Evidence for evolutionary change

1
Evidence for evolutionary change

• Fossil record
• Biogeography
• Convergent evolution
• Homologies
• Anatomical
• Developmental
• Molecular

2
The Fossil Record

• How fossils form
• How fossils are dated
• Contributions and limitations of the fossil record

3
How Fossils Form

• The remains or traces of organisms left in
  sedimentary rock
• Sediment (pebbles, sand, silt, or clay)
  accumulate over time and exhibit distinct layers
• Oldest (bottom), youngest (top)

4
The Geological Formation of Fossils
Trilobite 500 mya
5
Types of Fossils

• Hard body parts
• Bones and Teeth
• Shells
• Over 300,000 fossil species have been described
  and named!

6
Dinosaur footprints

• Impression or imprint
• Mineralization (petrified wood)
• Casts and Molds

Casts of Echinoderms
Leaf Impression
Petrified Wood
7
Ice and Amber

• Ice is an excellent preservative
• Mammoth preserved in ice for over 25,000 years
• Allows for DNA analysis
• Amber 2 mya insect in amber

8
Fossil Dating

• Relative Dating
• relative position in sedimentary rocks
• index fossils
• Absolute dating
• radioisotopes

9

• Rock formation occurs in a time ordered sequence
• Most fossils are dated by their relative position
  in sedimentary layers
• Index Fossils occur in specific layers of rock
  over a large geographical range

10
Absolute Dating with Isotopes

• All atoms are isotopes
• Most isotopes are stable
• Some are unstable change to form other elements
• Energetic emissions given off during isotope
  breakdown are called radioactivity

Uranium-235 704 my Potassium-40 1.3 by decays
to Argon-40 Carbon-14 5740 years dating
organic remains up to 50,000 years
11
Absolute Dating
12
Fossils

• Even with an incomplete fossil record,
  evolutionary changes can be demonstrated
• Fishapod
• Oysters
• Horse family

13
Fishapod (Tiktaalik roseae)

• Illuminates steps leading to evolution of
  tetrapods
• Transitional form provides link between earlier
  and later forms
• Had broad skull, flexible neck, eyes on top,
  primitive wrist and 5 fingers
• Peek above water and look for prey

14
(No Transcript)
15
Oysters

• 200 mya some oysters underwent shell changes
• Smaller, curved shells were superseded by larger,
  flatter shells
• Flatter shells are more stable in disruptive
  water currents and so were better adapted when
  water currents became stronger

16
(No Transcript)
17
Horse family

• Earliest fossils were small with short legs and
  broad feet
• Adaptive changes
• Dog sized to more than half a ton
• 4 front toes/ 3 hind toes to single toe in a hoof
• Small teeth to much larger ridged teeth
• Attributed to adaptations to changing global
  climate

18
(No Transcript)
19
Biogeography

• Study of the geographical distribution of extinct
  and modern species
• The pattern of distribution
• pattern in time
• pattern in space
• Isolated continents and island groups have
  evolved their own distinct plant and animal
  communities
• Endemic naturally found only in a particular
  location
• Island fox (Urocyon littoralis) evolved from
  mainland gray fox (Urocyon cinereoargenteus)

20
(No Transcript)
21

• Evolution of major animal groups correlated with
  known changes in the distribution of land masses
  on the Earth
• Plate Tectonics or Continental drift helped make
  sense of current distributions

22
Continental Drift
Pangaea brought together terrestrial species that
had evolved separately from one another. This
created intense competition and some extinction
23
Continental Drift
Geographic isolation as continents drifted apart
and environmental conditions became different on
each land mass
24
(No Transcript)
25
Why are Australian animals unique?

• First mammals arose 225 mya when Australia was
  still connected
• Placental mammals arose 80 mya after Australia
  separated
• Australia has no large, terrestrial placental
  mammals

26
Convergent Evolution

• 2 different species from different lineages show
  similar characteristics because they occupy
  similar environments
• Examples of analogous (convergent) traits
• Giant anteater and echidna both have long snouts
  and tongues to feed on ants
• Aerial rootlets for clinging in English ivy and
  wintercreeper
• Antifreeze proteins in different very cold water
  fish

27

• Giant anteater
• South America
• Placental mammal
• Echidna
• Australia
• Monotreme mammal
• both have long snouts and tongues to feed on ant

28

• Aerial rootlets for clinging in English ivy and
  wintercreeper
• English Ivy (Hedera sp.)
• Wintercreeper (Euonymus sp.)

