Download Evolution

Evolutionary Biology: Introduction and History
Why learn evolutionary biology?
• Evolution is the unifying theory of biology
• “Nothing in biology makes sense except in the light of evolution” – Theodosius
Dobzhansky
Evolution
• Evolution = change
• Biological or organic evolution is the change in the properties of groups of
organisms over the course of generations
– Individuals do not evolve
– Populations evolve, undergoing “descent with modification”
Descent with modification
Before Darwin
Special creation - Each species had been individually created by God and do not
change
Scala Naturae
Harmony of Design
• ‘Perfect’ design of living things seen as proof of a creator
• William Paley, founder of Natural Theology (1800’s)
• The eye implies a Designer, as a watch implies a watchmaker
Harmony of Design
• A current movement: Intelligent Design
• Suggest that design is empirically recognizable based on probabilities for
complex events (eyes are ‘too complex’ to have resulted from ‘random events’)
Summary of Special Creation and Harmony of Design Premises
• Independent creation
• Species characteristics and species numbers do not change
• Complexity of organisms is proof of a designer
Premise: Independent Creation
• Evidence: Relatedness of life forms
Premise: Independent Creation
• Evidence: Relatedness of life forms
– Biogeography
– Phylogeny
The Tree of Life
Premise: Species fixed
• Evidence: observation of fossils
– Extinction
Premise: Species fixed
• Evidence: observation of transitional forms
– Example: transition from fish to amphibians
Premise: Species fixed
• Evidence: direct observation
– Soapberry bugs, Darwin’s finches
– Evolution of resistance, evolution of HIV
Premise: Perfect Design
• An elegant rebuttal by evolutionary biologist Richard Dawkins (1991)
Premise: Perfect Design
• Evidence: imperfect design!
– The blind spot in the human eye
Premise: Perfect Design
• Squid eyes are ‘designed’ better
Premise: Perfect Design
• Complex organs did not evolve instantly from nothing
• Arguments about probabilities (e.g. Intelligent Design) ignore transitional forms
Premise: Perfect Design
• Evidence: Vestigial structures
Premise: Perfect Design
• Evidence: Vestigial structures
Before Darwin
• Inheritance of acquired characteristics - Lamarck
Darwin’s Voyage
•In 1861, at age 22, Charles Darwin began a five-year, round-the-world voyage
aboard the Beagle as the ship’s naturalist
Voyage of the Beagle
Galapagos Islands
Malthus - Struggle to Survive
• Thomas Malthus, a clergyman and economist, wrote essay arguing that as
population size increases, resources dwindle, and conflict increases
Malthus and Darwin
•"In October 1838, that is, fifteen months after I had begun my systematic inquiry,
I happened to read for amusement Malthus on Population, and being well
prepared to appreciate the struggle for existence which everywhere goes on from
long- continued observation of the habits of animals and plants, it at once struck
me that under these circumstances favourable variations would tend to be
preserved, and unfavourable ones to be destroyed. The results of this would be
the formation of a new species. Here, then I had at last got a theory by which to
work". Charles Darwin, from his autobiography. (1876)
Alfred Wallace
•Naturalist who arrived at the same conclusions Darwin did
•Prompted Darwin to finally present his ideas in a formal paper
Darwin’s Descent with Modification
Transformational evolution vs. variational evolution
Testing Darwin’s theory: his 4 postulates
• Individuals within species vary
• Some variation is passed to offspring (heritable)
• More offspring are produced than can survive and/or reproduce
• Survival and reproduction is not random, but related to phenotypic variation
1. Variation in phenotype
• Arctic char morphology
2. Variation is heritable
• Head morphology differs in char raised in common environment
3 + 4 Variation in survival and reproduction related to phenotype
• Char variation affects feeding (which should affect survival)
One big problem
• How are traits passed to offspring?
• Darwin’s idea: Pangenesis (blending inheritance)
• Mendel’s research on particulate inheritance in peas (1865; rediscovered in
1900) was key in understanding evolution
The Modern Synthesis
• Fisher, Wright, and Haldane: combined Mendelian genetics with Darwin’s
theory of evolution by natural selection
The Modern Synthesis
• Read pages 10-11
• Random mutation and recombination leads to variation within populations
• Because mutation and recombination have small effects, populations evolve
via changes in allele frequencies due to natural selection, drift and gene flow
• Species are comprised of variable populations; speciation via reproductive
isolation
Evolution as Fact and Theory
• How is a theory defined in science?
• Evolution is a fact described by evolutionary theory!
Evolutionary questions about HIV
• Why have HIV treatments proven ineffective?
• Why are some people resistant to HIV?
• Where did HIV come from?
Life cycle of HIV
HIV
• Retrovirus – genetic information flows from RNA to DNA to mRNA to proteins
• Virus uses the host cell’s own enzymatic machinery
Progression of HIV infection
• In acute phase, HIV virions enter body and replicate rapidly, CD4 helper T cell
numbers fall
• Immune system slows down HIV’s replication and CD4 recovers slightly
• Replication continues to rise and CD4 cells fall until onset of AIDS
How AZT works
AZT Resistance
AZT Resistance
Change in transcriptase structure due to high mutation rate in HIV
Evolution of resistance
Evolutionary pattern in patients
Drug cocktails
• Use of drug cocktails in HIV treatment has been effective to keep changing the
selective force
Evolutionary relationships