Download Ch24 7th Ed

The Origin of Species
• Evolutionary theory
– Must explain how new species originate in
addition to how populations evolve
• Macroevolution
– Refers to evolutionary change above the
species level
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• Two basic patterns of evolutionary change can
be distinguished
– Anagenesis
– Cladogenesis
Figure 24.2 (a) Anagenesis
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(b) Cladogenesis
• The biological species
concept emphasizes
reproductive ??
• isolation
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Reproductive Isolation
– Is the existence of biological factors that
impede members of two species from
producing viable, fertile hybrids
– Is a combination of various reproductive
barriers
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• Prezygotic barriers ??
• Impede mating or fertilization of ova
• Postzygotic barriers ??
• prevent the hybrid zygote from developing into
a viable, fertile adult
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Limitations of the Biological Species Concept
• The biological species concept cannot be
applied to
– Asexual organisms
– Fossils
– Organisms about which little is known
regarding their reproduction
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• Speciation can occur in two ways
• 1. Allopatric speciation
• 2. Sympatric speciation
(a)
(b)
.
Figure 24.5 A, B
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• Once geographic separation has occurred
– One or both populations may undergo
evolutionary change during the period of
separation
A. harrisi
Figure 24.6
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A. leucurus
Adaptive Radiation
• Adaptive radiation
– Is the evolution of diversely adapted species
from a common ancestor upon introduction to
new environmental opportunities
Figure 24.11
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• The Hawaiian archipelago
– Is one of the world’s great showcases of
adaptive radiation
Dubautia laxa
1.3 million years
MOLOKA'I
KAUA'I
MAUI
5.1
million
years O'AHU LANAI
3.7
million
years
Argyroxiphium sandwicense
HAWAI'I
0.4
million
years
Dubautia waialealae
Figure 24.12
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Dubautia scabra
Dubautia linearis
• The punctuated equilibrium model
– Contrasts with a model of gradual change
throughout a species’ existence
Figure 24.13
Time
(a) Gradualism model. Species (b) Punctuated equilibrium
descended from a common
model. A new species
ancestor gradually diverge
changes most as it buds
more and more in their
from a parent species and
morphology as they acquire
then changes little for the
unique adaptations.
rest of its existence.
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• Some complex structures, such as the eye
– Have had similar functions during all stages of
their evolution
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Nerve fibers
(a) Patch of pigmented cells.
(b) Eyecup. The slit shell
The limpet Patella has a simple
mollusc Pleurotomaria
patch of photoreceptors.
has an eyecup. Cornea
Fluid-filled cavity Cellular
fluid
Epithelium (lens)
Optic
nerve
Pigmented
layer (retina)
Optic nerve
(d) Eye with primitive lens. The
(c) Pinhole camera-type eye.
The Nautilus eye functions Cornea
marine snail Murex has
like a pinhole camera
a primitive lens consisting of a mass of
(an early type of camera
crystal-like cells. The cornea is a
lacking a lens).
transparent region of epithelium
(outer skin) that protects the eye
Lens
and helps focus light.
Optic nerve
Figure 24.14 A–E
Retina
(e) Complex camera-type eye. The squid Loligo has a complex
eye whose features (cornea, lens, and retina), though similar to
those of vertebrate eyes, evolved independently.
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• Homeotic genes
– Determine such basic features as where a pair
of wings and a pair of legs will develop on a
bird or how a flower’s parts are arranged
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Evolution Is Not Goal Oriented
– Trends in evolution may arise because of adaptation to
a changing environment
– The appearance of a trend does not imply an intrinsic
drive toward a particular phenotype
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• The appearance of an evolutionary trend does
not imply an intrinsic drive toward a particular
phenotype
– In common?
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