1. Descent with Modification Part A: Darwin & Natural Selection
Chapter 19
Descent with Modification
Part A: Darwin & Natural Selection

2. What you must know:
Several examples of evidence for evolution from different scientific disciplines and how each supports change of populations over time.
The difference between structures that are homologous and those that are analogous, and how this relates to evolution.
The role of adaptations, variation, time, reproductive success, and heritability in evolution.

3. Descent with Modification
Theme:
Evolutionary change is based on the interactions between populations & their environment which results in adaptations (inherited characteristics) to increase fitness
Define: Evolution
Descent with modification (Darwin)
Change over time in the genetic composition of a population from generation to generation

4. Carolus Linnaeus = founder of taxonomy
binomial nomenclature: genus, species
Domain – Kingdom – Phylum – Class – Order – Family - Genus – Species
Dear King Philip Came Over For Good Spaghetti
Classification based on anatomy & morphology
Carolus Linnaeus

5. Slow & subtle changes in organisms  big change
Hutton: geologic change results from slow & gradual, continuous process
Lyell: Earth’s processes same rate in past & present  therefore Earth is very old
Slow & subtle changes in organisms  big change
James Hutton
Charles Lyell

6. Lamarck Published theory of evolution (1809)
Jean-Baptiste de Lamarck
Lamarck
Published theory of evolution (1809)
Use and Disuse: parts of body used  bigger, stronger (eg. giraffe’s neck)
Inheritance of Acquired Characteristics: modifications can be passed on
Importance: Recognized that species evolve, although explanation was flawed

7. Charles Darwin (1809-1882) English naturalist
1831: joined the HMS Beagle for a 5-year research voyage around the world
Collected and studied plant and animal specimens, bones, fossils
Notable stop: Galapagos Islands

8. Darwin waited 30 years before publishing 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”

9. Descent With Modification
Organisms descended from an ancestor that lived in the remote past
“I think …”
(Darwin’s sketch)

10. Darwin’s Overall Conclusions
Variation exists in every population which may have been inherited and the result of a mutation
Production of more individuals (overproduction of offspring) than can be supported by the environment leads to a struggle for existence among individuals
Only a fraction of offspring survive each generation
Survival of the Fittest
Adaptation: Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals
Called fitness
High survival = more offspring = more fit
Descent with Modification: Over time these adaptations will increase in the population.

11. Natural Selection
Adaptations enhance an organism’s ability to survive and reproduce in specific environments
Eg. Desert fox - large ears, arctic fox - small ears

12. Natural Selection
Artificial Selection
Nature decides
“Man” decides
Works on individual
Selective breeding
Inbreeding occurs
eg. beaks
eg. dalmations
Therefore, if humans can create substantial change over short time, nature can over long time.

13. Key Ideas of Natural Selection:
Competition for limited resources results in differential survival.
Evolutionary Fitness: Individuals with more favorable adaptations are more likely to survive and produce more offspring, and pass traits to future generations
If environment changes or individuals move to new environment, new adaptations and new species may arise.
Populations evolve, not individuals.

14. Recap main ideas of natural selection:
Evolution is change in species over time.
There is overproduction of offspring, which leads to competition for resources.
Heritable variations exist within a population.
These variations can result in differential reproductive success.
Over generations, this can result in changes in the genetic composition of the population.
Remember:
Individuals do NOT evolve! Populations evolve.

15. Evidence for Evolution:
Direct Observations
Homology
Fossil Record
Biogeography

16. Evidence for Evolution
1. Direct Observations
2. Homology
3. Fossil Record
4. Biogeography

17. Evidence for Evolution: 1. Direct Observations
Examples:
Insect populations become resistant to pesticides (DDT)
Antibiotic-resistant bacteria (MRSA)
Peppered moth (pollution in city vs. country)

18. The Rise of MRSA (methicillin-resistant Staphylococcus aureus)

19. Evidence for Evolution: 2. Homology
Homology: characteristics in related species can have underlying similarity even though functions may differ
Examples:
Homologous structures: similar anatomy from common ancestors (eg. forelimbs of human/cat/whale/bat)
Embryonic homologies: similar early development (eg. vertebrate embryos with tail & pharyngeal pouches)
Vestigial organs: structures w/little or no use (eg. flightless bird wings)
Molecular homologies: similar DNA and amino acid sequences

