Transcript 25.1 Conditions on Early Earth made the foundation of life

25.1 Conditions on Early Earth made
the foundation of life possible
Steps for the start of Life
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Synthesis of molecules abiotically.
Polymerization of said molecules
Self replication of molecules
Creation of protocells.
Abiotic Molecules
• Simple molecules can form on their own
without life.
• Amino acids, etc.
• Oparin and Haldane experiments.
Polymerization
• Monomers can polymerize when dropped on
hot sand or clay.
• No enzymes required.
Relative turbidity,
an index of vesicle number
Figure 25.3
0.4
Precursor molecules plus
montmorillonite clay
0.2
Precursor
molecules only
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40
Time (minutes)
60
(a) Self-assembly
Vesicle
boundary
20 m
(b) Reproduction
(c) Absorption of RNA
1 m
Protocells
• Primitive lipid layers containing RNA, not DNA.
• Internal chemistry different from outside.
• Lipids can form membranes spontaneously in
water.
• Clay aids in membrane formation.
Fossil record
documents the history of
life
25.2
Fossil Record
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Fossils settle in layers of sedimentary rock
that gets buried over time
Dated by radiometric
dating
Fossil record
Origin of New Groups of Organisms
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Stemming from fossil record, organisms can
arise from gradual modifications of
preexisting organisms
Concept 25.3: Key events in life’s history
include the origins of single-celled and
multicelled organisms and the colonization
of land
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Table 25.1
The First Single-Celled Organisms
The oldest known fossils are stromatolites, rocks
formed by the accumulation of sedimentary layers
on bacterial mats
Stromatolites date back 3.5 billion years ago
Prokaryotes were Earth’s sole inhabitants from 3.5
to about 2.1 billion years ago
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Stromatolite
s
Atmospheric O2
(percent of present-day levels; log scale)
Figure 25.8
1,000
100
10
1
0.1
“Oxygen
revolution”
0.01
0.001
0.0001
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3
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Time (billions of years ago)
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0
Figure 25.UN04
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Singlecelled
eukaryotes
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The First Eukaryotes
The oldest fossils of eukaryotic cells date back 2.1
billion years
Eukaryotic cells have a nuclear envelope,
mitochondria, endoplasmic reticulum, and a
cytoskeleton
The endosymbiont theory proposes that
mitochondria and plastids (chloroplasts and
related organelles) were formerly small
prokaryotes living within larger host cells
An endosymbiont is a cell that lives within a host
cell
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Figure 25.9-3
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Photosynthetic
prokaryote
Mitochondrion
Nuclear envelope
Aerobic heterotrophic
prokaryote
Mitochondrion
Plastid
Ancestral
heterotrophic eukaryote
Ancestral photosynthetic
eukaryote
Key evidence supporting an endosymbiotic origin of
mitochondria and plastids:
Inner membranes are similar to plasma membranes
of prokaryotes
Division is similar in these organelles and some
prokaryotes
These organelles transcribe and translate their own
DNA
Their ribosomes are more similar to prokaryotic than
eukaryotic ribosomes
© 2011 Pearson Education, Inc.
Figure 25.UN05
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4
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Multicellular
eukaryotes
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The Earliest Multicellular Eukaryotes
Comparisons of DNA sequences date the common
ancestor of multicellular eukaryotes to 1.5 billion
years ago
The oldest known fossils of multicellular eukaryotes
are of small algae that lived about 1.2 billion years
ago
© 2011 Pearson Education, Inc.
Why eukaryotic size limit until 575
m.y.a.?
The “snowball Earth” hypothesis suggests that
periods of extreme glaciation confined life to the
equatorial region or deep-sea vents from 750 to
580 million years ago
The Ediacaran biota were an assemblage of larger
and more diverse soft-bodied organisms that lived
from 575 to 535 million years ago
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Figure 25.UN06
Animals
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The Cambrian Explosion
The Cambrian explosion refers to the sudden
appearance of fossils resembling modern animal
phyla in the Cambrian period (535 to 525 million
years ago)
A few animal phyla appear even earlier: sponges,
cnidarians, and molluscs
The Cambrian explosion provides the first evidence
of predator-prey interactions
Some DNA and fossil evidence suggest animal
phyla divergence prior to Cambrian Explosion
© 2011 Pearson Education, Inc.
Figure 25.UN07
Colonization of land
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The Colonization of Land
Fungi, plants, and animals began to colonize land
about 500 million years ago
Vascular tissue in plants transports materials
internally and appeared by about 420 million years
ago
Plants and fungi today form mutually beneficial
associations and likely colonized land together
© 2011 Pearson Education, Inc.
