Evolution change over time

1
Evolution change over time

• Populations evolve not individuals
• Adaptations
• Inherited traits that enhance survival and thus
  reproduction in a particular environment
• Charles Darwin
• Theory of Evolution
• Based on many observations

2
Path to Darwins Theory

• Similar idea simpler forms of life preceded more
  complex forms from ancient Greeks (2500 years
  ago)
• Aristotle believed that species are fixed
• Judeo-Christian thought (book of genesis)
• Divine creator earth to be 6,000 years old
• Early fossil studies extinct spp. earth may be
  older
• Lamarck inheritance of acquired characteristics
• Lyell Geologist gradual change by nat. forces
• Darwins voyage

500 BC
322 BC
2000 yrs old
1700s
1809
1830
1831-1836
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• Charles Darwin British naturalist born 1809
• expanded on some existing ideas
• Geologists, naturalists, and scientists
• Did not address origin of life, but rather
  focused on explaining the vast diversity of life
• provided supportive evidence 5 year voyage
  around the world 1831-1836
• Galapagos Islands
• Wrote essay on evolution based on his
  observations/experiences 1844
• Published On the Origin of Species 1859 under
  competition by Wallace
• Descent with modification ancestral species
  could diversify into many descendent species by
  accumulation of adaptations to environment
• Hypothesized natural selection as driving force

4
What is natural selection?

• Over production of offspring
• Limited natural resources
• Heritable variations
• Differential or unequal reproductive success
• Offspring w/in a varied population, whose
  characteristics best adapt them to the
  environment are most likely to survive and
  reproduce
• more fit individuals leave more offspring than
  less fit individuals

5

• with so much diversity in just a few thousand
  years

6

• even more diversity over thousands of generations
• With natural selection over vast time allows for
  changes to accumulate

7
Evidence for evolution

• Fossils preservation of dead organic matter
• examples

35 mya
1.5 mya
375 mya
190 mya
40 mya
5,500 ya
8
Fossil record

• Layers of sediments
• Deposits pile up over millions of years forming
  strata
• Young on top older on bottom
• Read the layers
• compare preserved fossils
• track changes over time

9
Is Earth 6,000 years old or 4.6 billion?

• Radiometric Dating
• Dating geologic structures
• by rate of radioactive decay
• Atomic elements decay at a fixed rate
• Half-life time it takes for half of an element
  to decay
• C14 or radiocarbon dating (plants and animals)
• unstable carbon isotope, 5730 years to decay half
  of a sample
• C14 C12 ratio is half in fossil than atm 5730
• If C14 C12 ratio is ¼ of atm 11,460
• K40 has half life of 1.3 billion years
• Famous tests
• Iceman (Italy, 1991) dated to 5500 years old
• Shroud of Turin evidence shows to be about 700
  years old rather than 2000 years old

Dr. Willard Libby Atomic physicist Nobel
Prize for C14 dating work. Before that, was a
key researcher in the development of the atomic
bomb.
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Comparative anatomy embryology

• Homology
• Similarities in form and structure from common
  ancestory
• E.g. mammal forelimbs with different functions
• Similar embryological stages
• Common structures during similar early
  development (e.g., gill slits)

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Molecular Biology

• Hereditary background and proteins encoded in DNA
• Compare gene sequences
• Similar sequences more recent ancestor
• More dissimilar more distant ancestor

12
Why is evolution the best explanation to the vast
natural diversity?

• Mountains of evidence of various types
• e.g. fossils, radiometric dating, comparative
  anatomy embryology, molecular biology
• each agrees with the other
• provides tremendous support of evolution theory
• disagreement would be falsifiable evidence
• Theory still challenged
• Theory ? guess or based on any belief
• Theory falsifiable idea supported by extensive
  evidence
• Theory of Gravitation, Theory of
  Relativityprinciples based on facts (e.g. earth
  is round)

13
Populations evolve

• Although natural selection acts on individuals,
  which affects survival chances to reproduce
  w/in an env., a population changes over time

• Population genetics
• Darwins and Mendels ideas together
• Populations change genetically over time
• Gene pool
• All alleles in a population
• Microevolution
• Change in allele frequencies over time
• e.g. pesticide resistant allele will increase
  while its alternate decreases frequency

14
Agents of potential changes in allele frequency

• Natural Selection pesticide example
• Non-random mating
• Plants closer to each other may get fertilized
• People sometimes choose similar mates (short
  couples)
• Mutation - creates new alleles
• Gene flow gain or loss of alleles in a popln.
• Immigration or emmigration
• Genetic drift change in gene pool due to chance
• Founder effect colonization of small group
• Bottleneck effect reduction of population

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Genetic drift bottleneck effect

• Drastic reduction of popln. size
• Earthquakes, floods, fires, etc
• Surviving popln has underrepresented alleles

e.g. elephant seals were hunted down to
20 restored now to 30k found only 1 allele in
ea. of 24 genes no variation
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Selection pressures

• A particular phenotype selected for or against
  depending on the environment
• Guppy example
• 2 forces of natural selection working against
  each other mate preference and predator
  vulnerability
• Balance where females are attracted to males with
  brighter colored tails risk of attracting
  predators
• How could you test these selection pressures?

?
?
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• Observe many generations
• In predator-free environment?
• More brightly colored males with large tails
  evolved
• Re-introduced predators
• Less flashy males became more fit

18
Natural selection affects populations

• Affects the distribution of phenotypes
• Normal distribution of varied fur frequencies
• Stabilizing selection
• Reduces extremes favors intermediates
• Most common

19

• Directional selection
• Acting against one extreme or environment favors
  one extreme
• e.g. darker landscape or, insects exposed to
  pesticides

20

• Disruptive selection
• Environment is varied to favor both extremes
• e.g. patchy landscape with light soil and dark
  rocks