evolution concepts and mechanisms

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Evolution: Concepts o ut o Co ceptsand Mechanism

AP Biology Rapid Learning Series

Rapid Learning Centerwww.RapidLearningCenter.com/© Rapid Learning Inc. All rights reserved.

AP Biology Rapid Learning SeriesWayne Huang, PhD

Andrew Graham, PhDElizabeth James, PhD

Casandra Rauser, PhD Jessica Habashi, PhD

Sara Olson, PhDJessica Barnes, PhD



Learning Objectives

Understand the concept of

By completing this tutorial, you will learn about:

Understand the concept of Evolution.

Apply the concept to your life and the environment around you.

Hone your skills of analysis by judging the soundness of

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by judging the soundness of Darwin’s theory of Evolution.

Evolution Concept Map

DNA ChemicalStructure

Genes

Chromosomes

MendelianLaws

IndependentAssortment

Law of Segregation

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Structure Function

Meiosis

Mitosis

Seg egat o



Descent with Modification

Define “Descent With Modification”Natural SelectionNatural SelectionInheritance

Descent with Modification

Evolution is the change in inherited traits of a population.

Changes in genes are a function of mutations and selection.

Selection acts on the “generations”. Bacteria with a life span of 20 – 45

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minutes will evolve more rapidly then an organism that requires years to produce new generations.



Natural Selection

To understand Darwin’s theory you need to

understand the meaning of : descent

DescentRefers to the idea that current day organisms arose from older ancestral species of : descent,

modification and natural selection.

over time.

M difi ti

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ModificationModification is a mechanism or process of interaction between the environment and an organisms heritable constitution adaptation

Natural SelectionThe process in which

favorable traits that are heritable become more common in subsequent

generations.

Definition of InheritanceHeritable and inheritance

describes a trait that can be passed down from one generation

to the next. This includes hair l h i ht tcolor, height etc.

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Modification = Natural SelectionThe main mechanism of modification is via “Natural Selection”.

Random variation of traits in a

population

Interaction of species with

Adaptationmore offspring

carrying

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environmentDifferential

reproductive success of

species carrying

particular traits

y gadvantageous

traits

Natural Selection Targets

Natural selection acts on the phenotype which is the observable characteristics of an organism.

Individuals with favorable phenotypes are more likely to survive and reproduce than those with less f bl h tan organism. favorable phenotypes.

Over time this will result in an “adaptation” which causes the organism to specialize for a certain niche. This can even lead to the emergence of

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If the phenotype is due to a genetic difference that genotype will be selected for and its frequency in the next generation increased.

even lead to the emergence of a new species.



Genetic Variation and Selection

Genetic variation can occur when different organisms of a population

have different versions of a gene (allele)(allele).

Some traits are the result of a single gene.

Beak variation is an example.

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Some traits are the result of a single gene. Most traits are a result of interactions of many genes. Pleiotropy happens when a single gene influences many different phenotypic traits. A new mutation in the gene will have effects on

all traits simultaneously. Genetic linkage occurs when particular alleles are inherited

together.

Origin of the Species

Evolution and speciationSpecies originSpecies originPhylogenetic tree



Speciation & Origin

Speciation is the evolutionary process giving rise to a new

species. There are four modes of natural selection that give rise to a

A species is a taxonomic group who's members can

interbreed and produce fertile offspring. natural selection that give rise to a

new species and involves geographic isolation: allopatric,

peripatric, parapatric and sympatric. New species may also be produced by genetic engineering and animal

husbandry.

fertile offspring.

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Kinds of Geographic SpeciationAllopatric speciation, a

population is split into two geographically isolated

ones. The isolated l ti th d

Parapatric speciation, the geographic zones of the two diverging populations are separate but do overlap.

populations then undergo genotypic divergence.

Peripatric speciation a new species is formed in small

Individual of each species may come in contact or mate but the fitness of the heterozygote is reduced so selected against.

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species is formed in small isolated peripheral

populations which are prevented from exchanging

genes with the main population.

Sympatric speciation species diverge while inhabiting the

same place e.g. insects which become dependent on

different host plants in the same area.



Phylogenetic Tree of LifeA phylogenetic tree is a branching graph that shows the evolutionary interrelationships between species and shows the common ancestor. Each node represents the most recent common ancestor of the descendants. The lengths of the branches are time estimates.

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Phylogenetic TreeSpeciation events are shown in this phylogenetic tree. The relationship between ancestor and descendant is based on the number of

h d h i iOld world

kshared characteristics between them.

monkeys

New World Monkeys

Pro-simians

Gibb

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Orangutans

ChimpanzeesHumans

GorillasGibbons



Darwin’s Theory

ReproductionGenetic variationGenetic variationDarwin’s Hypothesis

Reproduction Effects on Evolution

Sir Darwin, can you

First I observed that reproducing organisms will produce more

offspring then the environment can support if all offspring survive to y

tell me about your observations that

lead you to the theory of evolution?

pp p greproduce. This is the struggle for

existence.

