Environments of evolutionary adaptedness (EEA)
Many people think of the environment of evolutionary adaptedness (EEA) as the ecological and social conditions of a Pleistocene hunter-gatherer. But the EEA is not a specific place or time. It is the statistical composite of selection pressures that pushed the alleles coding for an adaptation to fixation. It is, therefore, an adaptation-specific concept, such that the EEA for one adaptation may be different from that for another. For example, the EEA for color vision consists of the conditions of terrestrial illumination, which have been relatively constant for hundreds of millions of years. In contrast, the EEA for male parental investment in humans, which involved hunting, pair-bonding, etc, is relatively recent, perhaps 2 million years.
The concept of the EEA is among the most important (and misunderstood) in evolutionary psychology. For a detailed discussion of why it is important, see:
Tooby, J. & Cosmides, L. (1990). The past explains the present: Emotional adaptations and the structure of ancestral environments. Ethology and Sociobiology, 11, 375-424. (PDF)