Evolution

Evolution = “Descent with Modification”

1. Organisms evolved due to being spread over different habitats and therefore adapting and modifying themselves to fit the habitat.

2. Natural Selection • A population of organisms

can change over generations if certain inheritable traits leave more offspring than others and those others get the chance to reproduce and continue the lineage.

• Evolutionary Adaptation

Descent with modification

Evolutionary Adaptation

Evidence of Evolution:Fossil Record

Fossils chronologically ordered in rock layers

Evidence of Evolution:Biogeography

Geographic distribution of species: Australian marsupials

Evidence of Evolution:Comparative Anatomy and Embryology

HOMOLOGY

Evidence of Evolution:Molecular Biology

Notice that a Chimp is more genetically related to a human than to an Old World Monkey!

Adaptive Evolution

The finches of The Galapagos Islands: The original finch developed into 14 different species. What was the cause for the offshoots?

Natural Selection = Editing

Darwinism Meets Genetics• A population is the smallest unit of evolution.

– Natural selection acts on individuals.– However the evolutionary impact of natural selection is only

apparent in tracking how a population changes over time.• Population Genetics emphasizes the extensive genetic variation

within populations and tracks the genetic make-up of populations over time.– Not all variation in a population is inheritable.– Only the genetic component of variation is relevant to natural selection.– Many variable traits in a population result from the combined effect of

several genes.

Polymorphism

Analyzing Gene Pools

• A Gene pool consists of all alleles (different forms a gene may have for a trait) in all the individuals making up a population.– A reservoir for the next generation’s genes.

• Recall: Homozygous (RR) and Heterozygous (Rr) Dominant and Recessive (rr)– Hardy Weinberg Formula (1908)

• Helps to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles and vice versa.

• p2 + 2pq + q2 = 1– p = RR– pq = Rr– q = rr

Practice Using The Hardy-Weinberg Formula

p2 + 2pq + q2 = 1

p = 0.6q = 0.4

What are the genotypic frequencies of their offspring?

0.36 + 2(0.24) + 0.16 = 136% RR48% Rr16% rr

Microevolution1. Genetic Drift Def: A change in the gene pool of a small population due to chance.

The best measure of Darwinian fitness is the number of fertileoffspring an individual leaves.

Genetic equilibrium- allele frequencies

remain constant.

To maintain equilibrium…

1.Random mating

2.Population must be very large

3.No immigration or emmigration

4.No mutations

5.No natural selection

Types of Genetic Drift

a. The Bottleneck Effect• An event that usually reduces the overall genetic variability in

a population.

b. The Founder Effect• Genetic Drift in a new colony• i.e. The Galapagos Islands

Microevolution Cont.2. Gene Flow

Def: The genetic exchange with another population.

3. Mutations– A change in an organism’s DNA sequence.– Ultimate source of genetic variability.

4. Natural Selection– Directional Selection (selecting in favor of an extreme phenotype)– Disruptive (Diversifying) Selection (leads to a balance between two or

more contrasting phenotypic forms)– Stabilizing Selection (maintains variation in a narrow range)

• Resistant Genes• Immediate Benefits• Long term Disaster• Evolution direct

connection to daily lives

Macroevolution

• Def: Major biological changes evident in fossil record.

• CONTRAST: MICROEVOLUTION• Speciation

– Nonbranching evolution (transform a population enough for it to be designated a new species.)

– Branching evolution (splits a lineage into two or more species)

The Origins of Species• Ernst Mayr

– Studied the diversity of birds in New Guinea (1927)– Biological species concept

• Species = “groups of interbreeding natural populations that are reproductively isolated from other such groups.”

• Reproductive isolation blocks exchange of genes between species and keeps their gene pools separate.

• Reproductive barriers between species• Zygote: fertilized egg• Pre-zygotic (factors that impede mating

between species or hinder fertilization of eggs if mating is attempted)

• Post-zygotic (mechanisms that operate should interspecies mating actually occur and form hybrid zygotes)

Courtship

Sterile

Isolating Mechanisms

Mechanisms of Speciation

• Allopatric Speciation– A population forms a

new species while geographically isolated from its parent population.

