Evolution and Natural Selection

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Evolution and Natural Selection
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Evolution
Nothing in biology makes sense except in the
light of evolution Theodosius Dobzhansky
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Evolution
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Evolution

• Evolvere
• to unfold or unroll
• Central organizing concept of how the world and
  organism have come to function
• Builds on accumulating knowledge
• Need organisms history to fully understand it
• Descent with modification
• Often with diversification

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Evolution

• Genetic change in a population or species over
  generations heritable changes that have produced
  Earths diversity of organisms

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Before there was Darwin
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Anaximander

• 16th Cent BC

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Living creatures formed from water
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Humans and animals descended from fish
Interpreted observations of Sharks/dogfish as
intermediaries between fish and land animals
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History of Evolutionary thought
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Plato 427-347 BC

• Essentialism
• Essence- perfect form
• Earthly plane essential plane
• Static world
• Variation
• Imperfect earthly representation
• Only essence matters

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Aristotle 384- 322 B.C
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Aristotle 384- 322 B.C

• Essentialism with taxonomical organization
• Scala Naturae
• Aka Scale of nature
• Aka ladder of nature
• God created all species
• No gradation among species
• No new species, no extinctions
• Spontaneous generation

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Scala Naturae
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.Add Judeo-christianity
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Historical Time Frame

• Plato/ Aristotle
• Essentialism- fixed species
• Victorian era- 1700-1800
• Pre- science
• Natural Theology- Lifes diversity attributed to
  gods splendor
• God created all diversity
• Earth very young
• Role of science to catalogue gods creatures
• gods splendor in the intricacies of life
• Taxonomy

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Victorian Era

• Victorian era
• Conservative, chaste
• Lack in education
• Lack in communication
• Christianity dominated
• Earth created in 7 days
• Earth is not old 6000 yrs
• Earth is static

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Newton 1643- 1727

• Explained physical phenomena
• Introduced Mechanistic ideology
• Explain the world outside of god
• Introduced the power of reason
• Beginnings of an atmosphere that encouraged the
  questioning of old beliefs
• Spurred the Age of Enlightenment
• Faith in progress the power of reason

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Cuvier 1769-1832

• Paleontology, geology, comparative anatomy
• History of life documented via fossils
• Older fossils deeper
• Unique species at each depth
• Extinction via catastrophism
• Form function
• No evolution
• So complex could not be altered

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James Hutton 1726-1797

• Father of Geology
• Earth is OLD
• no vestige of a beginning, no prospect of an
  end
• Older than 6000 yrs
• Processes of earths changes can be explained by
  present time processes
• Ex water
• Gradualism
• Profound change is the cumulative product of slow
  continuous processes

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Charles Lyell

• Geologist
• Principles of Geology
• Earth is very old
• Uniformitarianism
• Geological processes have not changed over time-
  same rate today as in past
• Responsible for timeline of earth

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Thomas Malthus 1776- 1834

• Economist, Population study
• Essays on the principle of population 1798
• Populations grow faster than food supply
• Not all survive.struggle for life

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Jean Baptiste Lamarck

• First to propose Evolution
• Proposed idea adaptation
• Inheritance of acquired characteristics
• Introduced mechanism of evolution
• Use and disuse
• Incorrect mechanism
• Ridiculed

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Evolution was in the air

• Mechanistic thinking (Newton)
• Timeline- earth old (Hutton Lyell)
• Fossil evidence (Cuvier)
• Relatedness amongst species- descent via
  inheritance of characteristics over time (Lamark,
  buffon)
• Adaptation to environment (Lamark)
• Struggle for existence (Malthus)
• BUT natural theology is still prevalent

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Darwin
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Voyage of the Beagle, 1831
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Similar Solutions

• Adaptation
• Trait that aids in the survival or reproduction
  of an organism

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Fossils
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Galapagos
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Darwin

• Perspective
• Time to read
• Specimens survive

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Artificial Selection

• Intentional breeding for certain traits

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Darwins Observations

• Diversity
• Similar solutions- ie adaptations
• Fossils
• Geographic distribution
• Environment influences distribution of plants
  animals
• Read incorporated the work of others
• Malthus- population
• Lyell- earth old
• Artificial selection

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Darwin

• The origin of species
• on the origin of species by means of natural
  selection, or the preservation of favored races
  in the struggle for life
• Descent with modification
• Theory of natural selection

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Wallace 1823-1913

• Naturalist
• Father of Biogeography
• on the tendency of varieties to depart
  indefinitely from the original type
• Independently conceived natural selection
• Not so lucky

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Origin of Species

• Descent with modification
• Aka evolution
• All organisms related through descent from some
  unknown ancestor
• Happened over long periods of time
• Adapt to environment
• Well accepted within 15 years- timing
• Differential reproductive success
• More offspring than can survive will be produced
• Struggle to survive
• Variation among individuals
• Best suited for the environment will survive
• Aka Natural selection

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What was Darwin Missing?

