EVOLUTION

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EVOLUTION

• AND NATURAL SELECTION

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WHAT WILL WE COVER?

• What is evolution?
• Evidence for evolution
• Darwins contributions
• How does evolution occur?
• Why should anyone care?

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EVOLUTION BIOLOGY

• Evolution is the unifying theme of biology
• Explains biology at every level from molecules to
  ecosystems
• Continues to transform medicine, agriculture,
  biotechnology, conservation biology, and various
  other fields
• Blgy wtht vltn s lk nglsh wtht vwls
• Ths s prtt hrd t rd, snt t?

4

• Nothing in biology makes sense except in light
  of evolution
• --Theodosius Dobzhansky

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WHAT IS EVOLUTION?

• Evolution can be defined as a change in the
  characteristics of a population over time
• Includes change within a species
• Microevolution
• Includes the formation of new species
• Macroevolution

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WHAT IS EVOLUTION?

• Evolution is a characteristic of populations, not
  of individuals
• Populations evolve, individuals do not

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EVOLUTION RELIGION

• There exists a perceived dichotomy between
  evolution and religion
• Are religion and evolution mutually exclusive?
• Can they coexist?

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EVOLUTION RELIGION

• The vast majority of educated people accept the
  reality of evolution
• Many of these same people have religious beliefs
• Even the pope acknowledges that evolution is
  compatible with christianity

I see! Evolution occurs!
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EVOLUTION RELIGION

• Certain religious beliefs are clearly
  incompatible with our understanding of evolution
• e.g. Various literalist, fundamentalist groups
• These religious beliefs are also incompatible
  with our understanding of astronomy, physics,
  chemistry, and numerous other disciplines

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EVOLUTION RELIGION

• The vast majority of scientists accept evolution
  to the exclusion of religion
• Over 93 of the members of the National Academy
  of Sciences are atheists or agnostics
• Numerous non-scientists concur

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CHARLES DARWIN

• Who is Charles Darwin?
• What did he do?
• When did he live?

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ANCIENT GREEKS

• Charles Darwin was not the first person to
  propose the idea of biological evolution
• This concept dates back at least as far as the
  ancient Greeks
• Not accepted by Aristotle, though
• Charles grandfather Erasmus Darwin was a noted
  and outspoken evolutionist
• Sadly, Charles parents werent nearly as astute

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JEAN BAPTISTE LAMARCK

• Charles Darwin was not the first person to
  propose a mechanism for biological evolution
• Jean Baptiste de Lamarck proposed a comprehensive
  mechanism for evolution in 1809
• 50 years before Darwins publication
• His proposed mechanism was incorrect
• Inheritance of acquired characteristics

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JEAN BAPTISTE LAMARCK

• Though Lamarcks mechanism for evolution was
  inaccurate, it did have accurate elements
• Evolution explains the fossil record
• Evolution involves adaptation to the environment

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CHARLES DARWIN

• Charles Darwins contributions were twofold
• Added to the body of evidence showing that
  evolution does occur
• Proposed a mechanism by which evolution occurs
• Natural selection

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CHARLES DARWIN

• Charles Darwins two main ideas
• Evolution explains lifes unity
• Natural selection is a cause of adaptive
  evolution

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DIVERSITY UNITY OF LIFE

• Descent with modification from a common ancestor
  (evolution) can account for the diversity and
  unity of life on the planet
• No other scientific concept can do this

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EVIDENCE OF EVOLUTION

• Evidence of evolutionary change come from
  multiple sources
• Biogeography
• Fossil record
• Comparative anatomy
• Comparative embryology
• Molecular biology
• Charles Darwin added to this body of knowledge
• This body of knowledge has also grown immensely
  since Darwins time

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BIOGEOGRAPHY

• The geographical distribution of species provides
  information supporting evolution
• Biogeography
• The flora and fauna viewed by Darwin had a
  distinct South American flavor
• Temperate South American species more closely
  resembled their tropical neighbors than they
  resembled temperate European species
• Nearby location is reflective of evolutionary
  ancestry

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BIOGEOGRAPHY

• Biogeography provides information supporting
  evolution
• Closely related species tend to be found in the
  same geographical region
• Similar ecological niches in distant regions are
  occupied by more distantly related species
• May appear superficially similar due to
  independent adaptations to similar environments

