Chapter 15: Evolution

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Chapter 15 EvolutionEvidence and Theory
15-1 The Fossil Record
15-2 Theories of Evolution
15-3 Evolution in Process
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15-1 The Fossil Record
I. Nature of Fossils (physical EVIDENCE for
evolution)

• Organisms appeared, LASTED for periods of time,
  BUT disappeared.
• NOTE MICROSCOPY ? Too much DETAIL for fossils
  to be simple rock formations (Robert Hooke,
  1700s).

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(1) Fossil (e.g., Types sedimentary fossils,
molds and casts)

• TRACE of a dead organism, usually with HARD
  MINERALS replacing tissues of an organism
  (leaving ROCK-LIKE structures).

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(2) Sediment (fossils form INSIDE sedimentary
rock)

• Dust, sand, OR mud deposited in LAYERS by wind
  or water
• NOTE Traps the HARDEST body parts of an
  organism to become fossilized (shell, bones,
  teeth, woody stems).

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(3) Mold

• HOLLOW fossil formed by sediment ENCASING a dead
  organism becomes filled with HARD minerals,
  forming a CAST of an organism.

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(4) Cast

• Rock-like MODEL of an organism resulting from a
  MOLD filled in with HARD minerals.

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II. Distribution of Fossils (Nicholas Steno,
1669)

• Earths GEOLOGICAL and BIOLOGICAL history are
  recognized by Stenos Law of Superposition.

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(1) Law of Superposition

• SUCCESSIVE layers of sediment are deposited on
  TOP of one another by wind and water ? GEOLOGICAL
  STRATA.

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(2) Stratum (pl. strata)

• Geological layer showing its RELATIVE age with
  respect to OTHER strata above (YOUNGER) and below
  (OLDER).

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(3) Relative Age (estimates VARY due to
DEPOSITION and EROSION)

• Age with respect to OTHER strata based upon its
  POSITIONING (also can infer the AGE of the
  FOSSILS contained).

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Critical Thinking
(1) What may you be able to conclude if you find
identical examples of a fossilized organism in
TWO adjacent geological strata?
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(4) Absolute Age (a form of quantitative data)

• Determined by RADIOACTIVE DATING of materials
  isolated from within a stratum.

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(A) Succession of Forms (Prokaryotes ? Modern
Humans)

• Fossil-bearing strata show species have CHANGED
  over time, possibly becoming EXTINCT (replaced)
  by newer forms.

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(1) Extinct (opposite extant)

• NO LONGER present due to SELECTIVE PRESSURES and
  confirmed through fossilized remains.

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(2) Mass Extinction (fossil evidence)

• Period where LARGE numbers of species
  disappeared due to DRASTIC environmental
  pressures.
• (i.e., Widespread volcanic activity, or asteroid
  impacts (ash dust theory))

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(B) Biogeography (Extinct VS. Extant)

• NEW organisms ARISE in environments where
  SIMILAR forms already inhabit (shared selective
  pressures yield similar phenotypes).

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15-2 Theories of Evolution
I. Jean Baptiste de Lamarcks Explanation (of HOW
species change1800s)

• Claimed ACQUIRED traits COULD be passed on to
  offspring
  (i.e., Theory of Acquired Characteristics).

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(1) Acquired Traits (CANNOT be passed down)

• Are NOT determined by genes BUT by the
  ENVIRONMENT.

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Critical Thinking
(2) If a favorable trait INCREASES the lifespan
of an organism WITHOUT affecting reproductive
success, does it contribute to EVOLUTION?
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II. The Beginning of Modern Evolutionary Thought
(Darwin and Wallace)

• GENETIC traits (NOT acquired traits) could be
  PASSED DOWN from parent to offspring via genes.

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(1) Natural Selection (drives the process of
EVOLUTION)

• Individuals BEST adapted will reproduce MORE
  ?thus OVER time, MOST FIT are those with MOST
  offspring.

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Critical Thinking
(3) The process of natural selection throughout
the history of life on Earth has resulted in the
success of some species and the extinction of
other species. Why has natural selection NOT
resulted in the existence of a SINGLE
best-adapted species?
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(2) Population (SMALLEST unit CAPABLE of evolving)

• Interbreeding group of same species (e.g., a
  populations GENE POOL consists of the TOTAL
  ALLELES held by that species).

