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Chapters 22-25 Evolution. Evolution. The definition of Evolution is: change over time Biological Evolution is: genetic change in population over time process by which modern organisms have descended from ancient organisms (slow change over long time)

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The definition of Evolution is:

  • change over time

Biological Evolution is:

  • genetic change in population over time
  • process by which modern organisms have descended from ancient organisms (slow change over long time)
    • Even relatively quick evolution takes hundreds of thousands of years
history of evolutionary theories
History of Evolutionary Theories
  • Plato (427-347 B.C.) 2 worlds – 1 perfect, 1 imperfect. No change in organisms
  • Aristotle (384-322 B.C.) Organisms placed on “ladder of complexity / perfection” (scala naturae) No change
  • Judeo-Christian culture tried to explain the Creator’s plan as observable, natural phenomena – Natural Theology
history of evolutionary theories1
History of Evolutionary Theories
  • Carolus Linnaeus (1707-1832) Designed modern taxonomic system (binomial nomenclature)
    • From this system, we can (he didn’t) now infer evolutionary relationships between different groups
  • Geologists:
    • Georges Cuvier
    • James Hutton
    • Charles Lyell
history of evolutionary theories2
History of Evolutionary Theories
  • Georges Cuvier (1769-1832) helped develop Paleontology – study of fossils
    • Discovery of fossils (extinct species, similarities to modern species) put some doubt into Earth’s age and the origin of species
    • Cuvier explained differences in strata with “catastrophism” – floods, droughts, volcanoes, etc. changed local areas drastically over short periods of time
      • Organisms did not change, just migrate
history of evolutionary theories3
History of Evolutionary Theories
  • James Hutton (1726-1797) proposed that rocks, mountains, and valleys have been changed by water, wind, temperature, volcanoes, and other natural forces
  • He described the slow processes that shape Earth as “gradualism”
history of evolutionary theories4
History of Evolutionary Theories
  • Charles Lyell (1797-1875) – agreed with Hutton and said that scientists must always explain past events in terms of observable, PRESENT events and processes (“uniformitarianism” – what happens today happened yesterday)
  • They theorized Earth was much older than a few thousand (6,000) years, which didn’t set well in the traditional timeframe of Creationism
age of the earth
Age of the Earth
  • We now know Earth is approximately 4.5 billion years old
  • Darwin used the work of Hutton and Lyell as a basis for his theories of slow change over time. Darwin’s work was a biological duplicate of Hutton and Lyell’s works in geology.
geologists study earth s rocks
Geologists study Earth’s rocks
  • Fossils are preserved remains of ancient organisms
  • As fossils are found that don’t resemble organisms today, evidence increases that Earth has changed and that organisms have changed with it
  • Biologists and geologists date Earth’s past with the help of rocks
geological time scale
Geological Time Scale
    • Technique used to determine age of fossils relative to other fossils in different strata
    • This technique is VERY approximate
geological time scale1
Geological Time Scale
    • Using radioactive elements in rock that decay at a steady rate to determine age
    • Decay measured in terms of HALF-LIFE
      • Half-life – time required for half the radioactive atoms in a sample to decay
radioactive decay
Radioactive Decay
  • During radioactive decay, the atoms of one element break down to form something else

Lose a proton

6 protons

4 neutrons

5 protons

4 neutrons

Rocks contain radioactive elements, each having a different half-life


Uranium-238 Lead-206 HL = 4.5 B yrs

Potassium-40 Argon-40 HL = 1.3 B yrs

Carbon-14  Nitrogen-14 HL = 5770 yrs






  • Scientists often date rocks using Potassium-40, which decays to form the stable element Argon-40
  • It has a half life of 1.3 billion years
  • This is used to date the oldest rocks on earth


