Glossary
Note: Though some of the terms de¿ned below are widely used, some are used in speci¿c senses in this course. All the de¿nitions below refer to the ways that terms are used in this course. absolute dates: Precise dates on a universal time scale, as opposed to relative dates, which merely give a date relative to the age of some other event. accretion: The process by which planets were formed, as materials orbiting the young Sun gathered together through collisions or gravitational or electrostatic attraction into larger and larger bodies within each orbit. acquired characteristics: Characteristics acquired by an organism during its lifetime and therefore not inherited by its offspring. adaptation: One of the three fundamental features of living organisms; the capacity of living organisms to slowly change from generation to generation so as to maintain their ability to ¿t into their changing environments (see also metabolism, reproduction). Afro-Eurasia: One of the four major “world zones”; it includes the linked African and Eurasian landmasses. Agrarian civilizations: Large communities of hundreds of thousands or even millions of people, based on farming, with cities and tribute-taking states.
Glossary
Agrarian era: One of the three great eras of human history; the era of human history in which most people lived as agriculturalists and most resources were generated through agriculture; roughly from c. 10,000 B.C.E. to c. 1700 C.E. agriculture: A way of exploiting the environment by increasing the productivity of those plant and animal species most bene¿cial for human beings. A form of symbiosis, it generally results, over time, in genetic changes 240
