Glossary .........................................................................................
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.
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