Arthropods and tetrapods are the most widespread
and diverse land animals
Tetrapods evolved from lobe-finned fishes around
365 million years ago
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Section 25.4
The rise and fall of groups of organisms
reflect differences in speciation and
extinction rates
Carly Timpson
18 December 2013
Plate Tectonics
● One supercontinent broke apart
● Plates on earth’s crust float atop the hot mantle
● Movements in the mantle shift these plates
○ Continental Drift
○ Magnetic signals provide information, such as previous location
○ Plates move slowly
○ Plate interaction is cause of earthquakes, volcanoes, islands, and mountains
Continental Drift
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Pangea separated (250 mya)
○ Deepened ocean basins
lowered sea level
■ Shallow water habitats ruined
■ Cold, dry climate drove species to extinction
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Continent shifts locations to different climate
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Separation causes allopatric speciation
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Explains geographic distribution of organisms
Mass Extinction
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Most species that have lived are extinct
○ Changes in environment
○ Habitat destroyed
○ Biological changes
Mass extinction is when disrupted global environmental changes cause the
rate of extinction to increase
“Big Five” Mass Extinction Events
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50% or more of the earth’s marine species became extinct in all 5
Permian (251 mya)
o 96% of marine life wiped out
o Volcanic eruptions
Cretaceous (65.5 mya)
o Over half of all marine species, terrestrial species including all
dinosaurs
o Clay enriched in iridium asteroid
Possible 6th mass extinction?
o Human actions
o Within next few centuries/ millennia
Consequences of Mass Extinctions
● Reduction of ecological community complexity
● Evolutionary lineages cannot be repeated
● Type of organisms changes
50
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N
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Paleozoic
Cenozoic
444 416
Mesozoic
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D
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C
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Tr
65.5
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Q
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Adaptive Radiation
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Evolution of diversely adapted species from a common ancestor
Follow mass extinctions, evolution of novel characteristics, and
colonization of new regions
Worldwide
Mammals after dinosaur
extinction
Regional (Hawaii)
Erin Foeri
Mr. Reis
AP Biology
18 December 2013
Effects of Developmental
Genes:
Heterochrony: changes in rate
and timing of developmental
events
Paedomorphosis:
reproductive traits develop
faster than nonreproductive; juvenile traits
of ancestor found in adult
stage of descendent
Changes in Hox genes: huge
impact on morphology
Example of paedomorphosis
…Concept 25.5 (continued)
The Evolution of Development
 Changes in nucleotide sequences of
developmental gene
Developmental gene mutations affecting
regulation
Evolutionary Novelties
Evolution- new species arise from slight
modifications of ancestors
Ex. Eyes evolved from simple structures to more
complex
Exaptations- structures that evolve for a
function, but eventually take on a new function
*Natural selection does not predict future, it
only can improve use of structure
Evolutionary Trends
Caused by gradual factors over time (natural
selection)
Must be examined in a broad sense
Ex. Evolution of one horse species indicates
trend towards large size
Demonstrates that evolution is not “goaloriented” towards a particular trait
Phylogeny and the Tree of Life
Section 1
• Phylogeny: The evolutionary history of a species or group of
related species
• Systematics: classification organisms and determines their
evolutionary relationships
• Systematists: Scientists who use fossil and genetic data to look
for evolutionary relationships among animals
• Taxonomy: The ordered division and naming of organisms
• Carolus Linnaeus: published a system of taxonomy based on
resemblances
• His System Today:
• Two-part names for species
• Hierarchical classification
• The two-part scientific name of a species is called a binomial
• The first is the genus
• The second part, called the specific epithet, is unique for each
species within the genus
• The first letter of the genus is capitalized, and the entire species
name is italicized
• Both parts together name the species (not the specific epithet
alone)
domain
kingdom
phylum
class
order
family
genus
species
Eukarya
Animalia
Chordata
Mammalia
Carnivora
Felidae
Panthera
Panthera pardus
• Systematists depict evolutionary relationships in branching
phylogenetic trees
Order
Family Genus
Species
Panthera
Felidae
Panthera
pardus
(leopard)
Taxidea
Lutra
Mustelidae
Carnivora
Taxidea
taxus
(American
badger)
Lutra lutra
(European
otter)
Canis
Canidae
Canis
latrans
(coyote)
Canis
lupus
(gray wolf)
• Linnaean classification and phylogeny can differ from each
other
• Systematists have proposed the PhyloCode, which recognizes
only groups that include a common ancestor and all its
descendants
• A phylogenetic tree represents a hypothesis about evolutionary
relationships
• Each branch point represents the divergence of two species
• Sister taxa are groups that share an immediate common
ancestor
• A rooted tree includes a branch to represent the last common
ancestor of all taxa in the tree
• A basal taxon diverges early in the history of a group and
originates near the common ancestor of the group
• A polytomy is a branch from which more than two groups
emerge
• Phylogenetic trees show patterns of descent, not phenotypic
similarity
• Phylogenetic trees do not indicate when species evolved or how
much change occurred in a lineage
• It should not be assumed that a taxon evolved from the taxon
next to it
• Phylogeny provides important information about similar
characteristics in closely related species
• A phylogeny was used to identify the species of whale from
which “whale meat” originated
Jake Clarke
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Analogy-similarity due to convergent
evolution
Homology-similarity due to shared ancestry
Homoplasies- analogous structures or
sequences that evolved independently
Molecular systematics -DNA and other
molecular data used to determine
evolutionary relationships
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Morphological Homologies- Similarity in an
animals structure due to homologous
ancestry. Although morphological differences
may be vast but molecular differences can be
similar (or vice versa)
Molecular homologies -an organism with
similar morphological features are more likely
to be closer than another animal with
dissimilar structures or sequences.

