15.1: New Species Evolve
Objectives:
1. Describe the biological
species concept.
2. Distinguish b/w micro and
macroevolution.
3. List types of reproductive
barriers b/w species.
4. Explain how geographic
isolation and adaptive
radiation contribute to
species diversity.
5. Summarize models for the
tempo of speciation.
Vocabulary
Biological Species
concept
Macroevolution
Speciation
Reproductive Isolation
Geographic Isolation
Adaptive Radiation
Punctuated Equilibrium
When do new species evolve?
Evolution of Human Species
Hominids
Humans
Neanderthal
Most Recent Common Ancestor
Homo heidelbergenesis, 600 - 300 ka (thousands)
Homosapiens and Neanderthal evolve from
Homo erectus
1.8 - 1.3m.y.a
Homo Habilis 2.3 - 1.4 m.y.a
Australopithicus, 3.2 m.y.a
“Lucy”
SPECIATION
• = formation of new species.
Species = a group of organisms that
breed with one another and produce
fertile
offspring.
• The gene pools of two populations must
become separated.
• When the members of two populations
cannot interbreed and produce fertile
offspring, reproductive isolation has
occurred and speciation will result.
Micro
vs. Macroevolution
Change allele frequencies
W/IN A POPULATION.
• Small changes fr.
generation to generation
• Result: What species look
like can change over time.
*Does NOT change branches
on EVOLUTIONARY
TREE
Large scale changes in
biological record (fossils)
• Origin of new species
• Extinction of species
• Evolution of new features
(backbones, wings, etc)
• Result: Increase in # of
species
*Changes branches on
EVOLUTIONARY Tree
Speciation: Reproductive
Barriers
Species separate when they cannot interbreed.
Reproductive Isolation: Condition that keeps 2 species from
interbreeding
1. Timing Issues: 2 species have diff. Breeding seasons
2. Behavior: Different courtship or mating behaviors
3. Habitat: Surface water v. deep water
4. Not anatomically compatable
Speciation: Geographic
Barriers
Species separate when they cannot interbreed.
Geographic Isolation: Separation of populations by
barriers like mountains

Over time isolated populations change through
microevolution (natural selection acting on variations
to produce adaptations)
Divergent v. Convergent
Evolution
Divergent
• One species gives rise
to many species
• Also known as
adaptive radiation
• Many species with
common ancestor
• Many homologous
structures
Convergent
• Similar looking species
that do not have a
common ancestor
• Similar behavior and
appearance due to
environmental
similarities
• Many analogous
structures
Divergent Evolution (Adaptive)
Convergent Evolution (Adaptive)
Coevolution:
The evolution of one species is directly influenced
by the evolution of another
Rate of Speciation
Two Models
Gradualism v. Punctuated Equilibrium
Punctuated Equilibrium
• Slow background
evolution (stasis) is
interrupted by rapid
bursts of change
• Rapid/Abrupt bursts
of change usually
occur after a mass
extinction
– Abrupt : w/in a few
thousand years
Seen in fossil record after mass
extinctions.
Speciation in Darwin's
Finches
Speciation of Darwin’s Finches
• founding of a new
population
• geographic isolation
• changes in new
population's gene pool
• reproductive isolation
• ecological competition
STEP 1: Founders Arrive
•A few finches,
“species A”, travel
from S. America to
one of the
Galápagos Islands.
•There, they
survive and
reproduce.
STEP 2: Geographic Isolation
•Some birds from
species A cross to a
second island.
•The two
populations no
longer share a gene
pool.
STEP 3: Changes in the Gene Pool
•Seed sizes on the
second island
favor birds with
large beaks.
•The population
on the second
island evolves into
population “B”,
with larger beaks.
STEP 4: Reproductive Isolation
• If population B birds cross back to
the first island, they will not mate
with birds from population A.
• Populations A and B are separate
species.
STEP 5: Ecological Competition
• As species A and B compete for available seeds on
the first island, they continue to evolve in a way that
increases the differences between them.
• A new species—C—may evolve.