Principles of Evolution

1
Principles of Evolution

• Chapter 6 Evidence of Evolution
• James F. Thompson, Ph.D., MT(ASCP)

2
Recall Darwins Evidence

• The Origin of Species By Means of Natural
  Selection or the Preservation of Favoured Races
  in the Struggle for Life, documents that fact
  that evolution has occurred
• gives examples of artificial and natural
  selection to explain the mechanism of evolution
• includes considerable evidence from comparative
  anatomy and comparative embryology
• relies very little on the fossil record, a record
  still quite meager in the 1850s

3
Darwin Artificial Selection
4
Darwin Artificial Selection
5
Darwin Artificial Selection
Darwin was a recognized expert on pigeon breeds.
6
Evidence of Organismal Change
Several Hundred Breeds Recognized
7
Darwins Pigeons
Darwins studies of pigeon breeds included a
tentative phylogeny
8
Darwins Pigeons
Darwins studies of pigeon breeds included
detailed comparative anatomy
mandibles
However, Darwin did not mention the Galapagos
finches in The Origin of Species.
9
Comparative Anatomy

• Edward Tyson (16501708) is regarded as the
  founder of comparative anatomy.
• In 1680, he demonstrated that porpoises are
  mammals.
• In 1698, he dissected a chimpanzee and the result
  was the book, Orang-Outang, sive Homo Sylvestris
  or, the Anatomy of a Pygmie Compared with that of
  a Monkey, an Ape, and a Man.
• He concluded that the chimpanzee has more in
  common with man than with monkeys, particularly
  with respect to the brain.

10
Thomas Henry Huxley

• Frontispiece to Huxley's Evidence as to Man's
  Place in Nature (1863), comparing the skeletons
  of various apes to that of man.

11
Macroevolution The Transition From Reptile to
Bird Microraptor gui
12
Microevolutionary Change in Soapberry Bugs
A shortened beak is an adaptation to an
introduced food source.
13
Micro-evolutionary Change in DarwinsFinches
Body size and beak characteristics vary in
response to El nino induced droughts.
The drought changes the plant community and the
birds respond by adapting to new proportions of
seeds of differing size and hardness (bigger
and harder during drought.)
14
Comparative Embryology

• Aristotle Preformation, Epigenesis, Pangenesis
• Renaissance (human/medical) anatomists continued
  to collect data based on the ancient concepts
• Leonardo Da Vinci, William Harvey, Marcello
  Malpighi, many others, especially the Italians
• Christian Pander, Heinrich Rathke, and Karl Ernst
  von Baer founded modern embryology in the 1820s
  in Germany
• Advances in microsopes and stains and the
  establishment of the Cell Theory of Life
  contributed to the progress

15
Comparative Embryology

• Christian Pander discovered the three primary
  germ layers ectoderm, endoderm, and mesoderm
• Pander also discovered the reciprocal regulatory
  tissue interactions among embryonic cells we now
  call Induction.

16
Comparative Embryology

• Heinrich Rathke described for the first time the
  vertebrate pharyngeal/branchial pouches/arches,
  which become the gill apparatus of fish but
  become the mammalian jaws and ears, and
  contribute to the formation of the vertebrate
  skull, and the origin of the vertebrate
  reproductive, excretory, and respiratory systems.

17
Comparative Embryology

• Karl Ernst von Baer extended Pander's studies of
  the chick embryo.
• von Baer discovered the notochord, the rod of
  dorsal most mesoderm that separates the embryo
  into right and left halves and which instructs
  the ectoderm above it to become the nervous
  system.
• He also discovered the mammalian egg.

18
von Baer's Laws

• The general features of a large group of animals
  appear earlier in development than do the
  specialized features of a smaller group.
• All developing vertebrates appear very similar
  shortly after gastrulation.
• It is only later in development that the special
  features of class, order, and finally species
  emerge.
• All vertebrate embryos have gill arches,
  notochords, spinal cords, and primitive kidneys.
• Less general characters are developed from the
  more general, until finally the most specialized
  appear.
• All vertebrates initially have the same type of
  skin.
• Only later does the skin develop fish scales,
  reptilian scales, bird feathers, or the hair,
  claws, and nails of mammals.
• Similarly, the early development of the limb is
  essentially the same in all vertebrates.
• Only later do the differences between legs,
  wings, and arms become apparent.