1.3 B yrs

2.6 B yrs

Uranium and Potassium are useful for dating rocks
  • Carbon-14 is useful for dating things that were once alive such as wood, natural fiber, or cloth
    • C-14 is in the atmosphere; living things take it in their cells. After the organism dies, it doesn’t take in any more C-14. We can then compare the amounts of C-14 to N-14, knowing its half-life, to determine the age of the sample
fossil evidence
Fossil Evidence
  • Found in Sedimentary rock: layers of sand, silt, and clay in streams, lakes, rivers, and seas form rock that may have trapped living organisms
  • Fossil records – Show change over time. Some time frames are missing, but will show change of climate and geography.
  • Ex: Shark teeth in Utah
    • How can this be?
jean baptiste de lamarck 1744 1829
Jean Baptiste de Lamarck (1744-1829)
  • He also recognized that organisms were adapted to their environments and that they change
  • He relied on three ideas:
    • A desire to change (innate drive for perfection)
    • Use and disuse (Giraffe’s necks and vestigial organs)
    • Inheritance of acquired characteristics
darwin s dilemma
Darwin’s Dilemma
  • Set sail around the world in 1831 on HMS Beagle on a 5 year voyage
  • He had prior knowledge of geology (Lyell was a good friend) and agriculture that helped influence the development of his theory
  • Anchored all along the way and took samples from each place
darwin s dilemma1
Darwin’s Dilemma
  • He collected and studied beetles from Brazil, birds from Chile, and iguanas, tortoises, and finches from the Galápagos Islands
  • He noticed similarities between mainland (Ecuador) and Galapagos finches
  • Later, he noticed differences in beak size among finches from different islands in the Galapagos
darwin s dilemma2
Darwin’s Dilemma
  • Thomas Malthus – wrote paper on population growth in Great Britain
    • Population grows exponentially
    • Limiting factors on growth (carrying capacity)
      • Food
      • Area
      • Resources
darwin s dilemma3
Darwin’s Dilemma
  • Darwin applied Malthus’, Hutton’s, and Lyell’s work to species’ ability to change, and called the mechanism Natural Selection
    • Nat.Sel.: Process by which organisms with favorable variations survive and produce more offspring than less well-adapted organisms
  • He was sure Nat.Sel. was true, but he feared public ridicule. So, he kept his ideas to himself
darwin s dilemma4
Darwin’s Dilemma
  • Alfred Russel Wallace (1823-1913), working independently, came to the same conclusions as Darwin
  • He sent a manuscript to Darwin, basically for proofreading
  • “I never saw a more striking coincidence… so all my originality, whatever it may amount to, will be smashed.” – Charles Darwin
    • Letter to Charles Lyell, June 18, 1858
  • Darwin quickly abridged and published his work “On the Origin of Species”
darwin s natural selection
Darwin’s Natural Selection
  • Ernst Mayr, an evolutionary biologist, has dissected the logic of Darwin’s theory into three inferences based on five observations (Pg. 435)
  • Observations:
    • Tremendous fecundity
    • Stable populations sizes
    • Limited environmental resources
    • Variation among individuals
    • Heritability of some of this variation.
darwin s natural selection1
Darwin’s Natural Selection
  • Observation #1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully.
darwin s natural selection2
Darwin’s Natural Selection
  • Observation #2: Populations tend to remain stable in size,except for seasonal fluctuations.
  • Observation #3: Environmental resources are limited.
darwin s natural selection3
Darwin’s Natural Selection
  • Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation.
darwin s natural selection4
Darwin’s Natural Selection
  • Observation #4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike.
  • Observation #5: Much of this variation is heritable.
darwin s natural selection5
Darwin’s Natural Selection
  • Inference #2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals.
    • Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less fit individuals.
darwin s natural selection6
Darwin’s Natural Selection
  • Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.
evidence in living organisms
Evidence in Living Organisms
  • Comparative embryology:
    • All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches
      • Ernst Haeckel made early drawings – later exposed as frauds.
      • Gave fuel to anti-evolutionists
evidence in living organisms1
Evidence in Living Organisms
  • Comparative embryology:
    • These anatomical similarities indicate similar genetics are at work
    • Become more dissimilar as they grow
      • Cell specialization and differentiation
    • Common ancestor?
evidence in living organisms3
Evidence in Living Organisms
  • Comparative anatomy:
    • Homologous Structures
    • Analogous Structures
    • Vestigial Organs
evidence in living organisms4
Evidence in Living Organisms
  • Homologous Structures – structures that are similar in anatomy, but may serve very different functions
    • Ex: cat, whale, and human forearm

Homologous Structures





evidence in living organisms5
Evidence in Living Organisms
  • Analogous Structures – structures that serve similar functions, but have evolved independently of each other