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Darwin & Genetic Variation

Sir Darwin how does genetics impact your

I observed that for any given population of individuals there is a range of heritable characteristics.

genetics impact your theory?

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Survival & Inherited Traits

How does an organism’s traits

Survival depends on an organisms inherited traits. If a trait or set of traits enables an organism to survive and

effect a species?g

reproduce that species will survive.

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See these birds? Ability to fly high and hunt will be

helped by big wings in some environments. In other

environments like dense forests smaller wings will

have the advantage.



Darwin’s Hypothesis

The hypothesis states that the attributes leading to a better fit in an environment leads to a greater

chance of survival and leaving

Disproportionate reproductive success within population

members gradually leads to a change in traits of that particular

behind viable offspring. population.

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Support for Darwin’s HypothesisThe theory is tested by looking

into the fossil record and studying taxonomy. By

comparing embryological and anatomical information

How can you test your theory?

anatomical information similarities and ancestry can be

discovered.

Today with modern molecular biology

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molecular biology techniques, it is possible to determine evolution on

the basis of genetics.



Fossils and Evolution Support

Fossils are ancient impressions left by biological forms in sedimentary rocksedimentary rock. These impressions

often reveal the skeletal framework of an extinct

species.

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Fossil RecordsThe oldest fossils record the oldest

species living.

Younger fossils have species with traits common to older fossils plus some additional traits oradditional traits or

similar traits reorganized.

Fossil record

Jurassic "clams"

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indicates that there are shared traits

between ancestors and descendants.

This supports Darwin’s theory.

Cretaceous ammonite

Cretaceous ichthyosaur

Miocene beaver skull

Pleistocene sabertoothed cat

Pleistocene mammoth



Taxonomy Science of Classification

Taxonomy is the science of classification. It is a

hierarchical grouping of i ith d diorganisms with descending

categories having more specific characteristics.

Organization is based on similarity of traits.

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Taxonomic Groupings

Taxonomic groupings are by shared traits among

different species leading to evolutionary relatedness.

The taxonomic grouping support Darwin’s theory that all species within a

group can be shown to be related to one another.

Flowers having similar traits would be grouped together.

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Comparative Taxonomy

Comparative Anatomy, Embryology:

These lines of evidence involve making i f i t t dcomparisons of various structures and

determining the degree of similarity among them.

For Example, flippers, wings, paws, hands.

All have similar bone structures, despite overall external differences - Remember descent with modification

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Genetics & Darwin’s TheoryGenetic evolution refers to

the change in the frequency of a gene or alleles in a

population.

Mechanisms of genetic evolution include: natural

selection, mutation, random , ,genetic drift and gene flow.

Natural selection is the best explanation for genetic evolution Once gene

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evolution. Once gene frequencies change and adaptation due to natural

selection occurs, advantageous genes will be selected again and

again because of directional selection.



Evidence Summary

Types of Evidence

Does the evidence

corroborate Darwin’s Theorycorroborate Darwin s Theory

Fossil Record

Taxonomic Groups

Independent

Yes

Yes

Y

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Independent Traits

Genetics

Yes

Yes

ModernModern Evolutionary Theory

Variations of evolutionary theory.

Environmental effects and selection.



Variations on Evolutionary Theory

My original theory believed that evolution

was a very gradual process. Referred to

Today evidence shows that evolution may be

better characterized bypas gradualism.

better characterized by punctuated equilibrium. A spurt and plateau pattern.

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Darwin

Environment and Evolution

The ecosystem plays a bigger role in stimulating

Yes, an example is dinosaur extinction which is thought

to be a consequence of climate change.

accumulation of new species then was previously

thought.

climate change.

Environmental changes can select for new traits required by that environment and lead

to new species formation.

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to new species formation.



Gene Flow & In Breeding

There are other mechanisms of species modification that have a

minor role in evolution of species. These include: gene flow and non-

Gene flow: individual species breed outside their

tiThese include: gene flow and nonrandom mating (in breeding).

native group.Non random mating: in breeding mating is not

random.

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Question: ReviewThe process in which favorable traits become more frequent.

___________Natural selection

___________

___________

Taxonomy

Fossil record

Punctuated equilibrium

The science of classification.

Evolution is characterized by t d l t thi i

What record supports Darwin’s hypothesis?

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___________Punctuated equilibriumspurts and plateaus, this is known as what?

Minor mechanisms of evolution include these. ___________Gene flow, in-breeding



Darwin’s theory may be

described as

Darwin’s theory may be

described as The major force The major force

Genetic variation can occur when

different

Genetic variation can occur when

different

Learning Summary

described as “descent with modification”.

described as “descent with modification”.

in evolution is natural selection

in evolution is natural selection

different organisms of a

population have different versions of a gene (allele).

different organisms of a

population have different versions of a gene (allele).

The fossil record and molecular biology support Darwin’s

theory.

The fossil record and molecular biology support Darwin’s

theory.

Survival of the fittest means an organism can create offspring

that are viable.

Survival of the fittest means an organism can create offspring

that are viable.

Congratulations

You have successfully completed the core tutorial

EvolutionRapid Learning Center



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