Evolution & Diversity
cambrian explosion
A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geologic history; recorded in the fossil record about 545-525 million years ago
polyploidy
A chromosomal alteration in which the organism possesses more than two complete chromosome sets.
phylogenetic species concept
A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.
ecological species concept
A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.
morphological species concept
A definition of species in terms of measurable anatomical criteria.
intrasexual selection
A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.
population
A group of individuals of the same species that interbreed, producing fertile offspring
serial endosymbiosis
A model of the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells.
prezygotic barriers
A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted
phyla
A taxonomic category. are divided into classes, example: chordata
ribozymes
An enzymatic RNA molecule that catalyzes reactions during RNA splicing.
autopolyploid
An individual that has more than two chromosome sets, all derived from a single species.
homoplasies
Analogous structures that evolved independently
homeotic genes
Any of the genes that control the overall body plan of animals by controlling the developmental fate of groups of cells.
bottleneck effect
Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.
sister taxa
Groups of organisms that share an immediate common ancestor and hence are each other's closest relatives
orders
In classification, the taxonomic category above family, example: carnivora
family
In classification, the taxonomic category above genus, example: felidae
classes
In classification, the taxonomic category above order, example: mammalia
intersexual selection
Individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex, also called mate choice.
directional selection
Natural selection that favors individuals at one end of the phenotypic range.
stabilizing selection
Natural selection that favors intermediate variants by acting against extreme phenotypes
balancing selection
Natural selection that maintains two or more phenotypic forms in a population (balanced polymorphism)
phylocode
Only names groups that include a common ancestor and all of its decendants.
endosymbiosis
Process through which early prokaryotic cells are thought to have engulfed other, smaller cells and eventually incorporated them as organelles; these cells evolved into modern-day eukaryotes.
stromatolites
Rock made of banded domes of sediment in which are found the most ancient forms of life: prokaryotes dating back as far as 3.5 billion years.
sexual selection
Selection based on variation in secondary sex characteristics, leading to the enhancement of sexual dimorphism.
homologous structures
Structures in different species that are similar because of common ancestry.
relative fitness
The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.
geologic record
The division of Earth's history into time periods, grouped into three eras: Archaean, Proterozoic, Phanerozoic, and further subdivided into eras and epochs.
phylogeny
The evolutionary history of a species or group of related species
taxon
The named taxonomic unit at any given level of classification
catastrophism
The principle events in the past occured suddenly and were caused by different mechanisms than those operating today
branch points
The representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor
paedomorphosis
The retention in an adult organism of the juvenile features of its evolutionary ancestors.
pangaea
The supercontinent formed near the end of the Paleozoic era when plate movements brought all the landmasses of Earth together.
binomial
The two-part latinized name of a species, consisting of genus and specific epithet.
evolutionary tree
a branching diagram that reflects a hypothesis about evolutionary relationships among groups of organisms
phylogenetic tree
a branching diagram that represents a hypothesis about the evolutionary history of a group of organisms
microevolution
a change in a population's gene pool over successive generations; evolutionary changes in species over comparably brief periods of time
mutation
a change in the nucleotide-base sequence of a gene or DNA molecule
frequency-dependent selection
a decline in the reproductive success of individuals that have a phenotype that has become too common in a population
allopolyploid
a fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chormosomes
hybrid zone
a geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry
cline
a graded change in a trait along a geographic axis
species
a group of organisms so similar to one another that they can interbreed and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such groups
clades
a group of species that includes an ancestral species and all its descendants
genetic drift
a process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next, effects are most pronounced in small populations
reinforcement
a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing the chances of hybrid information, likely to occur only if hybrid offspring are less fit that members of the parent species
postzygotic barriers
a reproductive barrier that prevent hybrid zygotes produced by two different species from developing into viable, fertile adults
domains
a taxonomic category above the kingdom level; examples: Archaea, Bacteria, and Eukarya
genus
a taxonomic category above the species level, example: panthera
kingdoms
a taxonomic category the second broadest after domain, example: animalia
gene pool
all of the alleles for all the loci in all the individuals that make up a population
cladistics
an approach to systematics in which organisms are placed into groups called clades based primarily on common decent
disruptive selection
both forms at extreme endfavors are favored, intermediate forms eliminated
protobionts
collection of abiotically produced molecules surrounded by a membrane or membrane-like structure
biological species concept
definition of a species as a population or group of populations whose members can breed with one another in nature and produce fertile offspring
evolution
descent with modification; the idea that living species are descendants of ancestral species that were different form present-day ones
rooted
describing a phylogenetic tree that contains a branch point representing the last common ancestor of all taxa in the tree
geographic variation
differences between the gene pools of separate populations or population subgroups
taxonomy
discipline of classifying organisms and assigning each organism a universally accepted name
macroevolution
evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time
heterochrony
evolutionary change in the timing or rate of an organism's development
sympatric speciation
formation of a new species within the same geographic area
allopatric speciation
formation of new species in populations that are geographically isolated from one another
neutral variation
genetic variation that does not appear to provide a selective advantage or disadvantage
heterozygous advantage
greater reproductive success of heterozygous individuals compared to homozygotes, tends to presever variation in gene pools
analogous
having characteristics that are similar because of convergent evolution
polytomy
in a phylogenetic tree, a branch point from which more than two descendant taxa emerge. A polytomy indicates that the exoutionary relationships among the descendant taxa are not yet clear.
punctuated equilibria
in the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change
strata
layers of sediment that have formed over millions of years
sexual dimorphism
marked differences between the secondary sex characteristics of males and females
radiometric dating
method used to determine the age of rocks and fossils using the rate of decay of radioactive isotopes
adaptations
modification of an organism or its parts that makes it more fit for existence under the conditions of its environment
hybrids
offspring that results from the mating of individuals from two different species or two true-breeding varieties of the same species
mass extinction
period of time when global environmental changes lead to the elimination of a large number of species throughout Earth
fossils
preserved remains of once-living organisms
speciation
process by which new species are formed
endemic
referring to a species that is confined to a specific, relatively small geographic area
vestigial structures
remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species.
artificial selection
selective breeding of domesticated plants and animals to produce offspring with desired genetic traits
fossil record
shows that past organisms differed from present-day organisms and that many species have become extinct
analogy
similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with that same trait
homology
similarity in characteristics resulting from a shared ancestry
systematics
study of the diversity of organisms to classify them and determine their evolutionary relationships
half-life
the amount of time it takes of a sample of a radioactive isotope to decay
molecular systematics
the comparison of nucleic acids or other molecules in different species to interfere relatedness
hardy-weinberg equilibrium
the condition describing a non-evolving population
adaptive radiation
the development of many different forms from an originally homogeneous group of organisms as they fill different ecological niches
convergent evolution
the evolution of similar features in independent evolutionary lineages
reproductive isolation
the existence of biological factors (barriers) that impepde members of two species from producing viable, fertile hybrids
average heterozygosity
the percent, on average, of a population's loci that are heterozygous in members of the population
uniformitarianism
the principle stating that mechanisms of change are constant over time
hardy-weinberg principle
the principle that frequencies of alleles and genotypes in a population remain the constant from generation to generation, provided that Medelian segregation and recombination of alleles are at work
natural selection
the principle that, among the range of inherited trait variations, those contributing to reproduction and survival will most likely be passed on to succeeding generations.
continental drift
the slow movement of the continental plates across Earth's surfce
paleontology
the study of fossils
biogeography
the study of the past and present distribution of species
founder effect
when a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool isn't reflective of the source population