Ex.) Bats and birds vs. Bats and Cats
Analogous-mutual flight ability
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Homology- comparing bone structure
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Cat Forearm
Bat forearm
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Comparing DNA molecules can help identify
homologies, although throughout many
generations insertions and deletions have
caused the DNA to vary.
Australian “mole”
Eutherian North American Mole
• Organisms that share very similar morphologies and (or)
molecular data are very likely to be more closely related than
organisms that differ in phenotype or sequence.
How to determine whether a similarity
is a result of Homology or Analogy
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Distinguishing between homology and analogy
is critical in reconstruction phylogenies.
 Homologies are similarities due to shared ancestry
 Analogies are similarities due to convergent evolution
Analogous structures that arose
independently are called Homoplasies
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The more elements similar in two complex structures,
the more likely they evolved from a common ancestor
Since human and
chimpanzee skulls have a
close resemblance, it is
improbable that such
complex structures have
separate origins.
Evaluating Molecular
Homologies
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 Scientists have created computer programs to
estimate the best way to align comparable DNA
segments of different lengths despite insertions and
deletions that accumulate over long periods of time.
 Segments that resemble each other at many points
along their lengths are usually homologous
Aligning segments of DNA
using Molecular Systematics
Molecular
Systematics
uses molecular data
(DNA) to determine
evolutionary
relationships.
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Shared Characteristics are used to construct
phylogenetic trees
Cladistics
● Cladistics--an approach to systematics
○ used to place species into ‘clades’
■ each include an ancestral species and all of its descendants
■ clades reside in other, larger clades
● Monophyletic
○ a clade consisting of ancestral species and all of its
descendants
● Paraphyletic
○ a clade consisting of ancestral species and some, but not
all, of its descendants
Shared Ancestral/ Derived Characters
● Shared ancestral character
○ a character that originates in an ancestor and is present in
the descendant
● Shared derived character
○ shared by all organisms in a clade but not with their
ancestors
Inferring Phylogenies Using Derived
Characters
● For a basis of comparison an outgroup is needed
● The studied organism is the ingroup
Phylogenetic Trees w/Proportional Branch Lengths
● Some trees branch lengths are proportional to the
amount of evolutionary change or to the times at which
particular events occurred
● In some trees, the length of a branch can reflect the
number of genetic changes that have taken place in a
particular DNA sequence in that lineage
Maximum Parsimony and Maximum
Likelihood
● These are utilized to choose the best tree in a large data
set
● Parsimony
○ ‘Cut-away’ method removing unnecessary
complications
● Likelihood
○ a tree can be selected that reflects the most likely
sequence of evolutionary events
Phylogenetic Trees as Hypotheses
● Phylogenetic bracketing allows us to predict features of
an ancestor from features of its descendants
● supported by the fossil record
Concept 26.4: An organism’s evolutionary
history is documented in its genome
• Gene Duplications and Gene Families
– Orthologous genes: homologous genes found in
different species (result of speciation)
• Divergence can be traced back to speciation event
– Paralogous genes: homologous genes within a
species that result from gene duplication
• Often evolve new functions because duplication
increases number of genes in genome, providing more
opportunity for mutation and evolutionary change
Two types of homologous genes; Colored bands mark regions of
the genes where differences in base sequences have
accumulated
Formation of orthologous genes
Formation of paralogous genes
Ancestral species
Ancestral species
Ancestral gene
Ancestral gene
Species C
Speciation with
divergence of gene
Gene duplication
and divergence
Species B
Species A
Orthologous genes
Paralogous genes
Species C after many
generations
Genome Evolution
• 1. Lineages that diverged long ago can share
orthologous genes
– Ex. 99% of genes of humans and mice are
orthologous, diverged about 65 million yrs ago
2. Number of genes a species has does not increase
through duplication at a rate consistent with
phenotypic complexity
– Ex. Humans have 4x the genes of yeast, but are
much more complex
– Genes in complex organisms=multi-functional
Concept 26.5-Molecular clocks help
track evolutionary time
• Molecular Clock-region of DNA in which
amount of genetic change is consistent
enough to be used to estimate the date of
past evolutionary events
– Orthologous genes: nucleotide substitutions
proportional to the time since they last shared a
common ancestor
– Paralogous genes: nucleotide substitutions
proportional to the time since the genes became
duplicated
A molecular clock for mammals
Number of mutations
90
60
30
30
Divergence time (millions of years)
90
Neutral Theory
• Evolutionary change in genes and proteins has
no effect on fitness, not influenced by nat. sel.
• Mutations that are harmful are removed, but
most=neutral, so rate of molecular change
should be regular
Problems with Molecular Clock and
Origin of HIV
• Some DNA regions change in less predictable
way
• Natural selection can favor some DNA changes
over others-produces irregularities
• Molecular clock analysis shows strain of HIV
jumped from primates to humans multiple
times, beginning in 1930s