Speciation and Evolution Key Definitions

Speciation

The formation of a new species via evolution

Prezygotic barrier

Anything that causes a hybrid zygote to never exist in the first place

Postzygotic barrier

Anything that prevents a hybrid that exists to die and/or not reproduce

Stratigraphic layer

A layer in the earth that has fossils from a certain time period

Eon, Era, Period, Epoch, Age

The categorizations of super long times (in order)

Gradualism

The idea that evolution is always occurring at a slow, gradual rate

Punctuated equilibrium

The idea that evolution occurs in comparatively short bursts (eg, a volcano wipes out a population)

Polyploidy

The heritable trait of having more than two complete sets of chromosomes

Microevolution

Evolutionary change over a small group of organisms over a short period of time (basically always occurring)

Macroevolution

Major evolutionary change, especially over a whole taxonomic group and a long period of time

Hybrid zone

The in-between time where two new species may be able to hybridize

Reinforcement

The hybrids die out, the two new species are reinforced

Fusion

The two species merge back into one

Stability

All three species become stable populations

Reduced hybrid viability

Hybrids do not survive to child-bearing age

Reduced Hybrid fertility

Hybrids can survive, but cannot produce offspring

Hybrid breakdown

Hybrids can survive and produce offspring, but due to a lack of fitness in their environment, will die out within a couple generations

Adaptive radiation

The phenomenon that occurs after a mass extinction where the few remaining extant species thrive

Directional selection

a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype

Stabilizing selection

Evolution that results in the concentration of animals in a population with a certain trait

Disruptive selection

occurs when individuals of intermediate phenotype are less fit than those of both higher and lower phenotype, such that extremes are favored.

Novel characteristics

A trait that arises via mutation or genetic engineering

Plate tectonics

The movement of the Earth's lithosphere

Radioisotopes

Unstable isotopes used in radiometric dating

Radiometric dating

The tool by which we use radioisotopes to determine the age of fossils

Half-life

The time it takes for an isotope to decay halfway

Habitat isolation

Animals in different habitats will not encounter each other and cannot mate

Behavioral isolation

Animals whose behavior isolate them from each other will not mate

Mechanical isolation

Animals who don't have the parts can't successfully mate

Allopatric speciation

Speciation where the species are separated geographically

Sympatric speciation

Speciation where the species are not separated geographically

Sexual selection

The process by which individuals compete for access to mates

Homoplasy

Analogous traits; heritable traits that resemble each other but are not derived from a common ancestor

Ecological species concept

Animals are one species if they have all adapted to the same ecological niche

Phylogenetic species concept

Animals are a species if they are descended from a common ancestor and share defining heritable traits

Morphological species concept

Animals are a species if they share the same observable physical traits with their group

Mate recognition species concept

If the animals can and will mate, they are the same species regardless of other factors

Biological species concept

Animals are a species if they are actually or potentially interbreeding in natural populations

Mass extinction

A time period in which about 75% of the world's species go extinct