Chapter 14: The Origin of Species
14.1 – The origin of species is the source of biological diversity
1. What is speciation?
The process by which one species splits into two or more species
Darwin envisioned the history of life as a tree, with multiple branchings from a common trunk out to the tips of the youngest twigs
2. How is microevolution different from speciation?
Microevolution involves evolutionary changes within a population
Speciation occurs when a population changes enough that it diverges from its parent species and becomes a new species.
14.2 – There are several ways to define a species
3. List and briefly describe the four different concepts of species.
1) Biological: species = group of populations whose members have the potential to
interbreed in nature and produce fertile offspring (which can also reproduce)
2) Morphological: based on physical traits such as shape, size, and other features of
morphology (form). Advantage: can be applied to asexually reproducing species and
fossils. Disadvantage: relies on subjective criteria
3) Ecological: identifies species in terms of their ecological niches, focusing on unique
adaptations to particular roles within a community
4) Phylogenetic: defines species as the smallest group of individuals that share a
common ancestor and thus form one branch on the tree of life
4. What is meant by reproductive isolation? Why is it so important when discussing speciation?
The prevention of gene exchange between different species.
It is an essential factor in the evolution of many species.
5. What is meant by a hybrid when discussing biological species? Give an example.
Hybrid is an offspring created by the mating of clearly distinct species
Ex: grizzly bear X polar bear = grolar bear hybrid.
Much more common in plants than animals.
animal hybrids
eaten any hybrid fruits lately?
14. 3 – Reproductive barriers keep species separate
6. What is a reproductive barrier?
A biological feature of an organism preventing individuals of different species from breeding
This isolates the gene pools of 2 species.
7. Differentiate between prezygotic vs postzygotic barriers. List and describe the main types of each.
 Prezygotic: prevent mating or fertilization
o Habitat – lack of opportunities to encounter each other
 EX/snakes occupying different habitats in same area, one in water, one on land
o Temporal – breed at different times or seasons

Ex/ plants flowering at different seasons or open flowers at different times of day
o Behavioral – Failure to send or receive appropriate signals
 EX/different mating calls for birds
o Mechanical – physical incompatibility of reproductive parts
 EX/floral characteristics fit their pollinators
o Gametic – molecular incompatibility of eggs and sperm or pollen and stigma
 EX/ Sea urchin gametes have specific surface proteins that will only allow binding to surface proteins of same
species
 Postzygotic: operate after hybrids form
o Reduced hybrid viability – offspring development is impaired due to interactions of parental genes
 EX/hybrid offspring do not develop fully or are frail and don’t survive long enough to reproduce
o Reduced hybrid fertility – hybrids are vigorous, but can’t produce viable offspring
 EX/horse + donkey = mule (sterile)
o Hybrid breakdown – hybrids are viable and fertile, but their offspring are feeble or sterile
 EX/2nd generation rice hybrids are sterile
Blue footed Booby courtship dance
14.4 – In allopatric speciation, geographic isolation leads to speciation
8. Explain the process of allopatric speciation. (Allo = other; Patra = fatherland)
Geographic barrier isolates a population  prevents gene flow between two populations.
Separated gene pools can
follow their own evolutionary
course.
**HHMI short film The
Lizards in an Evolutionary
14.5 – Reproductive
populations diverge
9. Provide one example of research involving populations that
becoming reproductively isolated.
Starch fruit flies vs maltose fruit flies. Flies raised on
introduced to each other, they mated more frequently
source
14.6 – Sympatric speciation takes place without geographic isolation
10. How does sympatric speciation occur?
New species arises in the same geographic area as parent species.
Can occur when gene flow is reduced by:
1) Polyploidy
2) habitat differentiation (speciation b/c of different food sources in same area)
3) sexual selection (females choosing mates based on colors).
Origin of Species:
Tree (18 min)
barriers can evolve as
are in the process of
different media were
with flies from same food
11. How do tetraploid plants arise?
Accidents in cell division resulting in diploid gametes.
When plant self-fertilizes, the new offspring are tetraploid.
12. Briefly explain how polyploid species are created by hybridization of
two species.
Hybrid created from haploid gametes from two different species
reproduces asexually, followed by subsequent errors in cell division that
produce chromosome duplications that result in a diploid set of
chromosomes. This new species can reproduce sexually.
14.7 – The origin of
13. What percentage of
polyploidy speciation?
most plant species can be traced to polyploidy speciation
living plant species are descendants of ancestors formed by
80%
14. How many different
Three species (or 4)
T.monococcum + Wild
T.turgidium + T.tauschii
species of plants does bread wheat, T.aestivum come from?
Triticum = T.turgidium (emmer wheat used for pasta)
= T.aestivium
14.8 – Isolated islands are often showcases of speciation
15. Explain the process of speciation resulting from adaptive radiation.
 When founder populations colonize a new area and change significantly as
natural selection occurs while adapting to new surroundings.
 Because they are reproductively isolated, speciation can occur.
 Later, a few may leave this population  migrate to a new island and could
change enough to become another new species.
16. What features of the Galapagos Finches give evidence for adaptive radiation?
Beaks have become adapted to the different food sources, and they have adapted to
being either tree dwellers or ground dwellers.
*HHMI short film The Beak of the Finch (16 min)
14.10 – Hybrid zones provide opportunities to study reproductive isolation
17. What is a hybrid zone?
Regions in which members of different species meet and mate, producing at
least some hybrid offspring.
This helps to answer questions about what happens when separated
populations of closely related species come back into contact with one
another
18. Briefly explain the three possible outcomes of a hybrid zone over time.
 Reinforcement – Reproductive barriers are reinforced when they overlap
 Fusion – Speciation process reverses, and the two hybrids fuse into one
 Stability – hybrids continue to be produced while each species maintains its own integrity
14.11 – Speciation can occur rapidly or slowly
19. Compare punctuated equilibrium to gradualism
PE: long periods of little change (equilibria)
interrupted (punctuated) by relatively short periods
of sudden change.
Gradualism: divergence gradually over long periods
of time.
Fossil evidence suggests punctuated equilibrium,
but gradualism can’t be ruled out b/c the fossil
record is incomplete.