Not homologous;analogous

Not homologous;not analogous

Homologous;not analogous

Homologous; analogous

evidence in living organisms6
Evidence in Living Organisms.
  • Vestigial organs – organs that have little or no purpose in the organism; may become smaller or even disappear
    • Ex: Tailbone or appendix in humans
    • Ex: Tiny leg bones in snakes (boas and pythons) thought to come from 4 legged ancestor
evidence in living organisms7
Evidence in Living Organisms
  • Comparative biochemistry and molecular biology:
    • All cells have DNA, RNA, ribosomes, the same 20 amino acids and use ATP to do work
    • Similarities in biochemistry indicate relationship
evidence in living organisms8
Evidence in Living Organisms
  • Cytochrome c is a highly conserved respiratory protein containing 104 amino acids in humans
evidence in living organisms9
Evidence in Living Organisms
  • Amino acid differences of hemoglobin between species
what homologies tell us
What Homologies tell us…
  • Similarities in structure and chemistry provide powerful evidence that all living things evolved from a common ancestor
  • Darwin Concluded:
    • Living organisms evolved through gradual modifications of earlier forms  descent with modification
what similarities tell us
What Similarities tell us…
  • Two types of evolution can account for homologous AND analogous structures
    • Convergent evolution
    • Divergent evolution
what similarities tell us1
What Similarities tell us…
  • Divergent evolution – two species evolve from a common ancestor (speciation)
    • They share similarities in anatomy, biochemistry, and embryology due to common ancestry
    • Explains homologous structures
what similarities tell us2
What Similarities tell us…
  • Convergent – two species apparently becoming more similar
    • Two species have adapted in similar ways to similar environmental conditions
    • NOT due to common ancestry
    • Explains analogous structures
convergent evolution
Convergent Evolution
  • Ocotillo from California and allauidi from Madagascar have evolved similar mechanisms for protecting themselves
convergent evolution1
Convergent Evolution
  • Adaptive radiation of anoles has occurred on the islands of the Greater Antilles in a convergent fashion. On each island, different species of the lizards have adapted to living in different parts of trees, in strikingly similar ways.
diversity of life
Diversity of Life
  • Fitness:
    • Physical traits and behaviors that enable organisms to survive and reproduce in their environment arises from adaptation.
  • Adaptation allows species to be better suited to their environment and therefore can survive and reproduce.
evolution on different scales
Evolution on Different Scales
  • Microevolution – generation-to-generation change in a population’s allele frequencies
  • Macroevolution – origin of new taxonomic groups; speciation
4 driving forces behind evol
4 Driving Forces behind Evol.
  • Mutation
    • Any change in the original DNA
    • ONLY ultimate source of variation in a population
  • Gene Flow
    • Movement of genes either into or out of a population
    • Migration – Immigration (add alleles) and Emigration (subtract alleles)
4 driving forces behind evol1
4 Driving Forces behind Evol.
  • Genetic Drift
    • Change in the allele frequency in a small population by chance alone
      • Bottleneck Effect
      • Founder Effect
4 driving forces behind evol2
4 Driving Forces behind Evol.
  • Genetic Drift
    • Bottleneck Effect: population undergoes a high mortality rate; genetic variation decreases dramatically
    • Ex: Cheetahs
4 driving forces behind evol3
4 Driving Forces behind Evol.
  • Genetic Drift
    • Founder Effect: few individuals leave a large population to start their own; gene pool is very limited
    • Ex: polydactyly in PA Amish
4 driving forces behind evol4
4 Driving Forces behind Evol.
  • Selection
    • Natural – differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment
      • Nature does the selecting
4 driving forces behind evol5
4 Driving Forces behind Evol.
  • Selection (Natural)
    • Resistance – overuse of insecticides and antibiotics have bred resistant species of bugs and germs
4 driving forces behind evol6
4 Driving Forces behind Evol.
  • Selection
    • Artificial – breeding of domesticated plants and animals
      • Humans intentionally do the selecting
      • Cabbage, cauliflower, Brussels sprouts, kale, kohlrabi and broccoli have a common ancestor in one species of wild mustard
4 driving forces behind evol7
4 Driving Forces behind Evol.
  • Problems with artificial selection – not enough genetic variation
4 driving forces behind evol8
4 Driving Forces behind Evol.
  • Selection (Sexual)
    • Intrasexual selection – selection within the same sex (competition, usually between males
        • Competition, usually between males
        • Exaggerated anatomy

