All terms in this list:

evolution: descent with modification, change in genetic composition of a population from generation to generation

fossils: remains or traces of organisms from past

strata: layers in sedimentary rock

paleontology: study of fossils

catastrophism: principle that events in the past occurred suddenly and were caused by mechanism different from those operating in the present

uniformitarianism: mechanisms of change are constant over time

adaptation: inherited characteristics of organisms that enhance their survival and reproduction in specific environments

natural selection: process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

artificial selection: when humans modify species by selecting and breeding individuals that possess desired traits

homology: similarity resulting from common ancestry

homologous structures: represent variation on a structural theme that was present in their common ancestor

evolutionary tree: diagram that reflects evolutionary relationships among groups of organisms

convergent evolution: independent evolution of similar features in different lineages

analogous: share similar function, but not common ancestry

biogeography: evidence of evolution, geographic distribution of species

endemic: found nowhere else in the world

genetic variation: differences among individuals in the composition of their genes or other DNA sequences

average heterozygosity: average percentage of loci that are heterozygous

geographic variation: differences in genetic composition of separate populations

cline: a graded change in a character along a geographic axis

population: group of individuals of the same species that live in the same area and interbreed, producing fertile offspring

gene pool: made of all copies of every type of allele at every locus in all members of a population

Hardy-Weinberg Principle: frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

genetic drift: chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next

founder effect: when a few individuals become isolated from a larger population, the smaller group may establish a new population whose gene pool differs from the source popuation

bottleneck effect: sudden change in environment, such as a fire or flood, that may drastically reduce the size of a population

gene flow: transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

relative fitness: contribution an individual makes to the gene pool of the next generation relative to their contributions of their individuals

directional selection: occurs when conditions favor individuals exhibiting one extreme of a phenotype range, thereby shifting a populations frequency curve for the phenotype character in one direction or the other

disruptive selection: occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes

stabilizing selection: acts against both extreme phenotypes and favors intermediate variants, reduces variation and tends to maintain the status quo for a particular phenotypic character

sexual selection: selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates

sexual dimorphism: differences between two sexed in secondary sexual characteristics. ie: size, color, ornamentation, behavior

Intrasexual selection: selection within the same sex, individuals of one sex compete directly for mates of opposite sex

intersexual selection: mate choice, individuals of one sex are choosy in selecting their mates from other sexes

neutral variation: differences in DNA sequence that do not confer a selective advantage or disadvantage

balancing selection: occurs when natural selection maintains two or more forms in a population, includes heterozygote advantage and frequency-dependent selection

heterozygote advantage: if individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygotes

frequency-dependent selection: fitness of a phenotype depends on how common it is in the population

speciation: process by which one species splits into two or more species

microevolution: changes over time in the allele frequencies in a population

macroevolution: broad pattern of evolution above the species level

reproductive isolation: existence of biological factors (barriers) that impede members of two species from interbreeding and producing fertile, viable offspring

hybrids: offspring that result from an interspecific mating

prezygotic barriers: block fertilization from occurring

postzygotic barriers: if sperm cell fertilizes ovum, factors can contribute to reproductive isolation after hybrid zygote is formed

habitat isolation: 2 species that occupy different habitats within the same area may encounter each other rarely, if at all, even though they are not isolated by physical barriers

temporal isolation: species that breed during different times of the day, different seasons or different years can not mix their gametes

behavioral isolation: courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. Some behavioral rituals enable mate recognition- a way to identify potential mates

mechanical isolation: mating is attempted, but morphological differences prevent its successful completion

gametic isolation: sperm of one species may not be able to fertilize egg of another species

reduced hybrid viability: genes of different parent species may interact in ways that impair the hybrids development or survival in its environment

reduced hybrid fertility: hybrids may be sterile. if chromosomes of two parent species differ in number or structure, meiosis in hybrids may fail to produce normal gametes

hybrid breakdown: when first generation hybrids mate with one another or with either parent species, offspring of next generation are feeble and sterile

morphological species concept: characterizes a species by body shape and other structural features; can be applied to asexual and sexual organisms and can be useful even without information on the extent of gene flow

ecological species concept: views a species in terms of its ecological niche, sum of how members of the species interact with the nonliving and living parts of their environment

phylogenetic species concept: defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life

allopatric speciation: gene flow is interrupted when a population is divided into geographically isolated subpopulations

sympatric speciation: speciation occurs in populations that live in the same geographic area

polyploidy: accident during cell division that results in extra sets of chromosomes

autopolyploid: an individual that has more than 2 sets of chromosomes that are all derived from a single species

allopolyploid: fertile polyloid

protocells: droplets with membranes that maintained an internal chemistry from that of their surroundings

ribozymes: RNA that can carry out a number of enzyme-like catalytic functions

radiometric dating: based on decay of radioactive isotopes

half-life: time required for 50% of parent isotope to decay

geological record: study of Earth's history, divided into 3 eons

stromatolites: layered rocks that form when certain prokaryotes bind thin films to sediment together

endosymbiont theory: mitochondria and plastids were formerly small prokaryotes that began living within larger cells

serial endosymbiosis: mitochondria evolved before plastids through a sequence of endosymbiotic events

Cambrian explosion: many animal phyla appeared suddenly in fossils formed early in cambrian period

plate tectonics: continents are part of great plates of Earths crust that essentially float on hot, underlying portions of the mantle

adaptive radiation: periods of evolutionary change in which groups of organisms form new species whose adaptations allow them to fill different ecological roles, or niches, in communities

phylogeny: evolutionary history of a species or group of species

systematics: discipline focused on classifying organisms and determining their evolutionary relationships

taxonomy: how organisms are named and classified

binomial: 2 part format of scientific name

genus: first part of binomial name, which species belongs to

phylogenetic tree: branching diagram of evolutionary history

phylocode: only name groups that include a common ancestor from a common ancestor

branch point: represents divergence of two evolutionary lineages from a common ancestor

sister taxa: groups of organisms that share an immediate common ancestor

rooted: a branch point within the tree represents the most recent common ancestor of all taxa in tree

basal taxon: lineage that diverges early in history of a group and lies on a branch that originates near common ancestor of group

polytomy: branch point from which more than 2 descendant groups emerge

homoplasies: analogous structures that arose independently

cladistics: common ancestry is primary criterion used to classify organisms

clades: groups that include and ancestral species and all of its descendants

monophyletic: consists of an ancestral species and all of its descendants

paraphyletic: consists of an ancestral species and some but not all descendants

polyphyletic: taxa with different ancestors

shared ancestral character: character that originated in an ancestor of taxon

shared derived character: evolutionary novelty unique to the clade

outgroup: species or group of species from an evolutionary lineage that includes species we are studying (ingroup)