Chapter 22

• Population thinking is a way of thinking that emphasizes the importance of variation among individuals in a population; the opposite of typological thinking, which ignores variation or considers it unimportant.
• Morphology is the overall shape and appearance of an organism and its component parts.
• Evolution is the theory that all organisms on Earth are related by common ancestry and that they have changed over time, and continue to change, via natural selection, genetic drift, gene flow, and mutation. (2) Any change in the genetic characteristics of a population over time, especially a change in allele frequencies.
• Natural selection is the process by which individuals with certain heritable traits tend to produce more surviving offspring than do individuals without those traits, often leading to a change in the genetic makeup of the population. A major mechanism of evolution. The only evolutionary process that produces adaptation.
• Tuberculosis is a disease of the lungs caused by infection with the bacterium Mycobacterium tuberculosis.
• A fossil is any physical trace of an organism that existed in the past. Includes tracks, burrows, fossilized bones, casts, and so on.
• A fossil record is all of the fossils that have been found anywhere on Earth and that have been formally described in the scientific literature.
• Extant species is a species that is living today.
• Genetic correlation is a type of evolutionary constraint in which selection on one trait causes a change in another trait as well; may occur when the same gene(s) affect both traits.
• Acclimatization is a change in an individual’s phenotype that occurs in response to a change in natural environmental conditions.
• Structural homology is similarities in adult organismal structures (e.g., limbs, flowers) that are due to inheritance from a common ancestor.
• Fitness is the ability of an individual to produce viable offspring relative to others of the same species.
• Acclimation is a change in a study organism’s phenotype that occurs in response to laboratory conditions.
• A natural experiment is a situation in which a natural change in conditions enables comparisons of groups, rather than a manipulation of conditions by researchers.
• Descent with modification is the phrase used by Darwin to describe how species that lived in the past are the ancestors of species existing today, and that species change through time. See evolution.
• A phylogenetic tree is a branching diagram that depicts the evolutionary relationships among species or other taxa.
• Extinct species is a species that no longer exists.
• Homology is similarity among organisms of different species due to shared ancestry. Features that exhibit such similarity (e.g., DNA sequences, proteins, body parts) are said to be homologous. Compare with homoplasy.
• Artificial selection is deliberate manipulation by humans, as in animal and plant breeding, of the genetic composition of a population by allowing only individuals with desirable traits to reproduce.
• Sedimentary rocks are a type of rock formed by gradual accumulation of sediment, particularly sand and mud, as in riverbeds and on the ocean floor. Most fossils are found in sedimentary rocks.
• A theory is an explanation for a broad class of phenomena that is supported by a wide body of evidence. A theory serves as a framework for the development of new hypotheses.
• Genetic homology is similarity in DNA nucleotide sequences, RNA nucleotide sequences, or amino acid sequences due to inheritance from a common ancestor.
• A vestigial trait is a reduced or incompletely developed structure that has no function, or reduced function, but is clearly similar to functioning organs or structures in ancestral or closely related species.
• Fitness trade-off, in evolutionary biology, is an inescapable compromise between two traits that cannot be optimized simultaneously. Also called fitness trade-off.
• A transitional feature is a trait that is intermediate between a trait observed in ancestral (older) species and the homologous trait observed in derived (younger) species.
• A geologic time scale is the sequence of eons, eras, and periods used to describe the geologic history of Earth.
• Developmental homology is a similarity in embryonic form or developmental processes that is due to inheritance from a common ancestor.