19
von Baer's Laws

• The embryo of a given species, instead of passing
  through the adult stages of lower animals,
  departs more and more from them.
• The visceral clefts of embryonic birds and
  mammals do not resemble the gill slits of adult
  fish in detail.
• Rather, they resemble the visceral clefts of
  embryonic fish and other embryonic vertebrates.
• Whereas fish preserve and elaborate these clefts
  into true gill slits, mammals convert them into
  structures such as the eustachian tubes (between
  the ear and mouth).
• Therefore, the early embryo of a higher animal is
  never like a lower animal, but only like its
  early embryo.
• Human embryos never pass through a stage
  equivalent to an adult fish or bird.
• Rather, human embryos initially share
  characteristics in common with fish and avian
  embryos.
• Later, the mammalian and other embryos diverge,
  none of them passing through the stages of the
  others.

20
Comparative Embryology Darwin

• Darwin did some comparative embryology himself.
• Darwins drawing (left) compares human and cat
  embryos
• Photo (right) compares human and dog for
  comparison to confirm Darwins accuracy

21
Ernst Haeckel

• Recall Haeckel who developed the controversial
  recapitulation theory ("ontogeny recapitulates
  phylogeny") claiming that development, or
  ontogeny, parallels and summarizes its species'
  entire evolutionary development, or phylogeny,
  based on continuing embryological studies.

22
Comparative Embryology

• Structure unfolds during development in a
  conservative fashion.
• Structural innovations usually appear at the end
  of development proceses, not the beginning.
• This minimizes the disruption of potentially
  ancient and well established regulatory
  sequences.
• New character traits form by remodeling rather
  than by new construction without a foundation.

23
beak limb buds
digits
heart
feathers
24
Homology and Analogy

• Darwins contemporary, the comparative anatomist
  and paleontologist, Richard Owen, coined the
  terms homology and analogy (and Dinosauria).
• To Owen, homologies indicated that organisms were
  created following a common (Divine/Vitalist) plan
  or archetype.

25
Homology and Analogy

• Homology Any similarity between phenotypic
  characters that is due to their shared ancestry.
  Homologous structures may retain the function
  they served in the common ancestor or they may
  evolve to fulfill different functions.
• Analogy Any phenotypic characters that perform
  the same or similar function by a similar
  mechanism but evolved separately.

26
Developmental Homology

• Developmental Homology A related concept
  meaning that structures arose from the same
  tissue in embryonal development the ovaries and
  clitoris of female humans and the testes and
  penis of male humans are homologous in this
  sense.

27
Developmental Homologies
All exhibit external head, tail, limb buds,
pharyngeal pouches, as well as internal
homologies.
28
Homologies are Everywhere!

• The leaves of vascular plants (oak, gingko, pine)
  are homologous.

29
Homologies are Everywhere!

• The wings of insects (dragonfly, butterfly,
  cockroach) are homologous.

30
Classic Structural Homologies
Determining that Phenotypic Traits are
Homologous Allows Scientists to Build Phylogenies
31
Classic Structural Homologies
The vertebrate forelimbs have the same basic bone
design one long bone attached to two other long
bones attached to a forefoot with many carpals
attached to five or fewer digits. The vertebrate
hindlimb offers similar evidence of homology.
32
Different Functions but Similar Underlying
Forelimb Anatomy

• Homology of forelimbs of bat, mole, and dugong.
• Each limb performs a different function-flight,
  digging, and swimming, respectively-and all are
  superficially different, but all three share a
  common, underlying anatomical plan.

33
Classic Structural Homologies

• Several animals, including pigs, cattle, deer,
  and dogs have reduced, nonfunctional digits,
  referred to as dewclaws.
• The foot of the pig has lost digit 1 completely,
  digits 2 and 5 have been greatly reduced, and
  only digits 3 and 4 support the body.

34
Classic Structural Homologies

• These are best explained if there was a common
  ancestor that at one time had more functional
  digits.
• Thus pigs, cattle, deer, and dogs can be thought
  to have a common ancestor and are homologous to
  each other (although distantly)

35
Classic Structural Homologies

• The dog retains four functional digits and digit
  1 has become a dewclaw

36
Classic Structural Homologies

• The number of digits was variable in the earliest
  fossil amphibians but pentadactyly became the
  standard for all later vertebrates, though there
  have been many reductions in number and a much
  fewer increases in certain finned reptiles.