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BIOGEOGRAPHY

• Similar ecological niches in distant regions are
  occupied by more distantly related species
• e.g., The marsupial sugar glider and eutherian
  (placental) flying squirrel occupy similar niches
• Similarities in form are due to independent
  adaptations to similar environments
• Convergent evolution

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FOSSIL RECORD

• Organisms generally decompose rather rapidly
  after death
• In rare instances, they can become fossilized
• Hard-bodied organisms are still more likely to
  fossilize than soft-bodied organisms

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FOSSIL RECORD

• Fossilization can occur when remains are rapidly
  covered with silt, ash, etc.
• Regularly occurs during floods, storms,
  landslides, volcanic eruptions, etc.
• Protected from organisms higher on the food chain
  and from the general environment
• Lack of oxygen slows decomposition
• Soft parts generally decompose
• Hard parts can become mineralized and preserved
• Soft parts are rarely fossilized

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FOSSIL RECORD

• Fossilization can occur when remains are rapidly
  covered with silt, ash, etc.

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FOSSIL RECORD

• Fossils in sedimentary rock can provide a glimpse
  of some of the organisms present at various times

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FOSSIL RECORD

• Appearance of organisms in the fossil record
  reflects their evolutionary relatedness
• Prokaryotes ? eukaryotes
• Unicellular ? multicellular
• Invertebrates ? vertebrates
• Fish ? amphibians ? reptiles ?mammals and birds
• Inconsistent with simultaneous creation

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HISTORY OF LIFE
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CHORDATE EVOLUTION
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TRANSITIONAL FORMS

• The fossil record contains numerous transitional
  forms
• Forms linking two species or groups
• Abundant in the fossil record
• e.g., Whale evolution
• e.g., Horse evolution
• e.g., Bird evolution
• etc.

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TRANSITIONAL FORMS

• Modern whales lack legs
• Evolved from terrestrial ancestors with legs
• Many transitional forms have legs of various
  sizes

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TRANSITIONAL FORMS

• Modern whales lack legs
• Evolved from terrestrial ancestors with legs
• Many transitional forms have legs of various
  sizes

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TRANSITIONAL FORMS

• Ambulocetus is a transitional form in whale
  evolution
• 50 mya

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TRANSITIONAL FORMS

• Basilosaurus is another transitional form in
  whale evolution
• 40 mya

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TRANSITIONAL FORMS

• Students are expected to read (the slightly out
  of date) Hooking Leviathan by Its Past, by
  Stephen Jay Gould, which can be found at the
  following website
• http//www.stephenjaygould.org/library/gould_levia
  than.html

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TRANSITIONAL FORMS
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TRANSITIONAL FORMS
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TRANSITIONAL FORMS
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TRANSITIONAL FORMS

• Birds evolved from reptiles
• More specifically, they evolved from dinosaurs
• Avian dinosaurs
• Birds are appropriately classified within class
  Reptilia

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TRANSITIONAL FORMS

• The closest reptilian relatives of birds were the
  therapods
• Group of small, bipedal, carnivorous dinosaurs
• Many therapods were feathered

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TRANSITIONAL FORMS

• Archaeopteryx represents a transitional form in
  the evolution of birds from ancestral reptiles
• Features of ancestral reptiles
• Features of birds

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HOMOLOGY

• Descent with modification from a common ancestor
  can explain why certain related species share an
  underlying similarity
• Similarity resulting from common ancestry is
  termed homology
• Functions of these structures may be very
  different

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COMPARATIVE ANATOMY

• The view of evolution as a remodeling process can
  explain findings in comparative anatomy
• e.g., The forelimb of all mammals show the same
  arrangement of bones
• Similar due to shared ancestry
• Functions are very different
• Anatomical homologies

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COMPARATIVE ANATOMY

• The arms, forelegs, flippers, and wings of
  various mammals are termed homologous structures
• Variations of a structural theme present in a
  common ancestor

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COMPARATIVE ANATOMY

• Whales move in a manner similar to terrestrial
  mammals
• Spine is contorted vertically
• Fish move through lateral contortions

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COMPARATIVE ANATOMY

• Is a whale shark a whale or a shark?