29

• Antifreeze proteins in different very cold water
  fish
• Sea Raven anti freeze protein evolved a gene
  rich in the a.a. cysteine.
• Longhorn Sculpin anti freeze protein evolved
  from the modification (mutation) of an entirely
  different gene

30
Homologies

• Comparing similarities and differences between
  organisms to infer their evolutionary
  relationships
• Anatomical
• Developmental
• Molecular (DNA and Protein sequences)
• Are you comparing the right thing?
• Requires knowing the difference between
  homologous and analogous structures
• Which structures are older/newer?
• Ancestral or primitive states
• Advanced or derived states

31
Homologies

• Homology a fundamental similarity that occurs
  due to descent from a common ancestor
• Homologous structures Structures that are
  similar to each other because they are derived
  from the same common ancestor.

32
A Cat is a Cat
Homology is based on the premise that organisms
with a suite of similar features tend to be
related by descent
Felidae
33
Organisms with a suite of similar features tend
to be related by descent
34
Analogous Structures The Evolution of Wings
.
35
Analogous Structures are a result of Convergent
Evolution

• Adaptations allow an organism to survive in a new
  environment
• Just because organisms look similar, it doesnt
  mean they are related or share the same
  evolutionary heritage
• Adaptations are not necessarily evidence that
  organisms are evolutionarily related

36
Homologous Structures

• Same set of bones in the limbs of modern
  vertebrates has undergone evolutionary change to
  be used for many different purposes
• Homologous structures are derived from a common
  ancestor

Descent with Modification
37
Modifications include the loss of structures

• Vestigial organs are remnants of past structures
  that are no longer of use
• Loss of legs (snakes), loss of wings (ratite
  birds)
• Human vestigial organs
• wisdom teeth
• appendix
• tail bone

38

• Analogous structures are fundamentally different
  structures adapted to the same ecological niche
• evolution of wings (ability to fly)
• evolution of fins (ability to swim)
• Homologous structures represent the same
  structure adapted to different ecological niches
• modification of the forearm for flight, swimming
  and walking
• All mammals have 7 neck bones (giraffe, human,
  whale)

39
Developmental homology

• Species that differ as adults often bear striking
  similarities during embryonic stages
• Presence of gill ridges in human embryos
  indicates that humans evolved from an aquatic
  animal with gill slits
• Human embryos have long bony tails

40
Molecular homology

• Similarities in cells at the molecular level
  indicate that living species evolved from a
  common ancestor or interrelated group of common
  ancestors
• All living species use DNA to store information
• Universal Genetic Code
• Certain biochemical pathways are found in all or
  nearly all species

41
The same type of gene is often found in diverse
organisms

• P53 plays a role in preventing cancer
• Certain genes are found in a diverse array of
  species
• Sequences of closely related species tend to be
  more similar to each other than to distantly
  related species

42
Amino Acid sequences for the p53 protein among
species
43
Molecular Processes Underlying Evolution

• Mutation
• Exon shuffling
• Gene duplication
• Horizontal gene transfer
• Changes in chromosome structure and number

44
Molecular Processes Underlying Evolution

• Homologous genes 2 genes derived from the same
  ancestral gene
• Reveals molecular details of evolutionary change
• 2 sequences may be similar due to the same
  ancestral gene but not identical due to the
  independent accumulation of different random
  mutations

45
New Genes in Eukaryotes Have Evolved Via Exon
Shuffling

• Exon shuffling occurs when an exon and the
  flanking introns are inserted into a gene
  producing a new gene that encodes a protein with
  an additional domain
• Proteins can alter traits and be acted upon by
  natural selection
• May occur by more than one mechanism
• Double crossover
• Transposable elements

46
(No Transcript)
47
Paralogs are homologous genes within a single
species

• Gene duplication can lead to a gene family
• 2 or more paralogs within the genome of a single
  organism
• Globin genes coding for oxygen binding proteins

48
Horizontal Gene Transfer

• Exchange of genetic material among different
  species
• Vertical gene transfer involves evolution from
  pre-existing species by accumulation of
  mutations, gene duplications and exon shuffling
• Common phenomenon
• Prokaryotes to eukaryotes, eukaryotes to
  prokaryotes, between prokaryotes and between
  eukaryotes
• Widespread among bacteria

49
(No Transcript)
50

• Evolution also occurs at the genomic level
  involving changes in chromosome structure and
  number
• Compare 3 largest chromosomes in humans and apes
• Similar due to close evolutionary relationship
• Humans have 1 large chromosome 2 while apes have
  it divided into 2 separate chromosomes
• Chromosome 3 very similar but orangutans have a
  large inversion
• May have established orangutans as a new species

51
(No Transcript)