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Chapter 22
Darwinian Evolution
What is evolution ?
Descent with Modification
evolutionary change is based on the interactions
between populations & their environment
which results in adaptations (inherited
characteristics) to increase fitness
Evolution
change over time in the genetic composition of
a population.
Historical Context of Evolution
Darwin was influenced by many scientists in
developing his theory.
•Species are fixed (unchanging)
•Life-forms arranged of scale
(ladder) of increasing complexity
(scala naturae)
•Each life form had its permanent
place on the ladder
Aristotle
384-322 B.C
•Follows Old Testament
(creationism)
Carolus Linnaeus
1707-1778
•Founder of taxonomy/binomial
nomenclature
Domain – Kingdom – Phylum – Class –
Order – Family - Genus – Species
•Domains: Eubacteria, Archaea, Eukarya
•Nested system: species grouped into
increasingly general categories
•Classification based on anatomy &
morphology
Classified diversity for the
“greater glory of God”
•Grouped species by resemblances from
pattern of their creation not evolutionary
relationships
George Cuvier
(1769-1832)
Paleontologist – studied fossils
•Deeper strata (layers) - very
different fossils from current life
•Extinctions were common
occurrences yet opposed idea of
evolution
Catastrophism : events
destroyed many living species in
local areas, then area was
repopulated by immigrant
species
Geology
James Hutton
1726-1797
• Gradualism:
geologic change
results from slow,
gradual, continuous
process still
operating today.
Charles Lyell
1797-1875
• Gradualism
• Uniformitarianismm
echanisms of
change are slow and
constant over time.
• Slow & subtle
changes in
organisms lead to
big change
Jean Lamarck (1744-1829)
1801
1. Theory of desire
- organisms change due to inborn desire to change to
become more fit for environment
ex: ant eaters develop long snouts
2. Theory of use and disuse
- organs that are being used get large and strong
- organs that are not used shrink and eventually disappear
ex: snakes- didn’t use legs so disappeared
3. Theory of inheritance
- acquired traits were passed on to offspring
ex: snakes that lost legs passed trait
Importance: Recognized that species evolve, although explanation was flawed
Malthusian Doctrine
•More babies born than
deaths
•Consequences of
overproducing within
environment: war,
famine, disease
•Struggle for existence
Thomas Malthus
(1766-1834)
Charles Darwin (1809-1882)
•British naturalist
•Proposed the idea of
evolution by natural
selection
•Collected clear evidence
to support his ideas
Unique species
Darwin’s Finches
•Beak variation: an example of adaptive radiation.
•14 species of finches: evolved from one common
ancestor in South America
Darwin’s conclusions
• small populations of original South American
finches reached islands
• variation in beaks enabled some to obtain food
successfully in the different environments
• over many generations, the populations of finches
changed anatomically & behaviorally
• accumulation of advantageous traits
• emergence of different species
•Finches with beak
differences that allowed
them to…
- successfully compete
- successfully feed
- successfully reproduce
Other examples of adaptations to food source
1859: Origin of the Species
•Darwin waited 30 years before he
published his ideas on evolution
•Alfred Russell Wallace – published
paper on natural selection first
(1858)
•Charles Darwin (1859): On the
Origin of Species by Means of
Natural Selection
Mechanism for evolution is Natural
Selection
Darwin didn’t use “evolution”, but
rather “descent with modification”
Origin of the Species
Darwin amassed evidence that descent with modification
by natural selection explains three broad observations
about nature:
• The unity of life: organisms share many characteristics
• The diversity of life: organisms accumulate adaptations
• The match between organisms and their environments
Darwin’s Theory of Natural Selection
Natural selection
Individuals that have physical or behavioral traits that
better suit their environment are more likely to survive
and will reproduce more successfully than those
without traits.
Parts of Theory
1. Overproduction
- organisms produce more offspring than can survive
- leads to competition
2. Genetic variation
- individuals in a given species vary by chance
(due to gene recombination) - normal
.
exception: identical twins
3. Struggle to survive
- all organisms face constant struggle to survive
(limited resources)
4. Survival of the fittest
- Individuals best adapted to environment are more
likely to survive and reproduce
- Over time favorable traits increase in population
Adaptations enhance
an organism’s ability
to survive and reproduce.
Over long periods of time, steady input
of new variations in a population
lead to speciation.
DIFFERENCE IN THEORIES
Lamarck: organisms change in order to survive in
environment
- occurs in the organism’s lifetime
Darwin: environment determines which organisms
survive through natural selection
- occurs over many generations
Evidences of Evolution
1. Direct Observations
2. Fossil record
3. Homology
homologous & vestigial structures
embryology
molecular: protein & DNA sequence
4. Biogeograpy
1. Direct Observations
Antibiotic Resistance: MRSA
(methicillin-resistant Staphylococcus aureus)
Soapberry bug beak length shortened in response to
change in food source.
2. Fossil record
•
Most occur in layers of
rock, with the youngest
usually on top, and the
oldest in deeper layers
(sedimentary rock)
•
Some found in amber
(fossilized tree sap)
•
Record incomplete due to
soft outer coverings on
organisms not leaving
imprints
•
99% of all species that
lived on Earth are now
extinct.
Transitional Species (links to modern species)
Tiktaalik roseae, a 375 million-year-old transitional
species between fish and the first legged animals,
reveals that the evolution of hind legs actually began
as enhanced hind fins.
3. Homology
(similarities among organisms)
Homologous structures: structures which developed from a
common ancestor, but have changed over time due to
different purposes (divergent evolution)
Embryologic similarities
•
evidence of a common
ancestor
•
dorsal, hollow nerve cord,
notochord (stiffening rod of
cartilage) in the back
•
similar membranes in the
embryos, yolk sac that
produces the first blood cells
and germ cells
•
similar development of
many organs
Vestigial organs/ structures:
•
Structures which have lost all or most of their
original function in a species through evolution.
•
Degenerated, atrophied, or rudimentary condition
•
Evidence of change over time
vestiges of pelvic girdle of
leg bones of walking ancestors
eyes on
blind cave fish
nicitating membrane
Molecular/ Biochemical homologies
•
DNA, RNA, amino acids, and serology (comparison of
blood chemistry)
Species
Gorilla
Rhesus monkey
Amino Acid
Differences
from Human
Hemoglobin
Protein
1
8
Mouse
27
Chicken
45
Frog
67
Lamprey
125
Evolutionary Trees
•Closely related species (branches)
share same line of descent until their
divergence from a common ancestor
•Homologous characteristics
that are inherited from a
common ancestor are strong
indications of evolutionary
relationships
•For example, "Tetrapods" all
possess four limbs, presumably
because they evolved from an
ancestor (#2) that had four
limbs.
Pg 464
Convergent evolution
•
•
independent evolution of similar features in different lineages
Distantly reated species resemble one another
Analogous structures: similar in appearance and function, but
different origins with different internal structures
- organisms with different ancestors become more alike
because they share same environment
dissimilar structures  more similar structures
4. Biogeography
• Geographic distribution of a species
• Species in nearby geographic areas resemble each other
- Continental drift and Pangaea explains
similarities on different continents
- Endemic species: found at a certain geographic
location and nowhere else
ex: Marine iguanas in the Galapagos
Island Biogeography
Natural Selection vs Artificial Selection
Natural Selection
Artificial Selection
Nature selects/decides
Man selects/decides
Acts on individual
Selective breeding
Population evolves over time
Inbreeding occurs
Occurs over long periods of time
Occurs in short period of time