livestock domestication
•second (continental), 1000–3000 years ago	Intracontinental military and commercial contacts
•third (intercontinental), from AD 1500	European exploration and imperialism
•fourth (global), today	Globalization, urbanization, climate change