37
Diversity of Type, Unity of Pattern

• Parts may be similar in ancestry, function,
  and/or appearance.
• Respectively, these are defined as homology,
  analogy, or homoplasy.
• Although the vertebrate species differ, the
  underlying pattern of the forelimb is
  fundamentally the same.

38
Diversity of Type, Unity of Pattern

• Although the vertebrate species differ, the
  underlying pattern of the forelimb is
  fundamentally the same.
• Note again that the major changes come in the
  number of phalanges and thelength and number of
  bones making up the phalanges

39
Homologies

• Humans and all other apes have chests that are
  broader than they are deep, with the shoulder
  blades flat in back, with associated differences
  in shoulder muscle attachments, an adaptation to
  brachiation.
• Monkeys and most other tetrapods walk
  quadrupedally and have narrow, deep chests with
  shoulder blades on the sides.
• This homology, the anatomical and behavioral
  adaptations for brachiation, is a shared derived
  character for the apes.

40
Homologies

• Homologous structures may be adapted for
  different roles in which case their structure may
  vary considerably. Consider mammalian incisors
  and canines.

41
Structural Homologies
orchid flower structure
homologous
From Darwin (1862)
42
Structural Homologies

• The Eukaryotic Cell
• Nucleus
• mitosis
• meiosis
• DNA supercoiling with histones and higher levels
• Cytoplasm
• all cellular organelles
• most central cellular biochemical pathways
• Plasma membrane
• phospholipid bilayer
• cholesterol present

43
A Deep Homology The Genetic Code
This is one of the most powerful of
all homologies, as it links all living
organisms on Earth to a common ancestor!
A few microbes have a few differences.
44
Protein Homologies

• The gene that codes for the protein hormone
  insulin is homologous in humans and other
  mammals the similar DNA sequences descended from
  a common ancestral gene sequence.
• Human insulin (right) and pig insulin (left),
  showing their one amino acid difference

45
Behavioral Homologies

• Birds, crocodiles, and mammals provide parental
  care to their offspring
• This behavior was inherited from a common
  ancestor and is certainly homologous for birds
  and crocodilians
• It is less certain their common ancestor with the
  mammals exhibited a similar degree of parental
  care.

46
Homology A Genetic Flaw That Humans Share With
Chimpanzees
Charcot-Marie-Tooth Disease
PMP-22 peripheral myelin protein 22
47
Analogies

• Analogy Any phenotypic characters present in
  different taxa which perform the same or a
  similar function by a similar mechanism but which
  evolved separately.
• The structural carbohydrate chitin in fungal cell
  wall and in arthropod exoskeletons

48
Analogies
Traits their common ancestor lacked.
Mosasaur
shark killer whale
hydrodynamic body forms
wings
49
Analogies
Legs
50
Analogies

• Thylacosmilus is a marsupial sabre-tooth cat
• Smilodon is a placental saber-tooth cat.

51
Analogies
Camera-type Eyes
52
Analogy Oxygen-Binding Proteins

• Hemoglobin combines iron heme groups and globin
  proteins, red pigment found in vertebrate
  erythrocytes
• Myoglobin combines iron heme groups and globin
  proteins, red pigment found in vertebrate muscle
  tissues
• Hemocyanin combines copper prosthetic groups and
  globin proteins, blue pigment found in arthropod
  and mollusc blood plasma
• Hemerythrin combines iron-containing non-heme
  globin proteins, pink/violet vs colorless pigment
  found in some marine invertebrate blood plasma
• Chlorocruorin combines iron heme groups and
  globin proteins, red vs green pigment found in
  many annelids
• Vanabins (aka vanadium chromagens) combine the
  rare metal vanadium in prosthetic groups and
  globin proteins, colorless molecules found in sea
  squirts blood plasma
• Erythrocruorin is a giant free-floating blood
  protein containing many dozens possibly
  hundreds of iron- and heme-bearing protein
  subunits bound together into a single protein
  complex with a molecular mass greater than 3.5
  million daltons Found in many annelids, including
  earthworms.
• Pinnaglobin is a brown manganese-based porphyrin
  protein only found in the mollusc Pinna squamosa.
• Leghemoglobin combines iron heme groups and
  globin proteins, colorless compound found in
  leguminous plants, such as alfalfa or soybeans.

