Nothing in biology makes sense except in the light of evolution. – Theodosius Dobzhansky

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Evolution
Nothing in biology makes sense except in the
light of evolution. Theodosius Dobzhansky
Charles Darwin in later years
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What is Evolution?
The kind were talking about is sometimes called
organic evolution to distinguish it from
non-biological changes over time.
Working definition Evolution is the progressive
change in populations over time. NOT SPECIES, NOT
INDIVIDUALS
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Evolution Holds a Unique Place in Biology
Other disciplines ask how?
Evolutionary biology asks why?
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Evolutions Core Principles
Natural selection.
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Evolutions Core Principles
Common descent with modification.
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Evolutionary Time Scales
Macroevolution Long time scale events that
create and eliminate species.
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Evolutionary Time Scales
Microevolution Short time scale events
(generation-to-generation) that change the
genotypes and phenotypes of populations.
Well begin our more intensive look at evolution
with microevolution.
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Darwins Voyage of Discovery
A reconstruction of the HMS Beagle sailing off
Patagonia.
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The Voyage of the Beagle
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Darwins Ideas Did Not Develop in a Vacuum
Contributors to Darwins thinking included
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Darwins Ideas Did Not Develop in a Vacuum
Contributors to Darwins thinking included
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Alfred Russel Wallace Independently Drew the Same
Conclusions as Darwin
Papers from Wallace and Darwin were jointly
presented (with little impact) to the Linnaean
Society in 1858.
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Haeckel ontogeny recapitulates phylogeny

• Thomas Hunt Morgan Darwins bulldog

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Darwins Observations and Inferences Organized by
Ernst Mayr
Observation 1 Left unchecked, the number of
organisms of each species will increase
exponentially, generation to generation.
Observation 2 In nature, populations tend to
remain stable in size.
Observation 3 Environmental resources are
limited.
Inference 1 Production of more individuals than
can be supported by the environment leads to a
struggle for existence among individuals, with
only a fraction of offspring surviving in each
generation.
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Darwins Observations and Inferences
Observation 4 Individuals of a population vary
extensively in their characteristics with no two
individuals being exactly alike.
Observation 5 Much of this variation between
individuals is heritable.
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Darwins Observations and Inferences
Inference 2 Survival in the struggle for
existence is not random, but depends in part on
the heritable characteristics of individuals.
Individuals who inherit characteristics most fit
for their environment are likely to leave more
offspring than less fit individuals.
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Darwins Observations and Inferences
Inference 3 The unequal ability of individuals
to survive and reproduce leads to a gradual
change in a population, with favorable
characteristics accumulating over generations
(natural selection).
Taken together, these three inferences are a
statement of Darwins Theory of Evolution.
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The Weak Link of Genetics and the Modern Synthesis
A major problem in Darwins theory was the lack
of a mechanism to explain natural selection. (No
mitosis, meiosis, replication, chromosomes, laws
of inheritance)
How could favorable variations be transmitted to
later generations?
With the rediscovery of Mendels work and its
vast extension in the first half of the 20th
century, the missing link in evolutionary theory
was forged.
Darwinian theory supported by genetics is known
as the modern synthesis.
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Discomfort With Evolution
The upheaval surrounding evolution began with
publication of On the Origin of Species and
continues nearly 150 years later.
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Discomfort With Evolution
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Discomfort With Evolution
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Discomfort With Evolution
Two of many arguments made against evolution are
Evolution is only a theory.
No ones ever seen evolution.
The first point is true, but misses the meaning
of scientific theory, and the second point is
easily countered.
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Evidence for Evolution The Fossil Record
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Evidence for Evolution - Comparative
Morphology Homologous structures
Why use the same skeletal plan for these very
different appendages?
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Evidence for Evolution - Comparative Embryology
Why do embryos of different animals pass through
a similar developmental stage?
Recent discoveries of the conservation of
molecular mechanisms of development are even more
compelling.
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Evidence of Evolution Conservation and
Diversification at the Molecular Level
Why should different organism possess related
genes?
Why does the degree of relationship of genes
match their degree of relationship established by
other methods?
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Evidence for Evolution Evolution Observed
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Evidence for Evolution Evolution Observed
Evolution of drug-resistance in HIV
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Modes of Selection
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Special Examples

• Kin Selection relative fitness includes fitness
  of close relatives
• Artificial selection farming/animal breeding
• Sexual selection based on mating
• Convergent evolution different ancestor common
  lifestyle (analogous structures result)
• Divergent evolution common ancestor different
  lifestyle (homologous structures result)
• Parallel evolution evolving in the same pattern
• Coevolution two evolving each other

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Speciation

• Steps in the process
• Subdivision of the population
• Evolution of each subpopulation in independent
  directions
• Change in population that reproductively isolates
  the population from the other.
• Return to same setting and no longer can members
  of the two populations mate.

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Speciation

• Allopatric Geographical separation leads to
  initial subdivision of the population.
• Rivers, volcanoes, earthquakes, roads, train
  lines, etc..

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Sympatric speciation

• Sympatric Isolation of populations occurs while
  organisms have physical contact with each other.

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More sympatric

• Apple maggot flies

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Temporal/Sympatric speciation
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Reproductive Isolation

• Prezygotic vs. Postzygotic
• Needed for speciation Organisms can look
  somewhat different and still be one species if
  this does not occur.
• Organisms can look very much alike, but be two
  species if this occurs.
• The idea is that eventually diversity will build
  up in the populations independently and thus
  would eventually look different.

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Many Intrinsic Reproductive Isolating Mechanisms
Drive Speciation
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Behavioral Isolation Mechanisms
Courtship rituals, like these, are critical for
mating within a species, but ineffective for
attracting members of other species.
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Many Intrinsic Reproductive Isolating Mechanisms
Drive Speciation
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Many Intrinsic Reproductive Isolating Mechanisms
Drive Speciation
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Many Intrinsic Reproductive Isolating Mechanisms
Drive Speciation
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Speciation Dynamics - Gradualism or Punctuated
Equilibrium?
Punctuated equilibrium appears to be a more
accurate view of speciation dynamics. long
period lacking speciation where variation builds
up followed by some dramatic change in the
environment that leads to a struggle for survival
and lots of speciation and microevolution.
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Evolution possibilities

• Convergent evolution leads to analogous
  structures. (same function/different ancestry)

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Parallel evolution vs. Coevolution

• A divergent B convergent C. parallel

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Divergent evolution

• Divergent evolution leads to homologous
  structures. (same ancestry/different function)

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Coevolution

• Yucca moth and Yucca flower

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Does coadaptation mean coevolution?