Speciation and Evolution

Describes and analyzes speciation, including the processes of adaptive change, adaptive radiation, phyletic gradualism, and punctuated equilibrium

1. Speciation and Evolution:Speciation and Evolution:
The ProcessesThe Processes

2. Defining Species: ReviewDefining Species: Review
•Evolution involves populations, not
Individuals
•Species is a population of organisms
whose members can interbreed under
natural circumstances and reproduce
fertile (viable) offspring

3. How Do New Species Arise?How Do New Species Arise?
•Two fundamental processes give rise to new species:
•Cladogenesis: The splitting off of one species into two
clades, usually because of geographical isolation, but
also because of reproductive isolation.
•Two kinds of species develop by cladogenesis:
•Sympatric Species: Those whose speciation is the
product of geographical isolation
•Allopatric Species: Those whose speciation is the
product of reproductive isolation of population in the same
region.
•Anagenesis: The replacement of an ancestral species by
a daughter species over time; the ancestral species
become extinct.

4. Speciation: Evolution Through Speciation: Evolution Through
CladogenesisCladogenesis
•Cladogenesis:
•Time I: Genes flow freely in region
•Time II: Barrier separates two
populations
•Time III: Mutations change
genotype and phenotype of 2
populations
•Time IV: Two populations cannot
interbreed even with removal of
barrier
•Definition: Branching of one
species into two
•From clade (“branch”) or group
with common evolutionary ancestry.

5. Speciation: Allopatric SpeciesSpeciation: Allopatric Species
•Allopatric speciation
occurs when two populations
are separated by a
geographical barrier (river,
mountain range)
•In this example, three
species of fish have evolved
in separate zones

6. Speciation: Sympatric SpeciesSpeciation: Sympatric Species
•Sympatric species are those
that are separated by a
reproductively isolation
mechanism
•Speciation occurs among
three populations of fish even
though the different species
occupy the same region
•There are several ways for
subspecies to become
reproductively isolated

7. Modes of Reproductive Isolation In Modes of Reproductive Isolation In
SympatrySympatry
•Ecological Isolation: Different populations are separated by
occupy a slightly different niche
•Seasonal Isolation: The breeding season of two closely related
populations do not match.
•Sexual Isolation: One or both sexes of a species initiate mating
behavior that does not act a stimulus to the opposite sex of a closely
related population
•Mechanical isolation: Populations do not mate because of an
incompatibility of the male and female sex organs of the individuals
(extreme example: wolves and Chihuahuas)
•Gamete Isolation: Incompatibility of sex cell with bodily
environment
•Hybrid Infertility or Sterility: Hybrids do not survive or reproduce
(mules)

8. Speciation: Role of Speciation: Role of
MicromutationMicromutation
•Micromutation: Mutations with
•extensive or important phenotypic
results
•Example: Axolotl (species of
salamander)
•This salamander starts life as
tadpole-like larvae, as do other
salamanders
•Axolotl, however, never grows up—
doesn’t sprout mature legs, keeps
its gills, remains aquatic existence.
•Injection of a hormone enables
maturity and to live on land, so that
one mutation can and does create
major change

9. Adaptive Radiation DefinedAdaptive Radiation Defined
•Definition: Evolution and spreading out of
related species into new niches
•Niche: An environment in which an organism is
found and its adaptive response to that
environment
•Generalized Adaptive Radiation: The
adaptation of a species to a wide range of
niches. Homo sapiens is an example.
•Specialized Adaptive Radiation: The
adaptation of a species to a narrow range of
niches.

10. Adaptive Radiation: Favorable Adaptive Radiation: Favorable
ConditionsConditions
•Absence of similar and therefore
competing species
•Occurrence of extensive extinction,
thereby emptying an environment of
competitors
•Adaptive generalization of new group of
related species which enable it to occupy
several niches and displace species
already there.

11. Adaptive Radiation: Absence of Adaptive Radiation: Absence of
Competing SpeciesCompeting Species
•Example: Darwin’s finches on Galápagos
Islands who were blown there by winds from
mainland Ecuador
•Niches opened up for 13 varieties with different
bills, including those that feed on cactus or eat
specific insects in trees
•Others use twig or cactus spine to probe for
insects
•A vampire finch sucks blood from larger birds

12. Finches and Their Adaptive Finches and Their Adaptive
RadiationRadiation
•Ground finches (Geospiza) who are seed and cactus eaters;
•Tree finches (Camarhynchus), who are insect and bud eaters
•Warbler finches (Certhidea) who vary by color.

