25.1 Conditions on Early Earth made the foundation of life possible.

25.1 Conditions on Early Earth made the foundation of life possible

Steps for the start of Life

• 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.

Figure 25.3

(a) Self-assembly

Time (minutes)

Precursor molecules plusmontmorillonite clay

Precursor molecules only

Rel

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(b) Reproduction (c) Absorption of RNA

Vesicle boundary

1 m

0

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4020 60

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

• Fossils settle in layers of sedimentary rock that gets buried over time

• Dated by radiometric

dating

Fossil record

Origin of New Groups of Organisms

• 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

© 2011 Pearson Education, Inc.

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


Stromatolites

Figure 25.8

“Oxygen revolution”

Time (billions of years ago)

4 3 2 1 0

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100

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Figure 25.UN04

Single-celledeukaryotes

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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


Figure 25.9-3

Plasma membrane

DNA

Cytoplasm

Ancestralprokaryote

Nuclear envelope

Nucleus Endoplasmic reticulum

Aerobic heterotrophicprokaryote

Mitochondrion

Ancestralheterotrophic eukaryote

Photosyntheticprokaryote

Mitochondrion

Plastid

Ancestral photosyntheticeukaryote

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


Figure 25.UN05

Multicellulareukaryotes

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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


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


Why eukaryotic size limit until 575 m.y.a.?

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


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


Arthropods and tetrapods are the most widespread and diverse land animals

Tetrapods evolved from lobe-finned fishes around 365 million years ago


Section 25.4 The rise and fall of groups of

organisms reflect differences in speciation and extinction rates

Carly Timpson18 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

• Pangea separated (250 mya)

○ Deepened ocean basins lowered sea level

■ Shallow water habitats ruined

■ Cold, dry climate drove species to extinction

• Continent shifts locations to different climate

• Separation causes allopatric speciation

• Explains geographic distribution of organisms

Mass Extinction

• 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

• 50% or more of the earth’s marine species became extinct in all 5

• Permian (251 mya)o 96% of marine life wiped outo Volcanic eruptions

• Cretaceous (65.5 mya)o Over half of all marine species, terrestrial species including all

dinosaurso Clay enriched in iridium asteroid

• Possible 6th mass extinction?o Human actionso Within next few centuries/ millennia

Consequences of Mass Extinctions

● Reduction of ecological community complexity

● Evolutionary lineages cannot be repeated

● Type of organisms changes

Paleozoic Mesozoic Cenozoic

E O S D C P Tr J C P N

542 488 444 416 359 299 251 200 145 65.5 Q 0

50

0

Adaptive Radiation

• 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)

Sections 25.5 and

25.6

Erin FoeriMr. Reis

AP Biology18 December 2013

Effects of Developmental Genes:Heterochrony: changes in rate and

timing of developmental eventsPaedomorphosis: reproductive

traits develop faster than non-reproductive; juvenile traits of ancestor found in adult stage of descendent

Changes in Hox genes: huge impact on morphology

Concept 25.5- Major changes in body form can result from changes in the sequences and regulation of developmental genes

Example of paedomorphosis

The Evolution of Development Changes in nucleotide sequences of developmental gene

Developmental gene mutations affecting regulation

…Concept 25.5 (continued)

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

Concept 25.6- Evolution is not goal oriented

Evolutionary Novelties

Evolutionary TrendsCaused by gradual factors over time (natural

selection)Must be examined in a broad senseEx. Evolution of one horse species indicates

trend towards large sizeDemonstrates that evolution is not “goal-

oriented” towards a particular trait

…Concept 25.6 (continued)

Chapter 26Phylogeny and the Tree of LifeSection 1

Concept 26.1: Phylogenies show evolutionary relationships

• 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

Binomial Nomenclature• Carolus Linnaeus: published a system of

taxonomy based on resemblances• His System Today:

• Two-part names for species• Hierarchical classification

Parts of Carolus Linnaeus system• 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

Linking Classification and Phylogeny• Systematists depict evolutionary relationships in

branching phylogenetic trees

Order Family

Pantherapardus(leopard)

Genus Species

Canislatrans(coyote)

Taxideataxus(Americanbadger)

Lutra lutra(Europeanotter)

Canislupus(gray wolf)

Felid

ae

Carn

ivora

Pan

thera

Taxid

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Mu

stelidae

Lu

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Can

idae

Can

is

• 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

What We Can and Cannot Learn from Phylogenetic Trees

• 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

Applying Phylogenies• 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

Chapter 26Section 2

Jake Clarke

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

Phylogenies are inferred from morphological and molecular data

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.

Morphological and Molecular Homologies

Ex.) Bats and birds vs. Bats and Cats Analogous-mutual flight ability

Homology- comparing bone structure

Sorting Homology from Analogy

Cat ForearmBat forearm

Comparing DNA molecules can help identify homologies, although throughout many generations insertions and deletions have caused the DNA to vary.

Evaluating Molecular Homologies

Morphological Homology

Morphological AnalogyAustralian “mole”

Eutherian North American Mole

26.2 Phylogenies are inferred from morphological and

molecular data

• 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.

Homologies are similarities due to shared ancestry

Analogies are similarities due to convergent evolution

How to determine whether a similarity is a result of Homology

or Analogy

Distinguishing between homology and analogy is critical in reconstruction phylogenies.

Analogous structures that arose independently are called Homoplasies

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.

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

Evaluating Molecular Homologies

Molecular Systematics uses molecular data (DNA) to determine evolutionary relationships.

Aligning segments of DNA using Molecular Systematics

26.3 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

Ancestral gene

Ancestral species

Speciation with divergence of gene

Orthologous genes

Species A Species B

Ancestral gene

Ancestral species

Species C

Species C after many generations

Gene duplication and divergence

Paralogous genes

Formation of paralogous genes

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 ago2. 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

Divergence time (millions of years)

30 90

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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

25.1 Conditions on Early Earth made the foundation of life possible.

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