Chapter 24 Study Guide:
Vocabulary:
Word Roots:
allo- = other
-metron = measure
ana- = up
-genesis = origin, birth
auto- = self
poly- = many
clado- = branch
hetero- = different
macro- = large
paedo- = child
post- = after
sym- = together
-patri = father or country
Key Terms:
Allopatric speciation: A mode of speciation induced when an ancestral population becomes
segregated by a geographic barrier or is itself divided into two or more geographically isolated
subpopulations.
Biological species concept: Definition of a species as a population or group of populations whose
members have the potential to interbreed in nature and produce viable, fertile offspring, but are not
able to produce viable, fertile offspring with members of other populations.
Ecological species concept: Defining species in terms of ecological roles (niches).
Macroevolution: Evolutionary change above the species level, including the appearance of major
evolutionary developments, such as flight, that we use to define higher taxa.
Microevolution: Evolutionary change below the species level; change in the genetic makeup of a
population from generation to generation.
Morphological species concept: Defining species by measurable anatomical criteria.
Phylogenetic species concept: Definition of a species as a set of organisms with a unique genetic
history—that is, as one branch on the tree of life.
Polyploidy: A chromosomal alteration in which the organism possesses more than two complete
chromosome sets.
Postzygotic barrier: Any of several species-isolating mechanisms that prevent hybrids produced by
two different species from developing into viable, fertile adults.
Prezygotic barrier: A reproductive barrier that impedes mating between species or hinders
fertilization of ova if interspecific mating is attempted.
Punctuated equilibrium: In evolutionary theory, long periods of apparent stasis (no change)
interrupted by relatively brief periods of sudden change.
Speciation: The origin of new species in evolution.
Species: A group whose members possess similar anatomical characteristics and have the ability to
interbreed.
Sympatric speciation: A mode of speciation occurring as a result of a change in the genome of a
subpopulation, reproductively isolating the subpopulation from the parent population.
Chapter 24 Important Points:
 New species arise through speciation events driven by various selection pressure
 One of the most common ways to define a species is using the biological species concept
which maintains members of a species must naturally reproduce and produce viable, fertile
offspring
o There are limitations to the biological species concept so other methods to define
species exist
 Hybrids, in terms of speciation, refers to offspring of 2 different species
 Reproductive isolation between species can be maintained at many levels
o Prezygotic barriers such habitat isolation, timing of mating, mating behavior
differences contributing to sexual selection, incompatible mating appendages and
gametes that can not combine for chemical or physical reasons
o Postzygotic barriers assume a zygote is formed by it may have reduced viability so it
does not survive or if it does, it is sterile or subsequent hybrid offspring have
reduced viability
 Speciation can occur with physical, geographical barriers which keeps gene pools separate
(allopatric) or by other means even when species are not isolated (sympatric)
 In sympatric speciation, species may exploit smaller areas of their habitats called ecological
niches which can drive differences between populations eventually to the point of speciation
or sexual selection may subdivide populations so that eventually this behavioral isolation
leads to other reproductive barriers
o In plants, duplication of entire sets of chromosomes can lead to polyploidism in
which new species have stable, new chromosome numbers compared to original
species
 Hybrid zones exist in the middle ground between where 2 separate species overlap so that
mating can take place
 Different scenarios can develop from hybrid zones
o Reinforcement: Original species are selected for and hybrids do not do very well so
that the original species continue to diverge
o Fusion: Hybrids are very fit and the 2 original species may eventually become one
single species
o Stability: Original species stay separate but occasional hybrids continue to form in
the hybrid zone but don’t increase or decrease in number

The length of time it takes for a new species to evolve is very variable with some speciation
events being very quick if certain selection factors favor speciation
o Species that appear quickly in a geological time frame in the fossil record are said to
follow the punctuated equilibrium pattern of speciation while others form very
gradually over much longer periods of time