Transcript Charles Darwin

Charles Darwin
• Wrote in 1859: “On the Origin of
Species by Means of Natural Selection”
Two main points:
1. Species were not created in their
present form, but evolved from
ancestral species. (Descent With
Modification)
2. Proposed a mechanism for
evolution: NATURAL SELECTION
Speciation
• The evolution of new species.
What are the two driving forces
behind speciation?
Species
• A group of populations whose
individuals have the potential
to interbreed and produce
fertile offspring in a natural
environment. (Ernst Mayr)
Liger
Result of male lion and female
tiger mating in captivity.
Offspring are infertile.
Tigon
Result of male tiger
and female lion
mating incaptivity.
Offspring are infertile.
Separated both
geographically and
ecologically.
The biological species concept is based on
interfertility rather than physical similarity
Ethnic Groups
Speciation in African Cichlids
Macroevolution vs. Microevolution?
Macroevolution
is above the
species level.
Microevolution
is at the species level.
Speciation can take place with
or without geographic barriers.
Geographic Isolation
• Induced when the ancestral
population becomes separated by
a geographical barrier.
• Example:
Grand Canyon ground squirrels
Geographic
Isolation
Kaibab
Squirrel
(left)
Abert
Squirrel
(right)
Reproductive Isolating
Mechanisms
Geographic Isolation
Has speciation occurred during
geographic isolation?
Allopatric Speciation
Reproductive Barriers
• Any mechanism that impedes
two species from producing
fertile and/or hybrid offspring.
Figure 24.3 Courtship ritual
as a behavioral barrier
between species
Blue-Footed
Boobies
in the
Galapagos Islands
Behavioral Isolation (Courtship Rituals)
Reproductive Isolating
Mechanisms
Sciurus carolinensis,
the gray squirrel,
breeds in July and August
Sciurus niger, the fox
squirrel breeds in May
and June
Temporal Isolation (a
specific type of
reproductive isolation)
Monterey Pine releases
pollen in early spring
Bishop’s Pine releases
pollen in summer
Reproductive Isolating Mechanism
• Behavioral Isolation
Bluestripe
butterflyfish
Ornate butterflyfish
Mechanical Isolation
Ensatina eschscholtzii, a ring species, here in the
Golden State, an example of
reduced hybrid viability and adaptive radiation
Ecological Isolation
White-throated Sparrow
feeds in dense thickets White-crowned Sparrow
inhabits fields and meadows
A Model for Adaptive Radiation on Island Chains
Hawaiian
Silversword
Evolved
5 million
years ago;
28 endemic
species
Adaptive Radiation
• Emergence of numerous species from a
common ancestor introduced to new and
diverse environments.
• Occurs as a result of Divergent
Evolution
• Examples:
Darwin’s Finches, African Cichlid Fish
Different geographic regions, different mammalian
“brands” – Eutherian vs. Marsupials
Convergent
Evolution
Gradualism
Punctuated Equilibrium
Interpretations of Speciation
• Two theories:
1. Gradualist Model:
Slow changes in species
overtime.
2. Punctuated Equilibrium:
Evolution occurs in spurts of
relatively rapid change.
(Eldredge and Gould)
Macroevolutionary changes can
accumulate through many
speciation events.
“Evo-Devo” biologists compare
developmental processes of
different multicellular organisms
Development is intimately connected
to evolution because all changes in
form come about through changes
in development.
Homeotic Genes – any of the master
regulatory genes that control
overall body plan of animals and
plants by controlling the
developmental fate of groups of
cells
The products of one class of
homeotic genes called Hox genes
provide positional information in
an animal embryo.
Hox mutations and the origin of
vertebrates
Homologous genes that affect pattern
formation in a fruit fly and a mouse
“The amazing diversity of organisms
has been produced by a modest
number of genes”
(Sean Carroll – author of Endless
Forms Most Beautiful)
The biggest difference between
amphibian eggs and reptilian eggs
was the development of the. . .
The five groups of vertebrates are:
Reptiles can reproduce in three
ways. These are:
Name two characteristics
common to almost all members
of the following classes of
animals:
• amphibians
•
reptiles
•
mammals
A phylogenetic tree can be used to
show . . ..
All mammals are classified into
these three groups:
Which two characteristics do all
chordates have?
Speciation that occurs in
which members are separated
from each other is
called ____________ speciation.
Speciation that occurs in
which members have no barriers
between them is called
______________ speciation.
1)Other than the example given
in the powerpoint presentation, give
an example of convergent evolution
among species.
2) What are the two theories regarding the pace of evolution?
Peter and Rosemary Grant are
famous for …
If two or more species reproduce at different times this is
called ____________ isolation.