• Sympatric Speciation– A small population

becomes a new species in the midst of a parent population

• Speciation occurs only with the evolution of reproductive barriers between the isolated population and its parent population.

• If speciation occurs during geographic separation, the new species will not breed with its ancestral population, even if the two populations should come back into contact.

Sympatric Speciation

• Does not widely occur among animals but may account for over 25% of all plant species.

Notice how the hybrid bread wheat has a set of chromosomes from each of its ancestors: T. monococcum (AA), Triticum (BB), T. turgidum (AA BB), T. tauschii (DD)

What can you notice about T. aestivum that might make it a good hybrid and the most important wheat species today?

Relative Dating:Fossil Record

Fossils chronologically ordered in rock layers

Radioactive Dating

Continental Drift

Theory: 65 million years ago a catastrophic event occurred killing off the dinosaurs and about ½ of the species inhabiting the Earth in a 10 million year time span.

Meteor of this size would have lowered the temperature of Earth due to the blocking of the sun by atmospheric dust.

The Origin of Life

• Stage 1: Abiotic Synthesis of Organic Monomers– Amino Acids

• Chains of nucleotides– Chains of DNA bases– Chains of RNA bases

• Building blocks of protein

– Sugars– Lipids– ATP

The Origin of Life

• Stage 2: Abiotic Synthesis of Polymers– Monomers, such as amino acids,

spontaneously fused together to form proteins.

The Origin of Life

• Stage 3: Origin of Self-Replicating Molecules

inheritance

Ribozyme: catalytic RNA used to fuel RNA replication

The Origin of Life

• Stage 4: Formation of Pre-cells– Molecular packages

with some properties of life.

– The gap between pre-cells and true cells is enormous!• Natural Selection

The origin of

eukaryotic cells

Endosymbiotic Theory

– Membrane bound nuclear material

– Organelles– More complex than prokaryotic

cells– Ancestors to fungi, plants and

animals

Concept Map

Evolution of Life

Section 17-2

Early Earth was hot; atmosphere contained poisonous gases.

Earth cooled and oceans condensed.

Simple organic molecules may have formed in the oceans..

Small sequences of RNA may have formed and replicated.

First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.

Later prokaryotes were photosynthetic and produced oxygen.

An oxygenated atmosphere capped by the ozone layer protected Earth.

First eukaryotes may have been communities of prokaryotes.

Multicellular eukaryotes evolved.

Sexual reproduction increased genetic variability, hastening evolution.

Convergent Evolution

• Process by which unrelated animals come to look like each other.

• Dolphin• Penguin• Shark

Tempo of Evolution

Slow adaptations

Spurts of relatively rapid change

Section 17-4

Flowchart

that are

can undergo can undergo can undergo can undergo can undergo

in underunderform inin

Species

Unrelated Related

Inter-relationshiops

Similar environments

Intense environmental

pressure

Small populations

Different environments

Coevolution Convergent evolution

ExtinctionPunctuated equilibrium

Adaptive radiation

Classifying the Diversity of Life

• Systematics– Reconstructing evolutionary history– Radioactive dating = tool– The study of biological diversity: past and present

• Taxonomy– Identification, naming and classification of species– Pioneer: Carolus Linnaeus (1707-1778)

• Binomial Nomenclature• Homo sapien

Hierarchical Classification

Which step is more specific?

Class or Genus?

How is Domain Eukarya different from Bacteria and

Archaea?

Phylogeny

• Evolutionary history of a species.

• Tree is based on homologous structures, NOT analogous.

• Two species will have more common nucleotide sequences based on how recently they branched from their common ancestor.

The Cladistic Revolution

The Computer Age

6 Kingdoms vs. 3 Domains

?

EubacteriaArchaea-bacteria