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The diameter of the aperture determines the intensity of light admitted. archeology: The study of human history and prehistory through the excavation of sites and the analysis of physical remains, such as graves, tools, pottery, and other artifacts.
The pupil of a human eye is a self-adjusting aperture. archetype: The original form or body plan from which a group of organisms develops.
These all develop through an embryo that is enclosed within a membrane called an amnion.
The amnion surrounds the embryo with a watery substance, and is probably an adaptation for breeding on land.
acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weightlifter).
adaptive radiation: The diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological niches (for example, Darwin's finches).
The term can also be applied to larger groups of organisms, as in "the adaptive radiation of mammals." adaptive strategies: A mode of coping with competition or environmental conditions on an evolutionary time scale.
Species adapt when succeeding generations emphasize beneficial characteristics.
Also used to describe the process of genetic change within a population, as influenced by natural selection.
adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it.
antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.