The document summarizes key concepts about the origin of species from Charles Darwin's theory of evolution by natural selection. It discusses Darwin's observations in the Galapagos Islands that led to his ideas, defines microevolution and macroevolution, and describes the biological species concept of reproductive isolation. It also covers the mechanisms of allopatric and sympatric speciation, examples of adaptive radiation, and models of punctuated equilibrium versus gradual evolution.

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PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 24
The Origin of Species

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Overview: The “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on Earth

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• Speciation, the origin of new species, is at the
focal point of evolutionary theory
• Evolutionary theory must explain how new species
originate and how populations evolve
• Microevolution consists of adaptations that evolve
within a population, confined to one gene pool
• Macroevolution refers to evolutionary change
above the species level

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The biological species concept emphasizes
reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance”

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The Biological Species Concept
• Members of a biological species are
reproductively compatible, at least potentially; they
cannot interbreed with other populations.

7. LE 24-3
Similarity between different species.
Diversity within a species.

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Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two
species from producing viable, fertile hybrids
• Two types of barriers: prezygotic and postzygotic

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• Prezygotic barriers impede mating or hinder
fertilization if mating does occur:
– Habitat isolation
– Temporal isolation
– Behavioral isolation
– Mechanical isolation
– Gametic isolation

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• Habitat isolation: Two species encounter each
other rarely, or not at all, because they occupy
different habitats, even though not isolated by
physical barriers

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• Temporal isolation: Species that breed at different
times of the day, different seasons, or different
years cannot mix their gametes

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• Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective
barriers

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• Mechanical isolation: Morphological differences
can prevent successful mating

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• Gametic isolation: Sperm of one species may not
be able to fertilize eggs of another species

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• Postzygotic barriers prevent the hybrid zygote
from developing into a viable, fertile adult:
– Reduced hybrid viability
– Reduced hybrid fertility
– Hybrid breakdown

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• Reduced hybrid viability: Genes of the different
parent species may interact and impair the
hybrid’s development

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• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile

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• Hybrid breakdown: Some first-generation hybrids
are fertile, but when they mate with another
species or with either parent species, offspring of
the next generation are feeble or sterile

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Limitations of the Biological Species Concept
• The biological species concept does not apply to
– Asexual organisms
– Fossils
– Organisms about which little is known
regarding their reproduction

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Other Definitions of Species
• Morphological: defines a species by structural
features
• Paleontological: focuses on morphologically
discrete species known only from the fossil record
• Ecological: views a species in terms of its
ecological niche
• Phylogenetic: defines a species as a set of
organisms with a unique genetic history

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Speciation can take place with or without
geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
– Sympatric speciation

30. LE 24-5
Allopatric speciation Sympatric speciation

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Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is interrupted or
reduced when a population is divided into
geographically isolated subpopulations
• One or both populations may undergo
evolutionary change during the period of
separation

32. LE 24-6
A. harrisi A. leucurus

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• To determine if allopatric speciation has occurred,
reproductive isolation must have been established

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Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place in
geographically overlapping populations

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Polyploidy
• Polyploidy is presence of extra sets of
chromosomes due to accidents during cell division
• It has caused the evolution of many plant species
• An autopolyploid is an individual with more than
two chromosome sets, derived from one species

36. LE 24-8
Failure of cell division
in a cell of a growing
diploid plant after
chromosome duplication
gives rise to a tetraploid
branch or other tissue.
Gametes produced
by flowers on this
tetraploid branch
are diploid.
Offspring with
tetraploid karyo-
types may be
viable and fertile—
a new biological
species.
2n = 6
4n = 12 4n
2n

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Habitat Differentiation and Sexual Selection
• Sympatric speciation can also result from the
appearance of new ecological niches
• In cichlid fish, sympatric speciation has resulted
from nonrandom mating due to sexual selection

38. LE 24-10
Normal light Monochromatic orange light
P. pundamilia
P. nyererei

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Allopatric and Sympatric Speciation: A Summary
• In allopatric speciation, a new species forms while
geographically isolated from its parent population
• In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species

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Adaptive Radiation
• Adaptive radiation is the evolution of diversely
adapted species from a common ancestor upon
introduction to new environmental opportunities

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• The Hawaiian archipelago is one of the world’s
great showcases of adaptive radiation

43. LE 24-12
KAUAI
5.1
million
years OAHU
3.7
million
years
HAWAII
0.4
million
years
1.3
million
years
MAUI
MOLOKAI
LANAI Argyroxiphium sandwicense
Dubautia linearis
Dubautia scabra
Dubautia waialealae
Dubautia laxa
N

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Studying the Genetics of Speciation
• The explosion of genomics is enabling
researchers to identify specific genes involved in
some cases of speciation

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The Tempo of Speciation
• The fossil record includes many episodes in which
new species appear suddenly in a geologic
stratum, persist essentially unchanged through
several strata, and then apparently disappear
• Niles Eldredge and Stephen Jay Gould coined the
term punctuated equilibrium to describe periods of
apparent stasis punctuated by sudden change
• The punctuated equilibrium model contrasts with a
model of gradual change in a species’ existence

46. LE 24-13
Time
Gradualism model Punctuated equilibrium model

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Macroevolutionary changes can accumulate
through many speciation events
• Macroevolutionary change is cumulative change
during thousands of small speciation episodes

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Evolutionary Novelties
• Most novel biological structures evolve in many
stages from previously existing structures

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• Some complex structures, such as the eye, have
had similar functions during all stages of their
evolution

50. LE 24-14
Complex camera-type eye
Pinhole camera-type eye Eye with primitive lens
Patch of pigmented cells Eyecup
Pigmented cells
(photoreceptors)
Epithelium
Nerve fibers
Fluid-filled cavity
Epithelium
Pigmented
layer (retina)
Optic
nerve
Pigmented
cells
Nerve fibers
CorneaCellular
fluid
(lens)
Optic nerve
Cornea
Lens
Optic nerve
Retina

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Evolution Is Not Goal Oriented
• The fossil record often shows apparent trends in
evolution that may arise because of adaptation to
a changing environment

52. LE 24-20
Pleistocene
Sinohippus
Recent
Pliocene
Anchitherium
Miocene
Paleotherium
Oligocene
Propalaeotherium
Eocene Pachynolophus
Hyracotherium
Mesohippus
Miohippus
Orohippus
Epihippus
Key
Grazers
Browsers
Hypohippus
Parahippus
Archaeohippus
Merychippus
Callippus
Megahippus
Pliohippus
Nannippus
Hipparion Neohipparion
Hippidion and other genera
Equus

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• According to the species selection model, trends
may result when species with certain
characteristics endure longer and speciate more
often than those with other characteristics
• The appearance of an evolutionary trend does not
imply that there is some intrinsic drive toward a
particular phenotype