Download biological evolution

Addition to the Syllabus
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CHAPTER 2:
BIOLOGICAL EVOLUTION
Evidence for Evolution
Evidence for evolution
•Evolution: a phenomenon resulting from the interplay of evolutionary
processes and evolutionary patterns.
•Evolutionary processes: innovative forces (natural selection, genetic drift).
•Evolutionary patterns: constraints (inheritance).
•Evolution implies genealogical links.
•Paradoxically, stable characters combined with change provide the best
evidence for evolution.
•Major sources of evidence:
•Molecular genetics.
•Embryology.
•Anatomy.
•Biogeography.
•Paleontology.
•Contemporary evidence.
Molecular genetics: gene expression
Protein
Translation
Cell cytoplasm
mRNA
Splicing
hnRNA
Cell nucleus
Transcription
DNA
Replication
DNA: deoxyribonucleic acid
hnRNA: heterogeneous nuclear ribonucleic acid
mRNA: messenger ribonucleic acid
Molecular genetics: DNA
Bases
(the sequence of bases carries
information needed to make
proteins in the cell’s cytoplasm)
Molecular genetics: genetic code
Amino acids:
Phe: phenylalanine
Leu: leucine
Ser: serine
Etc.
Amino acids are the
building blocks of
proteins.
There are twentysomething amino
acids in nature,
coding for a very large
number of proteins.
The genetic code is common to all animals
(and, in fact, with minor variations, to all life).
Molecular genetics: building phylogenetic trees based on molecular data
Candida
Saccharomyces
Neurospora
Moth
Screw worm
Tuna
Snake
Turtle
Penguin
Chicken
Duck
Pigeon
Kangaroo
Rabbit
Pig
Donkey
Horse
Dog
Monkey
Man
0
5
10
15
20
25
30
Average Minimal Mutation Distance
This tree is based on the sequence of amino acids in a protein
known as cytochrome-c, involved in oxygen transport.
Embryology: phylotypic stages
I
II
III
Fish Salamander Tortoise
Chick
Hog
Calf
Rabbit
Human
Phylotypic stage: a developmental stage common across species of the same phylum.
Anatomy
Human
Lizard Cat
Humerus
Whale
Bat Frog Bird
5
4
1
1
1
Ulna
1
2
54 3
Radius
Carpal
1
54
32
3
1 2
2
5
54 3
5
2
1
2
3
4
3
2
4
3
Homology of arm structure in tetrapod vertebrates: size and shape of these bones
vary, but their relative positions remain constant. Different functions are achieved
with the same bone structure.
Biogeography
Glyptodont
(fossil)
Armadillo
(living)
Local faunas: species are not randomly distributed in continental masses and
islands. Rather, similar animal species tend to be confined to the same areas.
Paleontology
Fossils: extinct species appear orderly across geological periods.
Paleontology
Wings
Teeth
Feathers
Bony tail
Transitional forms: Archaeopteryx litographica is an extinct
species with a mixture of avian and reptilian characters.
Contemporary evidence: Inclusive fitness
Natural selection
A female
opossum with
offspring
Direct fitness  offspring
Indirect fitness  relatives
A group of
female lions
(sisters)
Reciprocity  “friends”
A coalition of
male baboons
A female
opossum with
offspring
Direct fitness  offspring
Contemporary evidence: Adaptation by natural selection
Video
Contemporary evidence: Real-life examples
European conquest of the Americas
Evolution of antibiotic-resistant strains
Logic of natural selection
Natural selection will occur when these conditions are met by a
population of living organisms:
• Phenotypic variation
• Differential reproductive success
• Inheritance
Logic of natural selection
Generation 1,
infants
Generation 1,
reproductive age
Variability in
developmental
programs
Differential
death before
reproduction
Generation 2,
infants
Spread of
successful
variants
through
inheritance
Insipient speciation in nature: California salamanders
http://www.youtube.com/watch?v=GIGXLNYV9kc&feature=related
Video
David Wake: Insipient speciation in California salamanders
• Salamanders of northern California are genetically and phenotypically
variable.
• Over the last 10M years these salamanders have been moving south.
• One line migrated along the Sierra Nevada mountains.
• These salamanders evolved cryptic coloration (camouflage).
• A second line migrated along the coastal mountains.
• These salamanders evolved bright coloration (Mullerian mimicry).
• Hybrids found in southern California are neither cryptic nor bright, thus lacking
the benefits conferred by extreme phenotypes.
Natural selection and phenotypic change
(b) Directional
Frequency of Phenotypes
(a) Stabilizing
(c) Disruptive
25
25
25
20
20
20
15
15
15
10
10
10
5
5
5
0
0
0
0
2
4
-16
1
8
3
5
7
-1
9
1
3
5
7
9
Measuring natural selection in wild populations: Lions
Males
Females
0.08
Monthly Reproductive Rate
Reproductive Success
4
3
2
1
0
0.06
0.04
0.02
0.00
0
1
2
3
4
Coallition Size
5
6
0
5
10
Pride Size
15
Evolutionary processes
•Natural selection: differential reproductive success of
alternative traits.
•Correlation of characters: a trait that evolves because it is
genetically associated to a selected trait, rather than because
of direct positive selection.
•Genetic drift: random (nonselective) change in allele frequency
in a population.
•Mutation: random alterations in the sequence of bases in the
DNA molecule produced by copying errors, radiation,
chemicals, etc.
•Sexual reproduction: maintenance of genetic variability due to
the independent assortment of alleles from both parents.
Contemporary evidence
Video
Paul Ewald: Can we domesticate germs? (17:51 min)
http://www.ted.com/index.php/talks/paul_ewald_asks_can_we_domesticate_germs.html
Paul Ewald: Can we domesticate germs?
Cholera bacteria
•Why are some disease organisms more harmful than others?
•How can we make harmful organisms evolve toward benignness?
•Germ’s eye view: disease organisms have to get from one host to
another.
•Harmful: do not require host mobility (e.g., dispersed by water).
•Benign: require host mobility (e.g., person-to-person contact).
•Blocking water transmission could force harmful organisms to evolve
more benign forms.
•Coevolution of virulence and antibiotic resistance.