Chapter 22: Decent with Modification: A Darwinian View of Life

1
Chapter 22Decent withModificationA
DarwinianView of Life
2
Can you read this?
If you cant read this then you really ought to
move to a new seat!
3
How about now?
If you cant read this then you really ought to
move to a new seat!
4
Important Point
If you are having trouble understanding lecture
material Try reading your text before
attending lectures. And take the time to read it
well!
5
Darwinian Evolution

• The material we cover in Bio 114 is very
  different from that covered in Bio 113,
  particularly in terms of the perspective and
  approach of those who engage in these different
  aspects of biology
• Its as though biology consists of two sciences,
  a reductionist science that seeks to emulate
  physics (113), and a philosophical science that
  is as interested in the subtleties of history as
  in the rigors of physical sciences (114)
• Its not that we will not be learning real
  science in Bio 114, but instead that our general
  approach toward learning will be somewhat
  different from that of Bio 113
• In Bio 113, basically, you sought to understand
  how a cell works here we will deal with such
  squishy topics as why it is the cells that we
  observe exist at all
• Keep an open mind and study hard and by the end
  of this term you will have gained an appreciation
  of the most important concept in biology
  Darwinian evolution

6
Charles Darwin
Darwin more popularized the idea of biological
evolution rather than inventing it
Evolution, in its most general sense, is simply
successive change that occurs over time
7
Darwinian Evolution

• Darwinism encompasses two distinct ideas
• The origin of biological diversity via evolution
• Natural selection as a mechanism of evolutionary
  change
• The process of evolution can be summarized in
  three sentences (talk.origins)
• Genes mutate
• Individuals are selected
• Populations evolve
• Major goals of this chapter
• Get a feeling for what it means for two organisms
  to be Evolutionarily Related
• Get a feeling for what is meant by Selection
  (a.k.a., Natural selection) and by Darwinian
  evolution
• Get a feeling for how we infer that organisms are
  evolutionarily related

8
Why Darwinism?

• Together the tenets of Darwinism serve as the
  foundation of our understanding of life
• Any time you generalize from one organism to
  another (e.g., from a fetal pig to a human) you
  are assuming evolutionary relationship
• Any time you speculate on the function of a
  biological structure, you are speculating on
  natural selection ( differential reproductive
  success)
• It is difficult to imagine biology as a coherent
  discipline absent Darwinism
• In fact, biology did not exist as a coherent
  discipline prior to the advent of Darwinism
• Nothing in biology makes sense except in light of
  evolution

9
1st Major Goal of Chapter 22

• Get a feeling for what it means for two organisms
  to be Evolutionarily Related
• Hint It means that the two organisms are related
  by Blood!
• Individuals from different species are just very
  distantly related cousins!
• This is true for all of the diversity of life
• Just as you and I are distantly related, only
  even more distantly related

10
Cladogram
A Cladogram is a graphed phylogeny--a depiction
of evolutionary relationships
11
Relatedness ofAll Cellular Organisms
Ultimately, if we go back far enough in time, all
living (i.e., extant) species may be collapsed
into a single, universal ancestral species (which
in all likelihood was a bacterium)
This and on the following pages are examples of
cladograms which show evolutionary relationships
of organisms we will meet again this quarter we
will not be excessively dwelling on them today
12
Relatedness of All Eukaryotes
To Darwin, the natural hierarchy of the Linnaean
scheme reflected the branching genealogy of the
tree of life, with organisms at the different
taxonomic levels related through descent from
common ancestors. p. 420, Campbell et al., 1999
13
Relatedness of All Plants
In biology, evolutionary change occurs within the
collective genotypes found within populations of
organisms
14
Relatedness of All Fungi
Evolution is a destabilizing process unless a
mechanism exists whereby destabilizing influences
are discarded in biology that stabilizing
influence we call natural selection
15
Relatedness of All Animals
16
2nd Major Goal of Chapter 22

• Get a feeling for what is meant by Selection
  (a.k.a., Natural selection) and by Darwinian
  evolution
• History of evolutionary thinking
• Mayrs logical summary of Darwinian evolution and
  natural selection
• Natural selection and adaptation
• Artificial selection
• Observation of selection (in particular, as a
  consequence of Man the modifier of
  environments)
• Evolutionary adaptation, an accumulation of
  inherited characteristics that enhance organisms
  ability to survive and reproduce in specific
  environments. p. 438, Campbell Reece (2005)