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COMPARATIVE EMBRYOLOGY

• Early stages of embryonic development reveal
  additional anatomical homologies
• Comparative embryology
• e.g., Post-anal tails and pharyngeal pouches are
  common to all vertebrate embryos
• Develop into very different homologous structures
• e.g., Gills in fishes and parts of the ears and
  throat in humans

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VESTIGIAL ORGANS

• Some homologous structures are vestigial organs
• Structures of negligible importance to the
  organism
• Remnants of structures serving important
  functions in ancestral species
• e.g., Some snakes and whales retain vestiges of
  the pelvis and leg bones of walking ancestors

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VESTIGIAL ORGANS

• Humans possess numerous vestigial organs
• Appendix
• Body hair
• Erector pili muscles
• Wisdom teeth
• Coccyx

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COMPARATIVE ANATOMY

• Evolution does not fashion perfect organisms
• Can only modify existing structures and functions
• Often produces imperfect, yet functional, results
• e.g., The pandas thumb

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COMPARATIVE ANATOMY

• The natural world contains many instances of
  apparent perfection in form
• This seeming perfection could arguably have
  arisen from evolution or from some sort of divine
  creation
• Imperfection in nature is a hallmark of evolution
• Imperfection is expected from evolution
• Imperfection could be the mark of an bungling
  engineer, but not an impeccably skilled one

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MOLECULAR HOMOLOGIES

• Similarities are observed at the molecular level
• Molecular homologies
• e.g., The genetic code is universal
• Similarity due to the descent of all organisms
  from a common ancestor

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MOLECULAR HOMOLOGIES

• Similarities are observed at the molecular level
• e.g., DNA and protein differences mirror
  evolutionary relationships
• Similarities reflective of time since common
  ancestor

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MOLECULAR HOMOLOGIES

• Similarities are observed at the molecular level
• e.g., DNA, RNA, and protein differences mirror
  evolutionary relationships

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MOLECULAR HOMOLOGIES

• Many evolutionary relationships were established
  prior to the advent of molecular biology
• Darwinian evolution predicts that molecular
  similarities will accompany anatomical
  similarities
• In fact, they do
• This illustrates the predictive nature of
  evolution
• Molecular similarities are now used to establish
  molecular relationships when anatomical and other
  similarities are insufficient
• e.g., Invertebrates, bacteria, etc.

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CHARLES DARWIN

• Charles Robert Darwin was born in Shrewsbury,
  England in 1809
• Interested in nature since childhood
• Spent much of his childhood hunting, fishing,
  and collecting insects
• Initially studied medicine, then theology
• Many scientific scholars at that time were
  members of the clergy

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CHARLES DARWIN

• Charles Darwin served as a naturalist aboard the
  HMS Beagle
• Sailed from England in 1831
• Darwin was 22 years old at the time
• The primary goal of the voyage was to survey and
  map the South American coastline

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CHARLES DARWIN

• Darwin spent much of the next five years
  observing and collecting South American plants
  and animals
• Observed various adaptations to diverse
  environments
• Brazilian jungles, Argentine grasslands, Tierra
  del Fuego near Antarctica, Andes mountains
• Noted that South American temperate species were
  more similar to their tropical neighbors than to
  European temperate species
• Fossils had a distinct South American flavor

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CHARLES DARWIN

• Darwins voyage on the Beagle made him more aware
  that evolution occurs
• The more interesting question was how evolution
  occurs

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DARWINS INFLUCENCES

• The predominant view in Darwins time was that
  the earth was only a few thousand years old
• Inferred from biblical genealogies
• This erroneous view significantly altered how
  observations of the natural world were interpreted

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CUVIERS CATASTROPHISM

• Paleontology was largely developed by Georges
  Cuvier
• 1769 1832
• Noted that deeper strata bore fossils
  increasingly dissimilar from current life
• Noted that species appear and disappear between
  strata
• Inferred that extinctions were a common
  occurrence in the history of life

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CUVIERS CATASTROPHISM

• Cuvier was philosophically opposed to the concept
  of gradual evolutionary change
• Advocated catastrophism to explain his
  observations
• Speculated that each boundary between strata
  represented a catastrophe that destroyed many
  species
• Proposed that these catastrophes were usually
  local events
• Areas were repopulated through immigration

