Unit 1Introduction to Biology Lesson 5 Evolution

John LevasseurSpringfield Central High School

Biology

Introduction Animation

Homework: Read this Chapter

1) Discuss the history of the Theory of Evolution.

2) Explain why Evolution is the key concept and central theme of the science of life.

3) Discuss the four  factors that Darwin recognized  for Evolution via natural selection.

4) What is the significance of Darwin's  Galapagos finches? (This question comes right from the 2007 Biology MCAS.)

Questions to AnswerDaily Problem Set Unit 1 lesson 5

Lesson 5Evolution: One of the Greatest Scientific

Ideas in Human HistoryEvolution is the key concept in biology and one of the greatest ideas in science history. Every unit and every topic that we study in biology relates to the concept of evolution.

•  Galileo's challenging the Aristotelian's view of the universe as up held by the church.

The Greatest Scientific Advances • Newton's Three Laws of Motion.

•Law of Conservation of Mass by Lavoisier•Dalton's Atomic Theory

• Darwin's Theory of Evolution via Natural Selection

• Einstein's Theory of Relativity

Discuss the great scientific

discoveries and why evolution is

the key concept of biology.

A Brief Introduction to the History of the Theory of Evolution

The Ancient Greeks The earliest recorded proponent of evolution was an ancient Greek philosopher Anaximander who lived 2500 years ago.  The great Greek philosopher and father of Western science, Aristotle is credited by Charles Darwin as one who pointed the way toward the explanation of life's unity through natural selection. 

Eighteenth Century Scientists

Georges-Louis, Comte de Buffon (1707 - 1788) was an early scientist who questioned the similarities between apes and humans and offered common ancestry as an explanation.

 Jean-Baptiste Lamarck (1744 - 1829) Charles Darwin himself credited Lamarck's writings and ideas as an early inspiration.

Discuss the history of the

theory of evolution.

A Brief Introduction to the History of the Theory of Evolution, (cont.)

Erasmus Darwin (1731 -1802), Charles Darwin's Grandfather, Erasmus Darwin was a famous poet and naturalist.   Erasmus Darwin's poetry was known for its use of sexual and natural imagery; Erasmus Darwin used poetry to state his view that life had evolved.

Nineteenth Century Scientists who formed the idea of Natural Selection Alfred Wallace (1823 - 1913), thought of natural

selection independently of Charles Darwin.  The first paper published on the topic of evolution by natural selection was jointly written by Darwin and Wallace.

Charles Darwin (1809 - 1882)  The publication of Darwin's book On The Origin of Species revolutionized the scientific view of life. Darwin called his explanation of the way evolution works "Natural Selection".

Discuss both Darwin and Wallace and the story of how each explained evolution as a

function of “Natural Selection”.

Charles Darwin and Natural Selection  After years of observations and experiments, Charles Darwin proposed the Theory of Evolution via Natural Selection.

The Beagle Voyage and The Galapagos FinchesAs a young man, Darwin had sailed around the world on a

voyage of exploration aboard the ship HMS. Beagle collecting fossils and specimens of organism from the different places he visited. 

• Discuss the aspects of Darwin's life story that led

him to the Theory of Evolution.

• Discuss Darwin’s Beagle voyage.

Charles Darwin and Natural Selection  (Cont.)The Beagle Voyage and The Galapagos FinchesOf key importance was the collection of birds, (finches) Darwin made in the Galapagos Islands.Darwin collected a variety of finches from the different Galapagos Islands.Darwin noticed that the form of the beaks from the different species of finches that he collected varied from Island to Island and from feeding habit to feeding habit.Darwin reasoned that the Galapagos Islands, which were geologically new islands, must have been populated by a few common ground finches from the South American mainland.This population of the  common ground finch must have diversified to survive on different types of food in the new environment of the Galapagos Islands.  Adaptation for survival in the Galapagos Islands produced the variety of different species Darwin found there. 

Why was Darwin’s stop at the Galapagos Islands so critical to the development of Darwin’s theory of Natural

Selection? What is the significance of Darwin's finches?

Brief Overview of Natural SelectionDarwin realized the struggle for survival due to the difficulties (or selection pressure) caused by nature must be selecting for heritable trait variations that will allow one organism within a population to out-reproduce the other members of the population.  Darwin published these ideas in his book On The Origin Of Species in 1859. New species must therefore arise by natural environmental selection pressure which forces organisms to adapt to a dynamic or changing environment or become extinct.   

