Download 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.
Species
• A group of populations whose
individuals have the potential
to interbreed and produce
fertile offspring in a natural
environment. (Ernst Mayr)
The biological species concept is based on
interfertility rather than physical similarity
Ethnic Groups
Macroevolution vs. Microevolution?
Macroevolution
is above the
species level.
Microevolution
is at the species level.
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)
Harris’ Antelope Squirrel (left) /Whitetailed Squirrel (right)
Premating Isolating Mechanism:
Geographical Isolation
 The Grand Canyon is a geographical
barrier that can promote speciation.
 The Kaibab squirrel (left) lives on the
North Rim while the Abert squirrel
(right) lives on the South Rim.
Has speciation occurred during
geographic isolation?
Reproductive Barriers
• Any mechanism that impedes
two species from producing
fertile and/or hybrid offspring.
Reproductive Isolating
Mechanisms
Geographic Isolation
Reproductive Isolation
• Result of a radical change in the
genome that produces a
reproductively isolated sub-population
within the parent population (rare).
• Example: Wood Frogs and Pickerel
Frogs live in the same communities
but mate weeks apart and have
different mating calls
Temporal Isolation (a
specific type of
reproductive isolation)
Monterey Pine releases
pollen in early spring
Bishop’s Pine releases
pollen in summer
Reproductive Isolating
Mechanisms
Sciurus carolinensis,
the gray squirrel,
breeds in July and August
Sciurus niger, the fox
squirrel breeds in May
and June
Reproductive Isolating Mechanism
• Behavioral Isolation
Bluestripe
butterflyfish
Ornate butterflyfish
Figure 24.3 Courtship ritual
as a behavioral barrier
between species
Blue-Footed
Boobies
in the
Galapagos Islands
Ecological Isolation
White-throated Sparrow
feeds in dense thickets White-crowned Sparrow
inhabits fields and meadows
Adaptive Radiation
• Emergence of numerous species
from a common ancestor introduced
to new and diverse environments.
• Occurs as a result of Divergent
Evolution
• Example:
Darwin’s Finches
Ensatina eschscholtzii, a ring species,
here in the Golden State
A model for adaptive radiation on island
chains
Different geographic regions, different mammalian
“brands” – Eutherian vs. Marsupials
Convergent
Evolution
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)
Gradualism
Punctuated Equilibrium
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.
“Evo-Devo” biologists compare
developmental processes of
different multicellular organisms
“The amazing diversity of organisms
has been produced by a modest
number of genes”
(Sean Carroll – University of Wisconsin)
(Go Badgers!)
Hox mutations and the origin of vertebrates