Download Darwin`s Idea of Common Descent

Charles Darwin: Theory
of Evolution as a
Mechanistic Process
JRMGUCE
2009
Charles Darwin: Theory of Evolution
as a Mechanistic Process
•
•
•
•
Darwin’s Idea of Common Descent
Darwin’s Idea of Multiplication of Species
Darwin’s Idea of Gradualism
Darwin’s Idea of Natural Selection
Darwin’s Idea of Common Descent
•Descent with
modification
A.K.A EVOLUTION
• common ancestor/prototype
• Accumulated diverse
modifications or adaptations
The finches posed questions to Darwin:
Did they descend from one mainland
ancestor, did islands allow isolated
populations to evolve independently, and
could present-day species have resulted
from changes occurring in each isolated
population???
Darwin’s Idea of Common Descent
• Life history is like
a tree
• Common trunk: multiple
branching and rebranching
• Common ancestor in
each fork of branching
• lineage of common
descent
• Extinct species
TAXONOMY:
Tree of Life
Carolus Linnaeus
- Species are fixed
- Ordered the great
diversity of organisms
into “groups
subordinate to groups”
Kingdom
Phylum
Class
Order
Family
Genus
Genus
species
Reflected the genealogy of the
tree of life
Darwin’s Idea of
Multiplication of Species
• species either split into or bud off other
species
• geographical isolation of a founder species.
Founder effect. The frequency of the a allele is low in the initial population, but a small
subset, in which one individual is Aa, is removed from the large population and founds a
new population. The frequency of a is markedly higher in this new population, due to its
relatively high frequency in the founders
Darwin’s Idea of Multiplication of
Species
• different ecological niches provide
different ways of living
• different plants and animals come to fill
different niches with different shapes and
behaviors
Darwin’s Idea of Gradualism
• changes through the gradual change
of population rather than the
sudden production of new individuals
• species arise:
• Through gradual accumulation of
adaptations to a different environment
e.g. Darwin’s finches  ADAPTIVE
RADIATION
• Rapid evolution may arise:
•
•
•
•
Isolation of small population
Migration of small group in a new environment
Through mass extinction
Because of geological barriers
Darwin’s Idea of Natural
Selection
• Compared processes in nature with artificial selection
• Developed a scientific hypothesis to explain
how evolution occurs
• Struggle for existence (Malthus)
• Members of each species compete regularly
to obtain food and living space and other
necessities in life
• Central to his Theory of Evolution
Survival of the
Fittest
* key factor in the
struggle for existence
* Fitness
-ability to survive and
reproduce
-result of adaptation
-central to the process
of evolution by natural
selection
• LOW FITNESS
» Either DIE or LEAVE FEW OFFSPRINGS
• HIGH FITNESS LEVEL
– many OFFSPRINGS
• referred to as: NATURAL SELECTION
• accumulation of changes that differentiate
groups from one another, such that a new
species may arise
DARWIN’s MISSING
INGREDIENT
Darwin did not understand the genetic basis
for variation
– variations
–mutations
–genetic recombination
– mutation as a raw material for evolution
OTHER THINGS TO BE
CONSIDERED
• Natural vs. Artificial selection
• Importance of population in evolution
• smallest unit that can evolve
• Natural selection acts on individuals but
INDIVIDUALS DO NOT EVOLVE
Darwinian View of LIFE
• Diverse forms have arisen
– DESCENT WITH MODIFICATION FROM ANCESTRAL SPECIES
» Biological diversity
• Mechanism of modification
– NATURAL SELECTION
Patterns of Evolution
• Mass extinction
• 99% of the species ever lived are now extinct
• wiped out whole ecological systems*
• Cretaceous extinction
» Large asteroid struck the earth
• Can be caused by eruptions of many large
volcanoes (Permian and Cretaceous) , changing of
positions of continents and changing of sea levels
Patterns of Evolution
• Adaptive Radiation
•single species or small
group of species has
evolved into several
different forms that live
in different ways
•Ex. Darwin’s Finches
Dinosaurs
Mammals
Patterns of Evolution
• Convergent Evolution
• unrelated organisms come to resemble one another
• Natural selection may mold different body structures
» structures tend to function the same way and look
similar
• Analogous structures
» same look and function
» Different embryonic origin
Patterns of
Evolution
Coevolution
two species evolve in
response to the
changes in each other
over time
Ex. Fig trees and
wasps
Patterns of Evolution
• Developmental Genes
and Body Plans
• Hox genes
Process of Speciation
• Species
• group of organisms that can interbreed and
produce a fertile offspring
• Share a common gene pool
• As new species evolve populations become
reproductively isolated from each other
• Reproductive isolation
» Can be: Behavioral, Geographical and Temporal
Process of Speciation
• Behavioral isolation
• Capable of interbreeeding but has different
courtship rituals or behavior
• Geographical isolation
• Two populations are separated by geographic
barriers
• Acted by natural selection
• Ex. Abert and Kaibab Squirrels
Process of Speciation
Process of Speciation
DIANE DODD’s Experiment