analogous structure

a structure in one organism that is similar to that of another organism due to convergent evolution and not shared common ancestry

Cambrian explosion

a biologic event during the Cambrian period when many lineages of organisms first appeared


a taxonomic group that includes an ancestor and all of its descendants

common ancestor

an earlier organism that, through evolution, gives rise to new species that are related

convergent evolution

process by which two species acquire similar features due to similar selection pressures and not shared ancestry

endosymbiotic theory

the idea that eukaryotic cells and their organelles evolved from early cells engulfing prokaryotes


loss of all members of a particular group

fossil record

all the fossilized artifacts taken in the context of their placement within Earth's geological strata

gene pool

the total set of genes of all individuals in a population

homologous structures

structures that are similar due to inheritance from a common ancestor


evolutionary change at or above the species level

mass extinction

the loss of many species because of global environmental conditions


a change in allele frequencies within a population from one generation to the next

phylogenetic tree

a diagram that shows the history of evolutionary relationships among two or more groups of organisms


the evolutionary history of groups of organisms

primordial soup theory

the idea that life began in one of the ancient oceans or another body of water because of the chemical combination in the atmosphere and the influx of energy to make molecules that support life


a self-organizing, spherical collection of lipids proposed as the origin of living cells

radiometric dating

the scientific process of using the half-life of radioactive elements to establish the absolute age of a fossil


the process through which a species evolves into two or more new species


a pattern in which a species in the fossil record shows minimal change over time