Transcript Charles Darwin`s Theory of Evolution as a Mechanistic Process

CHARLES DARWIN: THEORY OF
EVOLUTION AS A MECHANISTIC PROCESS
JRMG
Bio1 2008
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
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
RADIATION
FINCHES
 ADAPTIVE
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
 Ex. Eastern and western meadowlark


Geographical isolation
Two populations are separated by geographic barriers
 Acted by natural selection
 Ex. Abert and Kaibab Squirrels

PROCESS OF SPECIATION
Behavioral
Geographical
PROCESS OF SPECIATION

Temporal isolation

Two or more species reproduce at the different times
DIANE DODD’S EXPERIMENT