Mechanisms of Mechanisms of EvolutionEvolution

I. Natural Selection & I. Natural Selection & Charles DarwinCharles Darwin

Charles Darwin (1819-1882) an Charles Darwin (1819-1882) an English scientist considered the English scientist considered the founder of the evolutionary theoryfounder of the evolutionary theory

Evolution is often referred to as Evolution is often referred to as DarwinismDarwinism

Darwin studied many forms of life Darwin studied many forms of life through the voyage of the through the voyage of the BeagleBeagle

Galapagos Islands was where Darwin Galapagos Islands was where Darwin studied a majority of the organismstudied a majority of the organism

Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species

The Galapagos Islands:The Galapagos Islands: Darwin notes:Darwin notes:Island species Island species variedvaried from the from the mainland species, and from island-to-mainland species, and from island-to-islandisland Each island had either Each island had either long or short long or short neckednecked tortoises tortoises depending on the depending on the island's vegetationisland's vegetation

The Galapagos Islands:The Galapagos Islands: Darwin noted:Darwin noted: Finches: Bill shapes are adaptations Finches: Bill shapes are adaptations

to different means of gathering foodto different means of gathering food. .

Galapagos finch species varied by nesting site, beak size, and eating habits

The Theory of Evolution:The Theory of Evolution: Darwinism Darwinism

We have discussed the 4 supporting We have discussed the 4 supporting evidences of evolution.evidences of evolution. Comparative anatomyComparative anatomy Molecular BiologyMolecular Biology BiogeographyBiogeography EmbryologyEmbryology

Today we are going to discuss the 4 mechanisms of HOW Evolution occurs…

Outine: 4 Mechanisms of Outine: 4 Mechanisms of EvolutionEvolution

1.1. Natural SelectionNatural Selection

2.2. MutationMutation

3.3. MigrationMigration

4.4. Genetic DriftGenetic Drift

#1 Natural Selection:#1 Natural Selection: Natural Selection – AKA “Survival of Natural Selection – AKA “Survival of

the Fittest”the Fittest”

A gradual, non-random process by A gradual, non-random process by which biological traits become either which biological traits become either more or less common in a population more or less common in a population

As you can see there is a variation in the phenotype of these beetles: Green or brown

Genetic Variation: Genetic differences within a population.

The genetic variation in this scenario are the genes that code for the color of the beetle.

3 Types of Natural Selection 3 Types of Natural Selection that Act on Variation:that Act on Variation:

1. 1. StabilizingStabilizing – natural selection that – natural selection that favors average individualsfavors average individuals

3 Types of Natural Selection 3 Types of Natural Selection that Act on Variation:that Act on Variation:

2. 2. Directional selection Directional selection – natural – natural selection that favors an extreme form of selection that favors an extreme form of a traita trait

3 Types of Natural Selection 3 Types of Natural Selection that Act on Variation:that Act on Variation:

3. 3. Disruptive selectionDisruptive selection – individuals w/ – individuals w/ either extreme form of a traiteither extreme form of a trait

#2 Mutation#2 Mutation

Mutation: change in a gene; alteration of Mutation: change in a gene; alteration of a nucleotide sequence. a nucleotide sequence.

EX: A mutation causes two green beetle parents to have a brown beetle

#3 Migration#3 Migration

Migration: Movement of some individuals Migration: Movement of some individuals to another population to another population

Gene Flow – transfer of alleles from one population to another population through immigration of individuals . This disrupts allele frequency.

#4 Genetic Drift#4 Genetic Drift

Genetic DriftGenetic Drift: some individuals may by : some individuals may by chancechance and and not because of “fitness” not because of “fitness” leave more descendants and therefore leave more descendants and therefore pass on their genes.pass on their genes.

The Evolution of Species:The Evolution of Species: SpeciesSpecies – organisms that look alike can – organisms that look alike can

interbreed to produce fertile offspringinterbreed to produce fertile offspring SpeciationSpeciation – evolution of a – evolution of a newnew species. species.

*NOTE: Organisms within the same species have reproductive success ( ability to pass genes onto the next generation in a way that they too can pass on those genes.)

Donkey

+

Horse

=

Mule He can not have offspring because his parents are two different species

So how do new So how do new species come species come about?about?

1. 1. Geographic IsolationGeographic Isolation – a physical – a physical barrier divides a populationbarrier divides a population

Physical Barriers Cause Physical Barriers Cause Speciation:Speciation:

2. 2. Reproductive Isolation Reproductive Isolation – the inability of – the inability of organisms to mate and breed fertile organisms to mate and breed fertile offspringoffspring

Genetic material becomes so Genetic material becomes so different fertilization can not occurdifferent fertilization can not occur

Behavior – mating seasons are Behavior – mating seasons are differentdifferent

These Bowerbirds have different mating seasons and rituals. These 2 factors contribute to Reproductive Isolation

Does evolution happen fast or slow?

Speciation Rates - the time it takes for evolution to occur.

2 Theories:

#1 Gradualism: – idea that species originate through a gradual change of adaptations

Both!

# 2. # 2. Punctuated Equilibrium Punctuated Equilibrium : things : things staying the same for a period of time then staying the same for a period of time then rapidly changing due to a catastrophic rapidly changing due to a catastrophic event.event.

There are TWO types There are TWO types of Evolutionof Evolution

#1 #1 Divergent Evolution Divergent Evolution – accumulation – accumulation of differences between groups which of differences between groups which can lead to the formation of new speciescan lead to the formation of new species

#2 #2 Convergent Evolution Convergent Evolution – organisms not – organisms not closely relate, independently evolve closely relate, independently evolve similar traits (to adapt to similar similar traits (to adapt to similar environments.)environments.)

Genetics Determines Genetics Determines Evolution:Evolution: Gene Pool Gene Pool – All the alleles in a – All the alleles in a

populations genes. In other words every populations genes. In other words every form of a traitform of a trait

Allelic Frequency Allelic Frequency – the % of any specific – the % of any specific allele w/in a gene poolallele w/in a gene pool

Genetic Equilibrium – allele frequency Genetic Equilibrium – allele frequency remains the same over generationsremains the same over generations Populations in genetic equilibrium Populations in genetic equilibrium

are not evolvingare not evolving Factors that affects genes can affect Factors that affects genes can affect

equilibriumequilibrium

1. Mutations [negative, positive]1. Mutations [negative, positive] Negative more than likely causes Negative more than likely causes

deathdeath Positive may be beneficialPositive may be beneficial

Trait Variations – Trait Variations – differences in Organismsdifferences in Organisms

Increases or decreases an organisms Increases or decreases an organisms chance of survivalchance of survival

Inherited and controlled by allelesInherited and controlled by alleles Allelic frequencies in a populations gene Allelic frequencies in a populations gene

pool will change due to natural selectionpool will change due to natural selection

C. Patterns of EvolutionC. Patterns of Evolution1. Adaptive Radiation – ancestral species 1. Adaptive Radiation – ancestral species

evolves into an array of species to fit a evolves into an array of species to fit a particular environment.particular environment.