amphibians: The class of vertebrates that contains the frogs, toads, newts, and salamanders.
The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land.
Then, even if circumstances change such that it no longer provides any survival or reproductive advantage, the behavior will still tend to be exhibited -- unless it becomes positively disadvantageous in the new environment.
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).
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).
adaptation: Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment.
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.
The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water.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.In a diploid cell there are usually two alleles of any one gene (one from each parent).Within a population there may be many different alleles of a gene; each has a unique nucleotide sequence.
antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.