20. Homologous Structures

21. Embryonic Development

22. Vestigial Structures

23. Molecular Homologies
Compare DNA and amino acid sequences

24. Convergent Evolution
Distantly related species can resemble one another
Similar problem, similar solutions!
Analogous structures: similar structures, function in similar environments
Eg. Torpedo shape of shark, penguin, & dolphin

25. Evidence for Evolution: 3. Fossil Record
Fossils = remains or traces of organisms from past
Found in sedimentary rock
Paleontology: study of fossils
Show evolutionary changes that occur over time and origin of major new groups of organisms
Ankle bones

26. Prokaryotes (oldest fossils)  eukaryotes (fish – amphibians – reptiles – birds – mammals)
Transitional forms = links to modern species

27. Evolutionary Tree

28. Evidence for Evolution: 4. Biogeography
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
Eg. Marine iguanas in the Galapagos

29. Island Biogeography

30. Galapagos Tortoises

31. (evolutionary history)
Systematics: classifying organisms and determining their evolutionary relationships
Taxonomy
(classification)
Systematics
Phylogenetics
(evolutionary history)

32. Morphology (homologous structures)
Tools used to determine evolutionary relationships:
Fossils
Morphology (homologous structures)
Molecular evidence (DNA, amino acids)
Who is more closely related?
Animals and fungi are more closely related than either is to plants.

33. What kind of organism is this?
Legless conditions evolved separately  analogous structures evolved by convergent evolution
What kind of organism is this?

34. Taxonomy: classifying and naming organisms
Ordered division of organisms based on similar/different characteristics Dear King Philip Came Over For Good Spaghetti Each category at any level is called a taxon.

35. Binomial nomenclature (Genus species)
Naming system developed by Carolus Linnaeus

36. Phylogenetic Tree
Branching diagram that shows evolutionary history of a group of organisms

38. Branch lengths can represent genetic change

39. Branch lengths can indicate time

40. Constructing Phylogenetic Trees
Divergent vs. Convergent Evolution
Sorting homology from analogy

42. Cladogram: diagram that depicts patterns of shared characteristics among groups
Clade = group of species that includes an ancestral species + all descendents
Shared derived characteristics (evolutionary novelties) are used to construct cladograms
Turtle
Leopard
Hair
Amniotic egg
Four walking legs
Hinged jaws
Vertebral column
Salamander
Tuna
Lamprey
Lancelet (outgroup)
Cladogram
Shared ancestral characteristic (of all vertebrates) = vertebral column
Shared derived characteristic of mammals = hair

43. Constructing a phylogenetic tree
A 0 indicates a character is absent; a 1 indicates that a character is present.

44. Draw a phylogenetic tree based on the data below
Draw a phylogenetic tree based on the data below. Draw hatch marks on the tree to indicate the origin(s) of each of the 6 characters.

45. Answer:

46. Principle of maximum parsimony: use simplest explanation (fewest DNA changes) to construct phylogenetic tree – “keep it simple”
The first tree is the most parsimonious  fewest changes in bases

47. Molecular clock for mammals
Molecular clocks: measure evolutionary change based on regions of genome that appear to evolve at constant rates
Estimate date of past evolutionary events
Eg. Origin of HIV infection in humans= 1930’s
Molecular clock for mammals
Origin of HIV-1 M

48. 3 Domains: Bacteria, Archaea, Eukarya
Tree of Life
3 Domains: Bacteria, Archaea, Eukarya
Based on sequence data for rRNA and other genes

49. Common Ancestry of All Life Forms
Elements conserved across all 3 domains:
DNA and RNA are carriers of genetic info
Universal genetic code (codons  amino acids)
Conserved metabolic pathways

50. Conserved elements in Eukaryotes:
Cytoskeleton
Membrane-bound organelles
Linear chromosomes
Endomembrane systems (including nuclear envelope)

51. Horizontal Gene Transfer
Movement of genes between different domains
Exchange of transposable elements, plasmids, viral infections, fusion of organisms
Trees are complex!
Phylogenetic trees are hypotheses subject to change based on available data