• Mechanism of inheritance
• Hershey Chase 1952
• Linked DNA to inheritance
• Direct evidence for natural selection
• Grant Grant 1972-2003
• Darwins finches in Galapagos

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MUST Have for Natural Selection to occur

• Individual variation must exist
• Variation must be heritable
• Limited resource- selective pressure

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Evolution.After Darwin
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Evidence of Evolution

• Fossil record
• Biogeography
• Comparative anatomy
• Comparative embryology/ development
• Comparative behavior
• Molecular biology

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Fossils

• Fossil any preserved remnant or impression of an
  organism that lived in the past

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Biogeography

• Study of geographic distribution
• Use to study how lineages of animals evolved

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Comparative Anatomy

• Comparison of body structures among taxa to
  understand evolutionary relationships/ history
• Homologous vs analogous

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Homologous Structures

• A characteristic shared by 2 or more taxa that
  evolved from the same structure in their common
  ancestor

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Analogous Structures

• Analogous structures have a similar function but
  DO NOT share common ancestry

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Comparative Embryology

• Compare developmental patterns (ontology) to
  understand common ancestry

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Comparative Behavior

• Compare behavior to understand common ancestry

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Molecular biology

• Study of DNA sequences to understand evolutionary
  relationships
• Revolutionized our understanding of evolutionary
  biology

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Modern Synthesis

• Modern view of our understanding of evolution
• A comprehensive theory of evolution emphasizing
  natural selection, gradualism, and populations as
  the fundamental units of evolutionary change
• New Terms
• Evolution slow accumulation of change over time
• Mechanism of change natural selection
• Editing
• Evolutionary adaptation

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Natural Selection

• Differential success in the reproduction of
  different phenotypes resulting from the
  interaction of organisms with their environment
• Aka Reproductive advantage

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• Survival of the Fittest.

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Fitness

• Fitness
• Trait that results in increased reproductive
  success
• Darwinian fitness
• The contribution an individual makes to the gene
  pool
• Relative fitness
• Relative proportion of a genotype in the
  population

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Fitness
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Natural selection results in populations that are
better adapted To their parents environment
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Guppies, A story of Sex evolution
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David Reznick
Trinidad some time in the 1980s
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The Players
Pike Cichlid
Killfish
Guppies
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The Experiment
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MUST Have for Natural Selection to occur

• Individual variation must exist
• Variation must be heritable
• Limited resource- selective pressure

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Variation Exists in Life
Give Me an Example
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Variation must exist in a population

• Population group of individuals of the same
  species living in the same area at the same time

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Variation is Heritable

• DNA stores genetic information
• Instructions for all life and life processes
• Dna strands made up of Genes
• DNA is passed on from parents to offspring

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Chromosomes Are strands of DNA
Autosomal Chromosomes
Sex Chromosomes
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Terminology

• Gene
• Sequence of nucleotides that is the unit of
  hereditary information
• Ie. A recipe
• Genome
• The sum of an individuals genes
• Gene pool
• Genetic composition of a population aka all
  alleles in a population at a given time

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Genes Located on Chromosomes
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Terminology

• Genotype
• An organisms genetic makeup is the sequence of
  nucleotide bases in DNA, the gene
• Phenotype
• The phenotype is the organisms specific traits-
  how genes are expressed
• Physical manifestation of the characteristic

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Genotype vs Phenotype
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Selective Pressure

• Competition for a limiting resource
• Darwinmore offspring produced than can survive
• What are some limiting resources.
• Different types of selective pressures can lead
  to different patterns in natural selection

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Mechanisms of Natural Selection
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Natural SelectionHow Does it Happen?

• Directional selection
• 1 extreme is favorable
• Shifts phenotype of original population
• Stabilizing selection
• Intermediate favored
• Reduces variation in a population
• Diversifying selection
• 2 extremes favorable
• Can result in speciation

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Evolutionary Scale

• Microevolution
• Macroevolution

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Microevolution

• A change in the gene pool of a population from
  generation to generation
• Population genetics
• The study of genetic changes in populations over
  time
• Quantify molecular differences within and among
  populations
• Traits exhibit variation
• Traits we have identified genes for

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Population Genetics
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• Remember that changes in genes means changes in
  phenotype ratios

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Macroevolution

• Evolutionary change on a grand scale, includes
  the origin of new taxonomic groups, adaptive
  radiation, and mass extinction
• Hard to see in one life time

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Disruptive Selection
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Speciation

• The origin of new species in evolution
• Speciation is the process of forming new species
• While many take place slowly over generations
• some events can be observed in our life times
• Species biological species concept
• Members of a group of populations that interbreed
  or potentially interbreed with each other, under
  natural conditions, and produce viable offspring

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Antelope squirrels of the Grand canyon rim
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Adaptation

• A feature or characteristic that increases
  reproductive success (including survival)
• Increases fitness relative to an alternate trait

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Are all characteristics adaptations?

• Adaptationist Programme
• The position that a trait has been selected for
  adaptive value
• Ex. The case of female orgasm
• Non-adaptive traits
• The position that a trait was not selected for
  increased fitness
• Ex ontogenetic leftover that does not influence
  fitness

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Other forces that may drive evolution

• Mutation
• Change in genetic code
• Pleiotropy
• Multiple effects of one gene
• Genetic drift
• Changes in gene pool due to random chance
• Linkage to an adaptive trait
• Genetic hitchhiking

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Pre-adaptation

• Trait that evolved under different selective
  force co-opted for new function
• In evolution you dont always start from scratch

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Evolution

• Helps understand and answer the Why?
• Why are males and females different?
• Why are some animals hermaphrodites?
• Why do male peacocks have great big tails?

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Scale

• Answer Why? Questions at two scales
• Why do male birds sing in the spring?
• Proximate Causation
• Direct mechanisms that drive phenomena
• Ex. Rising testosterone levels due to changes in
  environment
• Ultimate Causation
• Addresses the evolutionary significance
• Ex. Song important in reproductive success-
  attracting a mate

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