53
Homoplasy

• Homoplasy is the logical opposite of homology.
• Homoplasy is the structural similarity between
  two traits in two species without phyletic
  continuity.
• Even though the traits are similar, the common
  ancestor of species A and B did not present the
  trait.
• There are three different types of homoplasy
  convergence, parallelism, and reversal.

54
Homoplasy

• Convergence is the evolution of similar traits in
  response to similar adaptive pressures, but not
  to similar genes and developmental processes
• An example of convergence is found in the
  electroreception of mormyrids (African weak
  electric fish) and gymnotoids (South American
  electric eels) while the organs responsible for
  this perceptual capacity are similar, they are
  not derived from a common ancestor.

55
Convergence of Design
Groups of animals often adapt to habitats that
differ from those of most other members of their
group. Common function alone is insufficient to
explain all aspects of design. Despite current
similar habitats, each design carries
evolutionary features of the past into the
present.

• Most birds fly, but some, such as ostriches,
  cannot, and live exclusively on land others,
  such as penguins, live much of their lives in
  water. Most mammals are terrestrial, but some fly
  (bats) and others live exclusively in water
  (whales, dolphins). Flying fishes take to the
  air. As species from different groups enter
  similar habitats, they experience similar
  biological demands. Convergence to similar
  habitats, in part, accounts for the sleek bodies
  and fins or flippers of tuna and dolphins,
  because similar functions (analogy) are served by
  similar parts under similar conditions. Yet tuna
  and dolphins come from different ancestries and
  are still fishes and mammals, respectively.

56
Convergence Ecological Equivalents
57
Ecological Equivalentswithout Convergence
Pileated Woodpecker ? And Woodpecker Finch ?
Madagascar Aye-Aye
58
Mimicry/Analogy/Convergence
59
Mimicry/Analogy/Convergence
60
Mimicry/Analogy/Convergence

• Pollination in the Bee orchid (Ophrys apifera) is
  enhanced by reproductive mimicry and the
  pheremones that attract specific male bumblebees.

61
Homoplasy
An extinct South American Litoptern

• Parallelism occurs in closely related taxa, and
  is defined as the independent development of a
  descendant character that is not present on a
  common ancestor.
• Parallelism occurs when two taxa develop the same
  character after evolutionary divergence since
  the trait is absent in a common ancestor, but
  present in both descendant species, it is
  probable that the developmental genetics that
  produces the structures in the different taxa is
  the same, which means it was inherited from the
  common ancestor.
• Thus, there is homology between the developmental
  and genetic materials, but not on the final
  structure.
• (Also ecological equivalents.)

camel
62
Homoplasy
Snake eyes
python
monitor

• Reversals are instances of homoplasy in which a
  character appears, subsequently disappears, and
  later reappears among the descendants in one
  lineage.

blind lizard
63
Homology?Homoplasy?Analogy
Homoplasy (convergence)
64
The Pandas Thumb?

• The panda has five digits like most mammals
  however, opposing these is another digit, a
  thumb, which is actually not a thumb at all
  but an enlarged wrist bone.

65
Homology and Model Organisms
66
Human (Intelligent) Design

• Machine functions vary and machine designs vary
  accordingly.
• Unlike biological organisms, human designed and
  built machines show no correspondence of parts
  from planes (flight), to mining machines
  (burrowing), or to boats (swimming).

67
Morphological Series

• Comparative evidence allows systematists to
  collect taxa into nested clusters
• Introduction of new shared derived characters can
  help establish both grades and clades
• Availability of fossil specimens improves the
  understanding of common ancestors
• Related taxa can be organized into morphological
  series for explanatory purposes (grades and
  clades)

68
Trilobite Phylogeny
69
Morphological SeriesEvolution of Jaws

• Vertebrate jaws evolved from the front set of
  gill arches of jawless ancestors.

placoderms
ostradocerms
70
Morphological SeriesEvolution of Limbs from Fins

• Note that the bones of the fish hip and shoulder
  correspond to bones in this early tetrapod
  (amphibian).
• Here, the morphological series carries from one
  type of vertebrate (fish) to another (amphibian),
  and from one environment (water) to another
  (land).