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(A) Charles Darwin (1831-1836H.M.S. Beagle)

• Naturalist collected DATA on species of around
  the worldinterested in BIODIVERSITY and
  GEOGRAPHY.

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(B) Voyage of the Beagle (5 years, WIND-driven
ship)

• A book (Principles of Geology)influenced Darwin
  on the principles of UNIFORMITARIANISM.

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(1) Uniformitarianism (e.g., fossils of seashells
in the mountains)

• Earths HABITATS have been SHAPED (changed)
  through SLOW processes that operate OVER time.

NOTE This influenced Darwin to believe
modifications of ENVIRONMENTS required LONG
periods of time, much like the CHANGES it would
take SPECIES to ADAPT to these CHANGES (i.e.,
speciation).
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(C) Analysis of Darwins Data (on geography AND
biodiversity)

• Supported adaptive radiation of FINCH and
  TORTOISE populations that dispersed over
  Galapagos Islands (West of S. America).

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(D) Publication of The Origin of Species (1859)

• Used data to propose 2 THEORIES supporting HOW
  the process of EVOLUTION occurs in a population.

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III. Darwins Theories (following 5 year H.M.S.
Beagle voyage)

• Theory 1 DESCENT WITH MODIFICATION, occurs
  with EVERY species.

• Theory 2 MODIFICATION BY NATURAL SELECTION
  drives EVOLUTION to occur.

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(A) Descent with Modification

• NEWER forms are the MODIFIED DESCENDANTS of
  OLDER species.

(i.e., All species have DESCENDED from ONE or a
FEW ORIGINAL types of life remote, COMMON
ANCESTORS are common to many species).
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(B) Modification by Natural Selection (requires a
DIVERSE gene pool)

• NATURAL forces ACT UPON the GENETIC VARIATION
  within a population (resulting in VARYING degrees
  of FITNESS).

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DARWINS THEORY OF EVOLUTION HOLDS FOUR TENETS
(influenced by colleague Thomas Malthus)
(1) Populations will naturally grow BEYOND the
environmental capacity leading to a STRUGGLE for
existence (Malthuss work with populations).
(2) Individuals within a POPULATION show
VARIATION due to mutations AND genetic
recombination.
(3) The VARIATION is ACTED UPON (natural
selection) allowing MOST FIT members to survive
and YIELD MORE OFFSPRING.
(4) Over TIME (and through evolution), the gene
frequencies (i.e., GENE POOL) of the population
WILL CHANGE (and thus, traits WILL CHANGE).
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(1) Adapt (adaptations ARE phenotypes that aid
FITNESS)

• Adaptation RESULTS in an INCREASED number of
  FAVORABLE genes.

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(2) Fitness (Darwinian Fitness)

• NUMBER of VIABLE offspring an individual
  producesi.e., fitness IS measured by OFFSPRING
  COUNT.

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Critical Thinking
(4) In recent years, paleontologists have claimed
that in some cases the evolution of a new species
occurs quite suddenlyin LESS than a thousand
years. Darwin stated that evolution was a
gradual process. What effect may GENERATION TIME
have on evolution RATE?
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(3) Adaptive Advantage (over disadvantage)

• Is defined when an INHERITED TRAIT is known to

(1) Enhance an ability to OBTAIN NUTRITION.
(2) Enhance an ability to successfully MATE
yielding offspring.
(3) Enhance an ability to EVADE predation.
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15-3 Evolution in Process
I. Evidence of Evolution

• MODERN organisms (homologous AND analogous
  structures)we can see CHANGE occurred.

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(A) Homologous and Analogous Structures (i.e.,
divergent convergent evol.)

• MORPHOLOGY may OR may NOT reflect a COMMON
  ANCESTOR.

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(1) Homologous Structures (formed through
DIVERGENT evolution)

• Similar structures originated in a SHARED
  ancestor
  (e.g., changed the ORIGINAL to meet
  changing environmental forces).

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(2) Analogous Structures (formed through
CONVERGENT evolution)

• Structures serve similar FUNCTIONS, BUT
  organisms do NOT share a RECENT COMMON ANCESTOR
  (anatomical differences TOO great).

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(B) Vestigial Structures

• Useful to an ANCESTRAL organism but are NO
  longer useful in the MODERN-day descendant.