13. Adaptive Radiation: SpecializationAdaptive Radiation: Specialization
•Definition: Adaptation of a species to a narrow range of
environmental niches
•Example: Again, some species of Darwin’s finches on
Galápagos Islands are examples.
•Medium ground finch was nearly wiped out in the 1977
drought
•Sudden change could eliminate this or others of these
genera and species of finches
•Example: prosimians adapt on in habitats afforded by
Madagascar and are close to extinction.

14. Adaptive Radiation: GeneralizationAdaptive Radiation: Generalization
•Definition: Adaptation of a species to a wide range of
environmental niches
•Examples:
•Mammals spread after the disappearance of dinosaurs 65
m.y.a. and occupied innumerable niches, from grassland
(ungulates) to trees (bats)
•Monkeys with a mixed diet occupied diverse arboreal
(tree) habitats; they displaced the prosimians
•Humans: from frozen north to tropical rainforest or desert
—thanks to culture—are the most generalized primate

15. Types of Evolution: Darwinian or Types of Evolution: Darwinian or
Phyletic GradualismPhyletic Gradualism
•Definition:
•Slow, step-by-step changes over time
•Intermediate forms assume “missing links”
•Darwin postulated this model
•Examples: From monkeys to apes; apes
to hominins (e.g. Lucy); and from early
hominins to modern Homo sapiens

16. Problems with GradualismProblems with Gradualism
•Fossil record does not reveal fine gradations from one lifeform
to a descendant life form: no “missing links.”
•Bipedalism occurred quickly as the fragmentary fossil record
shows.
•Reproductive advantage: do slight changes bestow this
advantage?
•Continuum question: at which point does a population become
two species?
•Sometimes, change can take place rapidly, either through
oscillating selection or punctuated equilibrium

17. Types of Evolution: Oscillating Types of Evolution: Oscillating
SelectionSelection
•Definition: Adaptive variation around a norm rather than
direction in response to environmental variation
•Example: Medium and small ground finch lacked a bill
strong enough to crack tough seeds
•Occurrence of drought selected plants whose seeds had a
tough exterior
•Survival of large, longer-billed finches
•Smaller, shorter-billed finches returned after the climate
returned to normal,
•Shifting bill size and lengths reflected the oscillation of the
environmental conditions.

18. Types of Evolution: Punctuated Types of Evolution: Punctuated
EquilibriumEquilibrium
•Definition: Species tend to
remain stable over time, then,
evolutionary changes occur
suddenly (in terms of centuries or
millennia)
•Causation: Populations may
become fragmented and isolated,
and from there new forms arise
•Small, new populations may
invade a region, and through the
founder effect and better
adaptation, create and spread a
new species
•Example: Archaeopteryx (ancient
bird), a dinosaur with feathers:
suddenly appears and may have
created a new class known as
Aves (birds)

19. Phyletic Gradualism and Phyletic Gradualism and
Punctuated EquilibriumPunctuated Equilibrium
•A summary of gradualism and punctuated equilibrium

20. Pseudoscience and CreationismPseudoscience and Creationism
•Pseudoscience consists of scientifically
testable ideas in form that are taken on
faith even after they are proven as false
•(Scientific) Creationism is the belief in a
literal biblical interpretation of the creation
of earth in six days 6,000 to 10,000 years
ago
•The claim is testable, has been tested,
and has been demonstrated to be false.

21. Counterevidence to CreationismCounterevidence to Creationism
•Existence of strata, such as the Grand Canyon,
accumulated over 2 billion years falsifies the claim that the
earth is only a few thousand years old
•Presence of extinct lifeforms, from fossil fish to dinosaurs,
demonstrate that other forms existed at one time but are
now extinct
•Presence of ancient hominins establish extinct humanlike
creatures that look like us but are not us.
•Both kinds of evidence are abundant

22. ConclusionConclusion
•Species is unit of evolution
•Evolutionary change is more random than
progressive
•Speciation is the basic process of evolutionary
change
•Changes may be gradual or rapid
•Scientific rule: follow the evidence
•Evidence for evolution is overwhelming in the
form of geological strata and fossil lifeforms