ammonoid: Extinct relatives of cephalopods (squid, octopi, and chambered nautiluses), these mollusks had coiled shells and are found in the fossil record of the Cretaceous period.
amniotes: The group of reptiles, birds, and mammals.
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.
amino acid sequence: A series of amino acids, the building blocks of proteins, usually coded for by DNA.
allopatric speciation: Speciation that occurs when two or more populations of a species are geographically isolated from one another sufficiently that they do not interbreed. There are 20 main amino acids in the proteins of living things, and the properties of a protein are determined by its particular amino acid sequence.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.aperture: Of a camera, the adjustable opening through which light passes to reach the film.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.