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CUVIERS CATASTROPHISM

• Cuvier proposed catastrophism to explain his
  observations within a framework dictated by his
  personal religious views

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HUTTONS GRADUALISM

• James Hutton is considered to be the father of
  modern geology
• 1726 - 1797
• Promoted the concept of gradualism
• Profound change can occur through the cumulative
  effects of slow but continuous processes
• Earths geologic features can be explained by
  currently operating gradual mechanisms

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HUTTONS GRADUALISM

• Huttons gradualism
• Valleys were formed by rivers wearing through
  rocks
• Sedimentary rocks were formed when particles
  eroded from land were carried by rivers to the
  sea

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LYELLS UNIFORMITARIANISM

• Charles Lyell incorporated Huttons ideas into
  the more comprehensive idea of uniformitarianism
• Principles of Geology
• Proposed that the same geologic processes are
  operating today as in the past
• Occurring at similar rates today and in the past
• e.g., Forces that build mountains and forces
  that erode mountains have not changed

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DARWINS INFLUENCES

• Darwin read Lyells Principles of Geology while
  aboard the Beagle
• Concluded that the physical evidence contradicted
  the traditional view of a young and static Earth
• The earth is far, far older than a mere few
  thousand years
• Darwin also personally witnessed an earthquake in
  Chile
• Noted that the coastline had risen by several
  feet
• Inferred that fossilized marine organisms high in
  the Andes had been raised by a series of such
  earthquakes

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DARWINS INFLUENCES

• Darwin read Lyells Principles of Geology while
  aboard the Beagle
• Realized that slow change over long periods of
  time can amount to significant change
• This applies to geological change
• This can also apply to biological change

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THOMAS MALTHUS

• Reverend Thomas Malthus was concerned with the
  social problems affecting human populations
• Essay on the Principle of Population
• Human population increase exponentially
• Food supply only increases linearly
• More individuals are produced than can be
  supported, resulting in many deaths
• Insufficient resources to support a population
  is the basis of social ills
• e.g., Famine, war, etc.

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DARWINS INFLUENCES

• Darwin was influenced by Malthus Essay on
  Populations
• Concluded that Malthus principles apply to all
  species, not just humans
• Insufficient resources lead to a struggle for
  existence
• Variation exists within a population
• Some individuals are better able to win this
  struggle
• Death is not random

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NATURAL SELECTION

• Darwin perceived that the evolution of new
  species involved adaptation to the environment
• Speciation resulted from the gradual accumulation
  of adaptations to a different environment

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NATURAL SELECTION

• It follows that any being, if it vary however
  slightly in any manner profitable to itself
  will have a better chance of surviving and thus
  be naturally selected
• -- Charles Darwin

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NATURAL SELECTION

• Evolutionary biologist Ernst Mayr has dissected
  the logic of Darwins theory of natural selection
  into three inferences (inescapable conclusions)
  based upon five observations

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NATURAL SELECTION

• Observation 1
• All species have such great potential fertility
  that their populations would increase
  exponentially if all individuals that are born
  reproduces successfully

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NATURAL SELECTION

• Observation 2
• Populations tend to remain stable in size, except
  for seasonal fluctuations
• Observation 3
• Environmental resources are limited

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NATURAL SELECTION

• Inference 1
• Production of more individuals than the
  environment can support leads to a struggle for
  existence among individuals of a population, with
  only a fraction of offspring surviving each
  generation

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NATURAL SELECTION

• Observation 4
• Individuals of a population vary extensively in
  their characteristics no two individuals are
  exactly alike

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NATURAL SELECTION

• Observation 5
• Much of this variation is heritable

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NATURAL SELECTION

• Inference 2
• Survival in the struggle for existence is not
  random, but depends in part on the hereditary
  constitution of the surviving individuals. Those
  individuals whose inherited characteristics best
  fit them for the environment are likely to leave
  more offspring than less-fit individuals

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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

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NATURAL SELECTION

• In summary
• Natural selection involves differential
  reproductive success
• Traits of individuals more reproductively
  successful increase in frequency
• Populations become better adapted to their
  environments

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OBSERVING EVOLUTION

• Many cases of evolutionary change have been
  observed
• Artificial selection of plants and animals
• Beak size in Galapagos finches
• Color of British peppered moths
• Antibiotic-resistant bacteria
• Evolution of HIV

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ARTIFICIAL SELECTION

• Plant and animal breeding involve artificial
  selection
• A special case of natural selection where humans
  act as the selective agent
• Individuals with desirable traits are selected
  for reproduction
• Significant change is rapid
• Greater change is possible over larger periods of
  time

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ARTIFICIAL SELECTION

• Artificial selection has produced the various
  breeds of dogs, cats, horses, cattle, etc.

