Download Chapter 22: Descent w/ Modification Aristotle (384

Chapter 22: Descent w/ Modification
Aristotle (384-322 BC)
 Greek philosopher
 Viewed species as fixed & unchanging
 Scala Naturae – ladder arrangement; more complex organisms on higher rungs
Carolus Linnaeus (1707-1778)
 Species are matched to their environment = evidence of Divine Creation
 Created taxonomy for classifying organisms
o Binomial naming = Genus species; e.g. Homo sapiens
Jean-Baptiste de Lamarck (1744-1829)
 French Biologist, published in 1809
 Species evolve thru use & disuse of body parts & inheritance of acquired characteristics
 Giraffe’s neck
 Mechanisms he proposed are unsupported by evidence
Fossils
 Remains or traces of organisms from past
 Usually in sedimentary rock
o Strata – layers of rock
 Others study of fossils laid groundwork for Darwin’s ideas
Georges Cuvier (1769-1832)
 French scientist; developed Paleontology
o Study of fossils
 Old strata had different life forms than present day; species disappeared & new ones appeared
 Catastrophism
o Each boundary b/w strata represents a catastrophe
James Hutton (1726-1797)
 Scottish geologist
 Said earth’s geologic features explained by gradual mechanisms still operating today
o e.g. valleys formed by rivers wearing thru rocks
Charles Lyell (1797-1875)
 Believed in Hutton’s gradual changes
 Uniformitarianism
o Mechanisms of change are constant over time
o i.e. Today’s rate same as past
 Strongly influenced Darwin’s thinking
Hutton/Lyell to Darwin
 Most believed Earth was a few thousand years old
 If rivers made canyons in slow gradual change, then Earth older
 If slow change works in geology, why not biology
Charles Darwin (1809-1882)
 Studied medicine & then theology at Cambridge University
 After graduation, took unpaid job as naturalist on the Beagle (5 yr voyage)
o Collected specimens of South American plants & animals
o Observed adaptations of species that inhabited diverse environments
Adaptation
 Traits of organisms that enhance survival & reproduction
 Maladaptive Trait – negative trait
Timeline
 1844 – Darwin wrote essay on origin of species & natural selection; anticipates uproar, doesn’t publish
 1858 – Gets manuscript from Alfred Russell Wallace; proposed theory of natural selection similar to
Darwin’s
 Darwin quickly finished The Origin of Species & published it the next year
The Origin Of Species
o Developed two main ideas:
 Descent with modification: explains life’s unity & diversity
 Natural selection is a cause of adaptive evolution
o Descent with Modification
 Idea that all organisms are related thru descent from an ancestor that lived in remote past
 ‘Evolution’ not used in 1st ed.
 History of life is like a tree w/ branches representing life’s diversity
o Artificial Selection
 Darwin noted that humans have modified other species
 Selectively breeding individuals w/ desired traits
 e.g. dogs, cattle, crops
o Darwin described 4 observations of nature & drew 2 inferences…
 Observation #1 – members of a population often vary greatly in their traits
 Observation #2 – traits are inherited from parents to offspring
 Observation #3 – all species are capable of producing more offspring than environment can
support (Malthus)
 Observation #4 – owing to lack of food or resources, many of these offspring don’t survive
 Inference #1 – Individuals whose inherited traits give them a higher probability of
surviving & reproducing in an environment tend to leave more offspring than others
 Individuals that are well suited to their environment tend to leave more offspring
than other individuals
 Inference #2 – unequal ability of individuals to survive & reproduce will lead to
accumulation of favorable traits in population over generations
 Over time, favorable traits accumulate in the population
o Environmental Change
 3 Responses…
o Adapt
o Migrate
o Go extinct
o Steps to Evolution
 Mutation – DNA change
 Reproductive cell
 Spontaneous or mutagens
 Natural Selection
 Adaptation allows organism to leave more offspring
 Time – many generations pass
o Common Misconceptions
 ‘Survival of fittest’ = ‘Survival of strongest’
 Organisms match environment & environments change
 Traits evolve b/c they are needed or wanted
 Differences in traits must first be present
 Individuals evolve
 Populations evolve, NOT INDIVIDUALS
o Summary
 Genes mutate
 Individuals are selected for/against
 Populations evolve
o Selection Types
 Stabilizing Selection
 Middle ground favored
 Directional Selection
 One extreme favored
 Disruptive Selection
 Both extremes favored
o
Evidence?
 Peppered Moth Evolution
 England (normally) has light colored trees; light moths dominant
 Industrial revolution causes trees to be soot-covered; dark moths dominant
 Endler’s Guppies
 Studied effects of predators on wild guppy populations
o Brightly colored males are more attractive to females
 Also more vulnerable to predation
 Killifish eat only colorless juvenile guppies
o Adults in killifish pond tend to be brightly colored
 Cichlids prey on adults (esp. bright colored)
o Adults in cichlid pond tend to be drab colored
 HIV (Human Immunodeficiency Virus)
 Retro-virus; genetic material is RNA
 Has just 3 enzymes
o Reverse Transcriptase – make RNA into DNA
 No error correction, rapid mutations
o Integrase – integrates viral DNA into host DNA
o Protease – cuts 3 polypeptides; makes them active
 Evolution of Drug-Resistant HIV
o Reverse transcriptase (RT) makes DNA out of HIV’s RNA genome
o Drug ‘3TC’ mimics cytosine (C) nucleotide
o Some RT enzymes pick up 3TC (instead of regular C) & DNA synthesis is
blocked
o Problem: not all RTs are fooled by drug 3TC; pick up normal C
 Greater reproductive success = increase in #
o Population of HIV viruses has developed resistance to 3TC
 Fossil Record Evidence
 Evidence of extinctions, new groups, & changes within groups over time
 Darwin ideas predict that evolutionary transitions should leave signs in fossil
record
 Paleontologists have discovered fossils of many transitional forms
 Homology
 Similarity resulting from common ancestry
 Structural, Embryological, & Molecular
 Homologous Structures
o Same body part on different species that arose from a common ancestor
o Mammal Forearms
 Same bone arrangement – shoulder to fingertips
 Comparative Embryology
o Studies anatomical homologies of embryos
 Not visible in adults
o Chordates – notochord, dorsal hollow nerve cord, post-anal tail,
pharyngeal gill slits
 Vestigial Structures
o Remnants of features that served functions in organism’s ancestors
o Snakes w/ parts of pelvis & hind limbs
o Wisdom teeth
 Molecular Homology
o Genes shared among organisms inherited from a common ancestor
o All organisms use DNA or RNA
o Humans – Humans = 99.9% genes
o Humans – Chimps = 98%
o Humans – Roundworms = 50%
o Many different organisms use hemoglobin; all same gene
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Convergent Evolution
 Evolution of similar (or analogous) features in distantly related groups
 Analogous Structures
o Similar function as another organism, but different structure
Biogeography
 Geographic distribution of species
 Endemic species – found in only one place on Earth
 Islands often have endemic species that are closely related to species on nearest
mainland or island (e.g. Galapagos)
 Pangaea – all continents connected
o Began breaking apart 200 million years ago
o 20 million years ago, continents were w/in a few hundred km of where
they are today
o Continental drift – slow movement of continents over time
 Understanding drift & modern distribution of species allows
predictions of when & where groups evolved