17
History of Evolutionary Thinking

• Aristotle, 384-322 B.C.E., Scala Naturae
  (biology)
• Natural Theology (understanding nature for the
  sake of understanding the glory of creators
  universe)
• Carolus Linnaeus, 1707-1778, Taxonomy (organizing
  organisms by phenotypic similarity) (biology)
• Georges Cuvier, 1769-1832, Catastrophism (e.g.,
  Noahs flood) (geology)
• James Hutton, 1729-1797, Gradualism (geology)
• Charles Lyell, 1797-1875, Uniformitarianism (same
  processes today as yesterday) (geology)
• Jean Baptiste Lamarck, 1744-1829, Adaptation
  (environment ? phenotypic change) (biology)
• Thomas Malthus, 1766-1834, Limits on Population
  Growth (biology economics)
• Charles Darwin, 1809-1882, Natural Selection
  (environment ? genotypic change) (biology)
• Alfred Russel Wallace, 1823-1913, Ditto

18
History of Evolutionary Thinking
However, note that "Evolution is not progress.
Populations simply adapt to their current
surroundings. They do not necessarily become
better in any absolute sense over time. A trait
or strategy that is successful at one time may be
unsuccessful at another." (Talk.Origins)
19
History of Evolutionary Thinking
Natural selection is simply the idea that when
organisms within environmentally limited
populations die, or don't make as many babies as
they otherwise could, they are dying or not
making as many babies non-randomly
20
Hutton vs. Lyell
In biology it is the making of babies that is
everything and we survive only to maximize our
reproductive output, thereby maximizing the
representation of our alleles within our
population
Cosistent with
Gradualism
and with
Uniformitarianism
21
Malthus Logic
From Malthus Darwin obtained the idea of limits
on population growth imposed by environments
Any species will eventually reach the limits of
its environment and then stop growing in numbers
22
Mayr Logic Darwinian Evolution

• Populations tend to have high reproductive
  potentials (?)
• Populations tend to be stable in size (?)
• Environments tend to possess limited resources
  (?)
• Therefore there exists a struggle for existence
• There exists phenotypic variation within
  populations
• Some phenotypic variation is heritable
• Within populations there is differential
  reproductive success
• That differential reproductive success is
  influenced by phenotypic differences between
  individuals

23
High Reproductive Potential
The intrinsic ability of populations to grow
typically exceeds their observed rate of growth
24
Mayr Darwinian Evolution

• Differential reproductive success leads to a
  decline in frequency of genotypes that underlie
  phenotypes that are less fit to the environment
• Differential reproductive success also results in
  a corresponding increase in frequency of
  genotypes that underlie phenotypes that are more
  fit to the environment
• This idea that differential reproductive success
  modifies genotypic frequencies in a manner that
  in principle may be predicted given knowledge of
  circumstances is know as Darwinian Evolution
• More specifically, differential reproductive
  success based on phenotypic differences is
  Natural Selection

25
An Alternative Perspective

• DNA (or RNA for some viruses) relatively stable
  information storage molecule ?
• Mutations changes in nucleotide sequence (new
  alleles) ?
• Change in Genotype (particularly if germ-line
  mutation) ?
• Can result in heritable changes in Phenotype
  (environment can also modify phenotype) giving
  rise to ?
• Variation among individuals making up populations
  (multiple alleles polymorphism variation not
  necessarily adaptive) ?
• Variation comes under the influence of the
  evolutionary forces of drift, selection, or
  migration ?
• Changes in Allele Frequencies ( evolution
  chapter 23) ?
• Changes in allele frequencies combined with
  reproductive isolation can result in Speciation
  (new species see chapter 24 macroevolution) ?
• Species either give rise to new species or are
  evolutionary dead ends (covered in chapter 25) ?
• In either case, all species eventually go extinct

26
An Alternative Perspective
Darwinism involves adaptation by populations to
local environments via the process of natural
selection
27
Summation of Darwinism