71
Evolution of Horses
Orthogenesis
O.C. Marsh 1879
72
Evolution of Horses
Bruce McFadden 2005
J.W. Gidley 1907
73
Evolution of Horses
Another Modern Horse Phylogeny
74
This morphological series illustrates the
correspondence between parts (feet, teeth, skull)
and their modifications.
75
Transitional Fossils Documenting the Evolution of
Birds from Dinosaurs
Dromaeosaurus (with feathers?)
Archaeopteryx
Sinosauropterxyx
76
Transitional Fossils Documenting the Evolution of
Whales from Legged Ancestors
Reported 2001
Rodhocetus
Reported 1994
Reported 1990
77
Hominoid Morphological Series
Well save our discussion of the morphological
series leading to Homo sapiens until Chapters 14
15
78
Vestigial Features

• The term Vestigial Feature refers to behaviors,
  anatomical structures, physiological processes,
  biochemical pathways or gene sequences
  (pseudogenes and junk DNA), which have lost most
  or all of their original adaptive function, an
  adaptive function which may still be observed in
  the corresponding homologous feature in some
  related species or other taxon.
• Some of these vestigial features disappear early
  in embryonic development, but others are retained
  in adulthood.
• Vestigial Features typically appear to be in a
  degenerate, atrophied, or rudimentary condition,
  and tend to be much more variable than similar
  parts.
• Although largely or entirely functionless,
  vestigial features may retain lesser functions or
  develop minor new ones.

79
Developmental Vestigial Features
80
Developmental Vestigial Features
Chick embryo
fifth digit
foot
wing
No remnant persists in the adult
81
Vestigial Features

• Whales evolved from terrestrial tetrapods. But in
  whales, the hips and hindlimbs are reduced to
  small bones with no function.
• Snakes evolved from lizards with four legs. But
  in primitive snakes (e.g., pythons), the remnants
  of hindlimbs persist (forelimbs are absent).

82
Vestigial Features
Eyes Wings
Hind limbs
83
Vestigial Features
Hoatzin chick wing claws adaptive
Emu adult wing claws vestigial
84
Vestigial Features
telson (tail)
85
Vestigial Features
Many Taraxacum species produce seeds asexually by
apomixis, where the seeds are produced without
pollination.
86
Vestigial Features
Hieracium aurantiacum (orange hawkweed)
Antennaria dioica (mountain everlasting)
87
Vestigial Wings?
Galapagos Cormorant yes
Ostrich no
Kiwi yes
Penguin no
88
Vestigial Features

• The human appendix is a vestigial structure,
  reduced from the cecum of primate ancestors,
  where it was involved in digestion of significant
  amounts of plant material.

rabbit cecum
89
Human Vestigial Features
(15,000 year old woman)
vermiform appendix
wisdom teeth 3rd molars
muscles to move the external ear
coccyx
arrector pili muscle
90
Atavistic Features

• Extra toes in modern horses.
• (a) Modern horses have only one enlarged digit on
  each foot, a single toe. The one toe evolved from
  ancestors with three or four toes.
• During the course of their evolution, the
  peripheral toesIV, II, Iwere lost and the
  central toeIIIemphasized. (b,c)
• On rare occasions, however, these lost toes or
  their remnants reappear, testifying to the
  lingering presence of the underlying ancestral
  developmental pattern.
• (d) On rare occasion, a modern horse, such as the
  one illustrated, is born with additional toes.
  Such toe remnants in modern horses apparently
  represent the partial reemergence of an ancient
  ancestral pattern.

91
Atavistic Features

• In 2006, a bottlenose dolphin with palm-sized
  fins near its tail was found in Japan.
• The extra set of fins are atavistic hind limbs.