Bighorn Sheep

Rocky Mountain Elk

Five-horned Rhinoceros Beetles


4 driving forces behind evol9
4 Driving Forces behind Evol.
  • Selection (Sexual)
    • Intersexual selection – one sex selects mate based on phenotypes
    • Exaggerated anatomy
Selection can influence populations in three major ways:
    • Directional Sel.
    • Stabilizing Sel.
    • Disruptive (diversifying) Sel.
directional selection
Directional Selection
  • Environment selects against one phenotypic extreme, allowing the other to become more prevalent
disruptive selection
Disruptive Selection
  • Environment selects against intermediate phenotype, allowing both extremes to become more prevalent
stabilizing selection
Stabilizing Selection
  • Environment selects against two extreme phenotypes, allowing the intermediates to become more prevalent
key points
Key Points
  • Natural selection does not cause genetic changes in individuals.
  • Natural selection acts on individuals; evolution occurs in populations.
  • Evolution is a change in the allele frequencies of a population, owing to unequal success at reproduction among organisms bearing different alleles.
  • Evolutionary changes are not “good” nor “progressive” in any absolute sense.
evolutionary theory
Evolutionary Theory
  • Foundation on which the rest of the biological science is built. Collection of carefully reasoned and tested hypotheses about how evolutionary change occurs.
  • What is a species?
    • Biological definition: a group of closely related organisms (population) that can interbreed to produce fertile, viable offspring
  • Why can’t/don’t populations interbreed?
    • Prezygotic barriers
    • Postzygotic barriers
prezygotic barriers
Prezygotic Barriers
  • Ecological (habitat) isolation – pops live in different habitats and do not meet
    • Parasites generally don’t transfer hosts
  • Temporal isolation – active or fertile at different times
    • Flowering plants pollinate on different days or different times of the day
prezygotic barriers1
Prezygotic Barriers
  • Behavioral isolation – differences in activities
    • Mating calls or actions are different
prezygotic barriers2
Prezygotic Barriers
  • Mechanical isolation – mating organs do not fit or match
    • Enough said
  • Gametic isolation – gametes cannot combine
    • Sperm destroyed in “different” vaginal cavity
    • Sperm and egg don’t fuse due to different membrane proteins
postzygotic barriers
Postzygotic Barriers
  • Hybrid inviability – hybrid zygotes fail to develop or reach sexual maturity
  • Hybrid infertility – hybrids fail to produce functional gametes
  • 2 or more mechanisms may occur at once
  • Ex: Bufo americanus and Bufo fowleri are ecologically, temporally, and behaviorally isolated
  • Bufo americanus breeds in early spring in small, shallow puddles or nearby dry creeks
  • Bufo fowleri breeds in late spring in large pools and streams
  • Their mating calls also differ
limitations of biological species concept
Limitations of Biological Species Concept
  • How do you classify organisms that:
    • have the potential to interbreed, but do not do so in nature?
    • do not reproduce sexually?
    • exist only as fossils?
  • Alternative species concepts (ecological, pluralistic, morphological, genealogical) help address limitations
modes of speciation
Modes of Speciation
  • Allopatric (Greek, allos = other; Latin, patria = homeland)
  • Speciation due to geographic separation
    • Barrier stops gene flow between populations
    • Evolutionary change acts independently on each pop to establish reproductive barriers
Mitochondrial DNA analysis has shown that certain tamarin monkey pops (those separated by wide rivers) are diverging toward speciation
  • Where the Amazon is very wide, tamarins on one side are brown, but on the other side are white. Where the Amazon is narrow, tamarins of both colors are found on either side
allopatric speciation

A. leucurus

A. harrisi

Allopatric Speciation
  • Birds can move freely across the gorge of the Grand Canyon; squirrels cannot
  • Two species arose when their original pop was disrupted by the carving of the canyon
A. harrisi

A. leucurus

allopatric speciation1
Allopatric Speciation
  • If not given enough time, speciation will not occur
  • Also, even if they do come back together, they need to interbreed to be the same species
allopatric speciation2
Allopatric Speciation
  • Figure 24.11
  • Adaptive Radiation: evolution of many diversely-adapted species from a common ancestor
  • Ex: Hawaiian archipelago
sympatric speciation
Sympatric Speciation
  • Sympatric (Greek, sym = together; Latin, patria = homeland)
  • Speciation occurs in populations that share a habitat
  • Results from:
    • Ecological isolation
    • Polyploidy (number of sets of chromosomes increases)
sympatric speciation1
Sympatric Speciation
  • Polyploidy (number of sets of chromosomes increases)
  • A result of accidents in meiosis
will speciation occur
Will Speciation Occur?
  • p + q = 1
  • p2 + 2pq + q2 = 1
  • Will speciation occur? You tell me!
  • Hardy-Weinberg PPT 1
  • Hardy-Weinberg PPT 2
evolutionary time scales
Evolutionary Time Scales
  • Evolution can take a long time or can occur relatively quickly
    • Gradualism
    • Punctuated Equilibrium
evolutionary time scales1
Evolutionary Time Scales
  • Gradualism – big evolutionary changes are the result of many small ones over a long period of time
evolutionary time scales2
Evolutionary Time Scales
  • Punctuated Equilibrium – speciation occurs fairly rapidly then remain constant
evolutionary novelties
Evolutionary Novelties
  • Unique and highly specialized organs seem to complicated to have been naturally selected
  • Ex: eyes are really just photoreceptors; some are more developed, but all do the basic function: receive light
evo devo
  • Evolutionary development
  • A field of interdisciplinary research that examines how slight genetic divergences can become magnified into major morphological differences between species
evo devo1
  • By blocking expression of one gene, researchers forced a chicken’s foot to develop to resemble a duck’s foot
  • Two embryos from the same animal
evo devo2
  • Left, a normal chicken leg will develop
  • Right, a normal duck leg will develop… from a chicken embryo
  • Chicken leg: scaled with 4 digits
  • Duck leg: smooth and webbed
  • Duck legs, due to one genetic evolutionary difference, help ducks do many things chickens cannot, like swim