• Natural selection is differential success in
  reproduction
• this is an unequal ability of individuals to
  survive and reproduce
• note that the emphasis on reproduction, not
  survival
• Natural selection occurs through an interaction
  between the environment and the variability
  inherent among individual organisms making up a
  population
• The product of natural selection is the
  adaptation of populations of organisms to their
  environment
• Environments vary over space and over time, so an
  adaptation that is profitable in one environment
  may not be profitable in another
• Natural selection removes variation from
  populations it is not a source of variation
  (mutation is the ultimate source of genetic
  variation within populations)

28
Intra-Specific Variation (evolutionary potential)
We must distinguish between adaptations an
organism acquires by its own actions, and
inherited adaptations that evolve in a population
over many generations as a result of natural
selection. p. 444, Campbell et al., 1999
The former is physiological adaptation or
morphological adaptation while the latter is
evolutionary adaptation only the latter involves
changes in allele frequencies
29
Environment Impact on Phenotype
Change can also occur without adaptation, either
physiological or genetic here an organism is
being directly modified by its environment
30
Natural Selection Adaptation

• Cumulative adaptation is an important consequence
  specifically of natural selection
• Adaptations essentially are better fits between
  phenotypes and environments
• Natural selection serves to edit less-adaptive
  variation out of populations
• Fitness is defined in terms of reproductive
  success
• Variation that contributes to greater
  reproductive success, in the face of natural
  selection, tends to be retained within
  populations
• Note that I qualify the link between Adaptation
  Selection with the term Cumulative because it
  is mutation that gives rise to new alleles, not
  selection
• Natural selection, in particular, serves to
  increase the likelihood that adaptive mutations
  may be found in the same individuals

31
Natural Selection Adaptation
Evolution by natural selection is essentially an
interplay of an organisms genotype with an
organisms environment, whereby the product of
this evolution is a phenotype that allows the
possessing organisms to more closely fit their
environment
The resulting organisms reproductive success is
greater than it would have been had natural
selection not been operating
32
Artificial Selection Cruciforms
Artificial selection is evolutionary change where
environmental limits are purposefully defined by
man
Otherwise there exists no fundamental difference
between natural and artificial selection
Man can also impose inadvertent limits that also
result in evolutionary change
33
Artificial Selection Various Animals
Darwinism encompasses the idea that organisms
change with time, diverging from a common form
(i.e., they evolve)
34
Natural Selection Adaptation
35
More Adaptation
36
Industrial Melanism
Most prevalent morphotype prior to
industrialization
Can you see the moths?
Man, the modifier of environments! ( reason
trees are black)
37
Evolution of Insecticide Resistance
38
Evolution of Antibiotic Resistance
Natural selection occurs through an interaction
between the environment and the variability
inherent among the individual organisms making up
a population
39
Evolution Antivial Resistance
Natural selection is essentially a feedback loop
between a population and its environment, one
that is analogous (same idea, different
mechanism) as the feedback loops that we studied
in Chapter 18 (operons)
40
Building Adaptations
41
Evolution in Action Summary

• Antibiotic resistance in bacteria
• Antiviral resistance in viruses (including HIV)
• Insecticide resistance in insects
• Industrial Melanism
• Evolution of resistance to toxins and heavy
  metals (a consequence of toxic-waste dumping)
• Sickle cell anemia (and over dominance)
• Predator selection on guppies (earlier sexual
  development)
• Evolution of sex ratios (towards 11 ratio)
• Progression of cancer (and cancer resistance to
  chemotherapeutics)
• Evolution of pathogen virulence
• Etc.

42
Important Caveats

• Natural selection occurs through interactions
  between individual organisms and their
  environment, but individuals do not evolve
• Evolution can be measured only as changes in
  relative proportions of heritable variations in a
  population over a succession of generations
• Natural selection can amplify or diminish only
  heritable variations
• We must distinguish between adaptations an
  organism acquires by its own actions and
  inherited adaptations that evolve in a population
  over many generations as a result of natural
  selection
• It must also be emphasized that the specifics of
  natural selection are situational environmental
  factors vary from place to place and from time to
  time. An adaptation in one situation may be
  useless or even detrimental in different
  circumstances.
• from p. 437 of your text (6th edition)