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ARTIFICIAL SELECTION

• Corn (maize) is the product of artificial
  selection from teosinte

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ARTIFICIAL SELECTION

• Artificial selection has produced a variety of
  vegetables from a wild mustard ancestor

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NATURAL SELECTION

• Seed size and abundance change during droughts
• Changes in beak size and body size occur rapidly
  in populations of Darwins finches at such times

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NATURAL SELECTION

• Industrial pollution that alters the landscape
  results in a shift in coloration frequencies in
  the British peppered moth

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NATURAL SELECTION

• Antibiotic resistance evolves rapidly in
  bacterial populations repeatedly exposed to
  antibiotics
• Dealing with this problem requires an
  understanding of evolutionary biology

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NATURAL SELECTION

• HIV evolves incredibly rapidly
• Evolves too fast for ones immune system to keep
  up
• Rapidly evolves resistance to drugs
• It is the rapid evolution of this virus that
  makes HIV such a major global problem
• Dealing with this problem requires an
  understanding of evolutionary biology

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NATURAL SELECTION

• By the early 1940s, Darwin worked out the major
  features of natural selection as the means of
  evolution
• Darwin was hesitant to publish this work
• Darwin anticipated the uproar his ideas would
  cause amongst the religious
• He was an agnostic, but cared deeply for some
  people still viewing religion as worthwhile

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ALFRED WALLACE

• In 1958 Darwin received a manuscript from Alfred
  Russel Wallace
• British naturalist working in the West Indies
• Developed a theory of natural selection similar
  to Darwins

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ON THE ORIGIN OF SPECIES

• Wallaces manuscript and extracts from Darwins
  1944 essay were simultaneously presented to the
  Linnean Society in 1958
• Darwin completed and published his work in 1959
• On the Origin of Species
• Darwin received the majority of the credit for
  developing the concept of natural selection
• Darwins work preceded that of Wallace
• Darwins work was developed more extensively

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ACCEPTANCE OF EVOLUTION

• The majority of biologists accepted the
  occurrence of evolution within a decade of the
  publication of On the Origin of Species
• Acceptance of natural selection as evolutions
  mechanism took a bit longer

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HUMAN ANCESTRY

• "Humans are not the end result of predictable
  evolutionary progress, but rather a fortuitous
  cosmic afterthought, a tiny little twig on the
  enormously arborescent bush of life, which if
  replanted from seed, would almost surely not grow
  this twig again."
• - Stephen Jay Gould

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FACT AND THEORY

• Students are expected to read Evolution as Fact
  and Theory, by Stephen Jay Gould, which can be
  found at the following website
• http//www.stephenjaygould.org/library/gould_fact-
  and-theory.html

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REFERENCES

• Brooker, Robert J. Genetics, Analysis
  Principles, 2nd edition. McGraw-Hill Companies,
  Inc. 2005.
• Campbell, Neil A. and Reese, Jane B. Biology,
  7th edition. Pearson Education, Inc. 2005.
• Campbell, Neil A., Reese, Jane B., Taylor, Martha
  R., and Simon, Eric J. Biology, Concepts and
  Connections, 5th edition. Pearson Education,
  Inc. 2006.
• Gould, Stephen Jay. Evolution as Fact and
  Theory. Discover 2 (May 1981) p34 37.
• Gould, Stephen Jay. Hooking Leviathan by Its
  Past. Natural History 103 (May 1994) p8 15.
• Nester, Eugene W., Anderson, Denise G., Roberts,
  C. Evans Jr., and Nester, Martha T.
  Microbiology, A Human Perspective, 5th edition.
  McGraw-Hill Companies, Inc. 2007.