92
Atavistic Features

• Supernumerary nipples. (Third and fourth nipple
  of male scandinavian).
• A - regular birthmark.
• B - regular nipple.
• C - supernumerary nipple

Another male
93
Atavistic Features

• A radiogram of the sacral region of a six-year
  old girl with an atavistic tail.
• The tail was perfectly midline and protruded form
  the lower back as a soft appendage.
• The five normal sacral vertebrae are indicated in
  light blue and numbered the three coccygeal tail
  vertebrae are indicated in light yellow.
• The entire coccyx (usually three or four tiny
  fused vertebrae) is normally the same size as the
  fifth sacral vertebrae.

94
Atavistic Features

• A well-developed tail is characteristic of the
  human embryo in the second month.
• Ususally during the third month the tail
  regresses and disappears as an anatomic external
  feature.
• Occasionally the tail persists and grows with the
  rest of the body.
• Tails as long as 23 cm have been reported.

95
From Homology to Phylogeny

• Homologous traits can be grouped into series
• Homologous traits can include adaptive traits,
  maladaptive traits, vestigial features and
  atavisms
• All homologous traits can be of potential use in
  deriving phylogenetic trees
• However, care must be taken to avoid using
  analogous traits by mistake
• Finally, homologous traits are excellent evidence
  that evolution has, in fact, occurred!

96
The Geological Record Evidence for Evolution
Weve already looked at the Fossil Record as
Evidence that Evolution Has Occurred
97
Distributional Evidence for Evolution

• "The most wonderful mystery of life may well be
  the means by which it created so much diversity
  from so little physical matter.  The biosphere,
  all organisms combined, makes up only about one
  part in ten billion of the earths mass.  It is
  sparsely distributed through a kilometer of soil,
  water, and air Yet life has divided into
  millions of species, the fundamental units, each
  playing a unique role in relationship to the
  whole."  - E.O.Wilson The Diversity of Life
  (1992)

98
Distributional Evidence for Evolution

• Biogeography is the study of the spatial
  distribution of species (and higher taxa) and
  their ecological communities through time.
• Biogeography organizes information about where
  organisms live, how they arrived there, and their
  evolution and ecology.
• The patterns of species distribution are usually
  explained through a combination of principles
• evolution (acaptation, speciation, extinction,
  ecology, etc.)
• geoclimate (continental drift, glaciation,
  fluctuations in sea level, weather, wind and
  water movements, etc.)
• geography (surface topography, soil composition,
  energy and resource availability, etc.)

99
Alfred Russel Wallaceis the Father of
Biogeography

• As a young man, Wallace studied the distributions
  of living organisms in the Malay Archipeligo
  where he lived for several years.
• His classic works, the two-volume work, The
  Geographical Distribution of Animals (1876) and
  Island Life (1880 ) would serve as the definitive
  texts on biogeography for the next 80 years.

100
Wallaces Line

• Wallace propssed six biogeographic realms for the
  earth, based primarily on animal distributions.
• He was most familiar with South East Asia where
  we still honor him with Wallaces Line which
  marks the boundary between Australian and Asian
  fauna.

101
Biogeographic Realms

• Below is a modern version of Wallaces six
  biogeographic realms based on the number of
  mammalian families.

Endemic families are those found in only the one
location (realm).
102
Eight Modern Biogeographic Realms
Wallaces six and
7
7
Eighteen biomes are mapped within realms in this
modern global map.
8
103
Darwin and Biogeography

• In The Origin of Species Darwin wrote of centers
  of creation, which later came to be known as
  centers of origin for various taxa.
• A center of origin is a proposed location, based
  on fossil or modern distribution evidence, for
  the home of the oldest common ancestor of a
  taxonomic group
• A related concept is center of diversity, a
  region where the greatest proportion of members
  of the taxanomic group are present.
• A center of origin and a center of diversity are
  often the same location, or not far from one
  another.

104
Centers of Origin and Dispersal

• These centers remain useful concepts.
• However, from the 1860s to the 1960s they
  sometimes confused issues because scientists
  assumed the continents had always been in the
  same locations throughout geologic time.
• If so, then terrestrial organisms were
  distributed across the globe in ways that were
  difficult to explain.
• Hypotheses for methods of long distance dispersal
  were required.

