1. VOCABULARY Jessica Gómez

5. biogeography the study of the geographical distribution of living organisms and fossils on Earth homologous structure body part that is similar in structure on different organisms but performs different functions analogous structure body part that is similar in function as a body part of another organism but is structurally different vestigial structure remnants of an organ or structure that functioned in an earlier ancestor

7. gene pool the total set of genes, including all alleles, that are present in a population at any one point in time allele frequency proportion of one allele, compared with all the alleles for that trait, in the gene pool

8. normal distribution a distribution of numerical data whose graph forms a bell-shaped curve that is symmetrical about the mean microevolution observable change in the allele frequencies of a population over a few generations directional selection a natural selection process in which one genetic variation is selected and that causes a change in the overall genetic composition of the population stabilizing selection a type of natural selection in which the average form of a trait is favored and becomes more common disruptive selection a type of natural selection in which two extreme forms of a trait are selected

9. genetic drift the random change in allele frequency in a population gene flow the movement of genes into or out of a population due to interbreeding bottleneck effect genetic drift that results from an event that drastically reduces the size of a population founder effect genetic drift that occurs after a small number of individuals colonize a new area sexual selection an evolutionary mechanism by which traits that increase the ability of individuals to attract or acquire mates appear with increasing frequency in a population; selection in which a mate is chosen on the basis of a particular trait or traits

10. Hardy-Weinberg equilibrium condition in which a population’s allele frequencies for a given trait do not change from generation to generation

11. reproductive isolation a state in which a particular set of populations can no longer interbreed to produce future generations of offspring speciation the formation of new species as a result of evolution behavioral isolation isolation between populations due to differences in courtship or mating behavior geographic isolation isolation between populations due to physical barriers temporal isolation isolation between populations due to barriers related to time, such as differences in mating periods or differences in the time of day that individuals are most active

12. convergent evolution the process by which unrelated species become more similar as they adapt to the same kind of environment divergent evolution evolution of one or more closely related species into different species; resulting from adaptations to different environmental conditions coevolution the evolution of two or more species that is due to mutual influence, often in a way that makes the relationship more mutually beneficial extinction the death of every member of a species punctuated equilibrium a model of evolution in which short periods of drastic change in species, including mass extinctions and rapid speciation, are separated by long periods of little or no change adaptive radiation an evolutionary pattern in which many species evolve from a single ancestral species

13. elative dating a method of determining whether an event or object, such as a fossil, is older or younger than other events or objects without referring to the object's age in years radiometric dating a method of determining the absolute age of an object, often by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope isotope an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mas half-life the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope index fossil a fossil that is used to establish the age of a rock layer because the fossil is distinct, abundant, and widespread and the species that formed that fossil existed for only a short span of geologic time geologic time scale the standard method used to divide Earth's long natural history into manageable parts era a unit of geologic time that includes two or more periods period (in geology) a unit of geologic time that is longer than an epoch but shorter than an era epoch smallest unit of geologic time, lasting several million years

14. cyanobacteria bacteria that can carry out photosynthesis endosymbiosis a mutually beneficial relationship in which one organism lives within another

15. Paleozoic era of geologic time (from 544 to 248 million years ago) during which members of every major animal group alive today evolved Cambrian explosion earliest part of the Paleozoic era, when a huge diversity of animal species evolved Mesozoic era during which dinosaurs roamed Earth (from 248 million years ago to 65 million years ago) Cenozoic geologic time period that began 65 million years ago and continues today bipedal animal that walks on two legs primate a member of the order Primates, the group of mammals that includes humans, apes, monkeys, and prosimians; typically distinguished by a highly developed brain, forward-directed eyes and binocular vision, opposable thumbs, and varied locomotion prosimian oldest primate group that includes mostly small, nocturnal primates such as lemurs anthropoid humanlike primate hominid a member of the family Hominidae of the order Primates; characterized by bipedalism, relatively long lower limbs, and lack of a tail; examples include humans and their ancestors