43
Lamarckian vs. Darwinian Evolution
Darwinian evolution posits organism genetic
adaptation to environments, though it is actually
Lamarck who first conceived of such a concept
Difference? Darwin had a population emphasis
44
3rd Major Goal of Chapter 22

• Get a feeling for how we infer that organisms are
  evolutionarily related
• Answer 1 we can infer evolutionary distance via
  phenotypic similarity (but not always easily)
• Answer 2 we can infer evolutionary distance via
  genotypic similarity (easier but not always
  unambiguous)
• Answer 3 From the immense body of evidence
  available it is difficult, by Occams Razor, to
  conclude that organisms are not evolutionarily
  related

45
Occams Razor (through the ages)
46
Evolution of Artifacts
Isnt it obvious that these cars are
related? Isnt Relationship the Simplest
Explanation for Similarity? In biology,
information is carried by genes so relationship
is by decent
47
Homologies

• Homologies are similarities between organisms
  that are present due to common descent
• That is, the homology is also found in the common
  ancestor
• This is another way of saying that they (the
  organisms) share ancestry
• Sharing ancestry is another way of describing
  evolutionary relatedness
• Homologies tend to predict additional homologies
• For example, if an animal has feathers it
  probably also has wings
• Homologies form a layered pattern, with all life
  sharing the deepest layer and each smaller group
  adding fresh homologies to those they share with
  larger groups. p. 439, Campbell Reece, 2002

48
Homologies Vertebrate Forelimbs
Surely, the best way to construct the
infrastructure of a bats wing is not also the
best way to build a whales flipper. p. 439,
Campbell Reece, 2002
49
Homologies Vertebrate Embryos
A homologous structure is simply an anatomical
(i.e., structural) characteristic that serves as
a homology
Homologous structures are not necessarily useful
to a recipient organism
50
Modern Criteria for Homology

• Positional Homology Two structures are
  homologous if they have the same arrangements of
  similar parts
• Developmental Homology Two structures are
  homologous if they develop in the same way
• Genetic Homology Two structures are homologous
  if their development is controlled by the same or
  similar genes
• Phylogenic Homology Two structures are
  homologous if they appear to be inherited from a
  common ancestor
• From http//faculty.uca.edu/benw/biol4402/lectu
  re5/sld007.htm
• Also amino acid or nucleotide homologies

51
Complications
52
Molecular Homologies
53
Skull Homologies
54
Human-Bonobo Homologies
55
Vestigial Structures
56
Vestigial Structures
Vestigial structures are a kind of homology, the
persistence of a feature, though one which is no
longer (terribly) useful to its owner
57
Paleo Homology (whale legs)
A homology, one shared with other tetrapods, and
one that is not vestigial
58
More on Whale Evolution
A structure that is expensive to make or to
sustain, but which makes little positive impact
on survival or reproductive success will not be
selected for (indeed, may be selected against)
and therefore ultimately may be lost via
evolution (i.e., via natural selection or via
genetic drift)
59
Developmental Error
The genes for tail formation presumably are still
with us, just not normally expressed (that is,
they are vestigial).
60
Analogies
Analogies do not tend to predict homologies,
e.g., if an animal has wings it does not
necessarily also have feathers
marsupial
placental
Analogies, however, can predict related
structural similarities, e.g., wings flying
lightweight bodies
61
Convergent Evolution
Analogies are products of convergent evolution
62
Biogeography

• Biogeography is the study of the real-world
  distribution of organisms.
• Organisms are limited in their ability to
  disperse
• As a consequence, evolutionary lineages are more
  likely to evolve locally (or regionally) rather
  than globally
• If you were inferring the relatedness of three
  species, two of which were found in the same
  region, the third on a different continent, you
  would predict a closer relatedness of the first
  two
• Homologies often correlate with geography (e.g.,
  old-world vs. new-world monkeys)

63
Biogeography
Environments are not necessarily populated by the
organisms best suited to those environments
organisms instead are typically limited in their
ability to traverse geographical barriers
including great distances
Local novel environments tend to be first
populated by less well-adapted organisms from
nearby given isolation, populations become
better adapted with time
64
Darwin Round the World!
Many of Darwins inferences were in terms of
biogeography
65
The Fossil Record
66
More Fossils (Pretty)
67
(No Transcript)
68
The End