(1) Vestigial (preserved REMNANT of evolution)

• Evolution tends to be CONSERVATIVE, eliminating
  ONLY features that REDUCE fitness. (e.g.,
  tailbone, appendix, pelvic bones in snakes).

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Critical Thinking
(5) Many vestigial traits, such as the human
tailbone, seem to be largely NEUTRAL, that is,
neither beneficial nor harmful. The APPENDIX is
an example of a vestigial structure in humans.
How might having an appendix be HARMFUL to humans?
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(2) Conserved (Structures)

• Remain UNCHANGED throughout MUCH of evolutionary
  history of a species, (for not completely
  understood reasons).

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(C) Similarities in Embryology (developmental
similarity)

• ALL vertebrate embryos INITIALLY appear THE SAME
  (limb buds, backbone, eyes), BUT the similarities
  FADE.

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(D) Similarities in Macromolecules (MOLECULAR
evidence for evolution)

• Shared DNA, RNA, AND AA sequences MAY confirm
  evolutionary histories suggested by FOSSILS,
  MORPHOLOGY, AND EMBRYOLOGY.

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II. Patterns of Evolution (3 PATTERNS)

• Change RESULTS from changing demands of
  ENVIRONMENTS.

(1) Co-evolution
(2) Convergent Evolution
(3) Divergent Evolution
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Critical Thinking
(6) Some MONARCH butterflies contain chemicals
that are TOXIC to birds. Another species of
butterfly, the VICEROY, has some protection from
predation because it closely RESEMBLES the
monarch. What pattern of evolution is
illustrated by THIS example?
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(A) Coevolution

• Change of 2 or MORE species in CLOSE ASSOCIATION
  with EACH OTHER.

Ex (1) Predators AND prey sometimes co-evolve,
(2) Parasites AND their hosts often co-evolve,
(3) Herbivorous animals AND plants they feed on
also co-evolve, and lastly (4) Pollinators AND
pollinated flowering plants often co-evolve.
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(B) Convergent Evolution (result in ANALOGOUS
structures)

• Occurs when environment selects FOR similar
  phenotypes, even though ANCESTRAL types were
  QUITE different from each other.

Ex Great-White Shark AND Bottlenose Dolphin
(similar morphology for SWIMMING, but DIFFERENT
ANCESTRIES).
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(C) Divergent Evolution (result in HOMOLOGOUS
structures)

• 2 populations become more DISSIMILAR ? a
  response to geographical isolation (and
  ultimately, SPECIATION).

Ex American Porcupine AND Old World Porcupine
display HOMOLOGOUS features derived from a COMMON
ANCESTOR estimated 70 m.y.a.
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(1) Adaptive Radiation (i.e., DIVERGENT evolution)

• Related species EVOLVED from a single ancestral
  POPULATION.
• (Ex Darwins FINCHES of the Galapagos Islands
  have DIVERGED due to geographical isolation).

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(2) Artificial Selection (we can SPEED UP
divergent evolution)

• HUMAN influence on EVOLUTION of other species
  for various reasons (i.e., Selective Breeding).

• Examples include DOMESTICATION of dog breeds,
  LIVESTOCK, and agricultural CROPS.

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Extra Slides AND Answers for Critical Thinking
Questions
(1) You can conclude that the organism lived,
relatively unchanged, during the period during
which the two strata were deposited.
(2) A favorable trait that does not enhance the
reproductive success does not contribute to
evolution.
(3) Coevolution
(4) Organisms with a short generation time could
be modified more rapidly than those with a long
generation time. For example, a bacterium with a
generation time of one hour would have almost 9
million generations in 1,000 years, whereas
humans would have about 40 generations in the
same time span.
(5) There are many different environments and
many different demands on species. A species
adapted to one environment might fare poorly in a
different environment. Moreover, different types
of organisms are interrelated in complex ways.
For example, animals depend on plants for their
existence, and plants may depend on animals for
pollination.
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(6) The appendix can become infected, and if left
untreated, this condition is life-threatening.
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Revisiting Evolution

• The theory of evolution states that species
  change over time the mechanism for this change
  is natural selection.

• Fossils are one line of evidence for evolution,
  including the use of morphology, embryology, and
  DNA sequencing between species.

Assessing Prior Knowledge

• How does the DNA in an organism determine the
  structure and function of the proteins an
  organism produces?

• How could a change in DNA result in a change in
  the protein it manufactures?