105
Examples of Centers of Origin
106
Land Bridges

• Connections between geographic areas allow for or
  restrict dispersal of plants and animals. (a)
  Corridors allow for the relatively uninterrupted
  spread of organisms.
• The doubleheaded arrows indicate such open
  expanses across Eurasia and North America.

corridor
corridor
107
Land Bridges

• Connections between geographic areas allow for or
  restrict dispersal of plants and animals. (a)
  Filter bridges permit selective transit of
  organisms that pass, either because of
  inhospitable climate or ecological obstruction.
• One major selective filter has been across the
  Bering Strait another is in the Middle East,
  restricting reptile species.

filter bridge
filter bridge
108
Land Bridges

• (b) Filter bridges between North and South
  America occur in the narrow land connection
  between these continents.
• Some species have crossed this filter, but others
  have not.

filter bridge
109
Land Bridges

• If continents do not move, however, then how do
  we explain the bridge to disperse marsupials
  between Australia and the New World or alligators
  and dogwoods between the Southeast United States
  and Southeast China?

alligators and dogwoods
marsupials
There were dozens, if not hundreds, of equally
mystifying distributions known!
110
Methods of Long Distance Dispersal

• You can read a classic paper on the subject
• Mammals and Land Bridges by George Gaylord
  Simpson (1940)
• www.wku.edu/smithch/biogeog/SIMP940B.htm
• Recall that Simpson was the paleontologist among
  the founders of The Modern Synthesis of Evolution

111
Continental Drift

• Alfred Wegener (1880 1930), a German
  meteorologist, proposed continental drift in 1912
  based on fossil and mineral distributions and
  continental coast lines
• He proposed that all the continents were once
  joined in a single landmass, which he called
  Pangaea.
• Plate Tectonics was not accepted as the
  explanatory theory until the 1960s.

112
Continental Drift
Laurasia Gondwana
Pangaea

• Changing continental positions through most of
  the Phanerozoic era. Time, in millions of years,
  is approximate.

113
Plate Tectonics

• Plate tectonics describes the large scale motions
  of Earth's lithosphere.
• The theory encompasses the older concepts of
  continental drift, developed during the first
  half of the 20th century, and seafloor spreading,
  understood during the 1960s.

114
Plate Tectonics

• The outermost part of the Earth's interior is
  made up of two layers above is the lithosphere,
  comprising the crust and the rigid uppermost part
  of the mantle.
• Below the lithosphere lies the asthenosphere.
• Although solid, the asthenosphere has relatively
  low viscosity and can flow like a liquid on
  geological time scales.
• The deeper mantle below the asthenosphere is more
  rigid again due to the higher pressure.

115
Plate Tectonics

• The lithosphere is broken up into what are called
  tectonic plates  in the case of Earth, there are
  seven major and many minor plates.
• The lithospheric plates ride on the
  asthenosphere.
• Earthquakes, volcanic activity,
  mountain-building, and oceanic trench formation
  occur along plate boundaries.

116
Tectonic Plates
117
Continental Drift

• Léon Croizat (1894 1982), an Italian biologist,
  whose career included time in the US (1936-47)
  and later in Venezuela, also proposed continental
  drift, more or less independently, based on
  distribution of communities of living organisms
• Croizat lived to see Plate Tectonics accepted as
  a Theory in the 1960s
• He was still writing scientific papers when he
  died at age 88!

118
Léon Croizat

• Based on the metaphor that "life and earth evolve
  together" -which means that geographic barriers
  and biotas co-evolve ? Croizat developed a new
  biogeographic methodology, which he named
  Panbiogeography.
• This method was basically to plot distributions
  of organisms on maps and connect the disjunct
  distribution areas or collection localities
  together with lines called tracks.
• Croizat found that individual tracks for
  unrelated groups of organisms were repetitive,
  and considered the resulting summary lines as
  generalized tracks which indicated the
  preexistence of ancestral biotas, subsequently
  fragmented by tectonic and/or climatic changes.

119
Croizats Panbiogeographic Tracks
Similar taxa or communities of taxa are linked
along the panbiogeographic tracks.
120
Dispersal Versus Vicariance

• Darwin, Wallace, Simpson, and most other
  biogeographers, before the 1960s, looked for
  dispersal events to explain distributions.

Croizat and his disciples offer an alternative
Vicariance.
121
Dinosaur Distribution Vicariance

• During the middle of the Mesozoic era, the
  dinosaur Allosaurus occupied the large, single
  continent of Pangaea.
• Subsequently, as this continent broke apart,
  populations of Allosaurus became isolated from
  each other and speciated into other derivative
  carnivorous species (Gigantotosaurus,
  Carcharodontosaurus, Acrocanthosaurus).
• The forming continents drifted into their present
  positions today.
• The location of these fossil remains, now carried
  into distant locations, are indicated by red
  dots.

122
Cladistic Biogeography

• Upper figure shows a cladogram based on geologic
  evidence for breakup of Gondwanan continents
• Lower figure uses the distributions of some
  shared taxa (hylid frogs, ratite birds, and
  xylontine fishes) to estimate breakup of Pangean
  continents

123
Other Biogeographical Concepts

• dispersal barrier or ecological barrier An area
  of unfavourable habitat that separates two areas
  of favourable habitat
• oceans or rivers for terrestrial organisms
• desert or grassland for of woodland organisms.
• waterfalls for river/stream organisms
• etc.

124
Other Biogeographical Concepts

• sweepstakes dispersal An unlikely chance event
  which carries a few individuals to a new and
  distant piece of favorable habitat

125
Other Biogeographical Concepts

• founder effect the loss of genetic variation
  when a new colony is established by a very small
  number of individuals from a larger population.
• It was first fully outlined by Ernst Mayr in
  1952.
• As a result of the loss of genetic variation, the
  new population may be distinctively different,
  both genetically and phenotypically, from the
  parent population from which it is derived.
• In extreme cases, the founder effect may lead to
  the speciation and subsequent evolution of new
  species.

126
Other Biogeographical Concepts
Zhejiang province, Eastern China

• bottleneck effect an evolutionary event in which
  a significant percentage of a population or
  species is killed or otherwise prevented from
  reproducing, and the population is reduced by 50
  or more, often by several orders of magnitude.
• Population bottlenecks increase genetic drift, as
  the rate of drift is inversely proportional to
  the population size.
• They also increase inbreeding due to the reduced
  pool of possible mates.

127
Summary Main Sources of Evidence for Evolution

• Comparative Studies
• Demonstration of Homologies
• Demonstration of Shared Derived Characters
• The Geological and Paleontological Record
• Biogeographical Distribution Patterns

128
Is There Necessarily a ConflictBetween Science
and Religion?

• Methodological Naturalism The only hypotheses
  researchers propose to account for natural
  phenomena, and the only explanations they accept,
  are hypotheses and explanations that involve
  strictly natural causes.
• Ontological Naturalism The natural world, the
  physical material universe, is all there is.
• There are scientists in both camps.

129
Further Reading
130
Conclusion

• The theme of this chapter is that the scientific
  evidence for the occurrence of evolution is now
  overwhelming and no educated person should doubt
  the fact of evolution.
• There can be no contradiction whatsoever between
  believing in evolution and believing in a God or
  creative force behind the universe.
• However, there is plenty of evidence to
  contradict the concept of an Intelligent
  Designer.
• But the conflict goes on . . .

131
End Chapter 6
132

• "Even more peculiar is the course of the
  recurrent laryngeal nerve, which corrects the
  brain to the larynx and allows us to speak. In
  mammals, this nerve avoids the direct route
  between brain and throat and instead descends
  into the chest, loops around the aorta near the
  heart, then returns to the larynx. That makes it
  seven times longer than it needs to be! For an
  animal like the giraffe, it traverses the entire
  neck twice, so it is fifteen feet long (fourteen
  feet of which are unnecessary). Not only is this
  design wasteful, but it also makes an animal more
  susceptible to injury. Of course, the bizzare
  pathway of this makes perfect sense in
  evolutionary terms. In fish and early mammal
  embryos, the precursor of the recurrent laryngeal
  nerve attached to the sixth gill arch, deep in
  the neck and body region. Fish still retain this
  pattern, but during late human embryology, the
  gill arches are modified into the tissues of our
  throat region and pharynx. Parts of the old
  fish-like circulatory system were rearranged, so
  the aorta (also part of the sixth gill arch)
  moved back into the chest, taking the recurrent
  laryngeal nerve (looped around it) backward as
  well." (Prothero, Donal R. "Evolution What the
  Fossils Say and Why It Matters", 2007, pp.
  37-38.)