Darwin had been collecting data about this theory since the late eighteen thirties and initially wrote an outline of his idea in 1844.

However, it was not until Alfred Wallace wrote to Darwin with a similar explanation for evolution that Darwin was motivated to write his now famous book the On The Origin Of Species in which Darwin forever changed the way science views life. What is “Natural

Selection”?Who was Alfred R.

Wallace?Explain the Theory of

Natural Selection.Are evolution and Natural

Selection synonymous?

1. Individuals within a population have variation.

2. Some variants are “better” than others.

3. The traits are heritable.4. The “better” individuals

will have more success reproducing and more offspring.

Natural selection is one of the basic mechanisms of evolution along with:

◦mutation◦migration◦genetic drift◦Symbiosis

Imagine a population of beetles:

There is variation in traits.There are green and brown beetles.

There is differential reproduction.Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

There is heredity.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

End result:The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population.

Natural Selection Occurs Because:

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See BioReview for These notesAlso review Comparison between Lamarck and Darwin

1. Competition for survival and opportunities to reproduce between the members of a population.

2. Variation of traits between organisms within a population.

3. The traits that have variation within the population must be heritable traits, that is the traits must be able to be passed to the next generation.

4. Organisms must be able to better adapt to their environment by the inheriting beneficial variations of these heritable traits.

The Four Factors Needed for Organisms to Evolve via Natural Selection

Explain Darwin’s 4 Factors For Natural

Selection.List the 4 factors for

natural selection.

Competition Between Members of a PopulationAn essay by theologian and economist Thomas Malthus helped Darwin see that members of a population compete with each other for survival. Malthus wrote in his, An Essay On the Principle of Population, that humans are in a competition for limited resources and that over-population increases this competition which in turn leads to human suffering and vice.

Darwin recognized that organisms in nature are in a competition for limited resources and that there is a tendency for organisms to over-produce offspring or seeds to ensure survival.

Darwin knew that due to competition between organisms within a population some members of the population will be more successful than other members.

• What is “Malthusian Doom”?• How did “Malthusian Doom” help both Darwin and Wallace

see that competition within a population lead to natural selection?

• Where do we see Malthusian Doom today?• What are the strengths and weaknesses of the idea of

Thomas Malthus?

Competition Between Members of a Population, (cont)

Fitness is the term Darwin used to describe the ability to compete for resources and opportunities to reproduce.

Competition means there will be winners and losers.

For Darwin the "winners" were those organisms in a population better suited for survival in a particular environment which allowed them to have more of their offspring survive than a member of the population less suited for survival.

The fitness of an organism determines the ability to out-compete similar organisms in the same population for survival and reproduction.

Competition for survival between members of a population is the first factor needed for evolution via natural selection.

What is “fitness” in a Darwinian sense?

Variation Between Organisms Within a Population

 It is clear to all observers of nature that organisms of the same species are not identical.  

Examples: No two oak trees, (Quercus alba), nor any two whitetail deer, (Odocoileus virginianus), or any individuals of other species are identical. 

Variation of any trait between members of any population will always graph into a normal distribution of the trait (a bell-curve) if you sample enough members of the population. 

Here is an amazing fact.

• What is variation?• Why will any trait graph

into a bell curve?

Variation Between Organisms Within a Population, (cont)Let’s see if we can test the statement that variation of any trait between members of any population will always graph into a normal distribution of the trait (a bell-curve) if you sample enough members of the population. Think of our population as Central High School sophomoresYou can pick any random trait, like height and graph that trait.Is there variation in the height of the sophomores?

Of course there is.

There will be a tallest and a shortest and every one else in-between with the majority of sophomores having some average height.How tall will the tallest be? How tall will the shortest be?What will be the average height?

Amazing! The data of our sophomores' heights fits this graph. 

Explain this demonstration of a trait always graphing into a

bell curve.

Variation Between Organisms Within a Population, (cont)

Here is a graph actually generated from data collected on the beak depths of a population of finches in the Galapagos Islands. 

Remember that Darwin had collected finches from the Galapagos islands, and these birds inspired him to think that the variety of finch species found in the Galapagos was due to variations of one species of finch evolving into a variety of similar species.

Here we see a the results of survey of one species of finch from those same islands.

Notice how real data does not fit perfectly to the mathematical ideal, but the data does follow the pattern. 

Explain this demonstration of Darwin’s Finches beak size graphing

into a bell curve.

Variation Between Organisms Within a Population, (cont)

Variation within a population not only exists but it can be measure and graphed.

Variation between members of a population is the second factor needed for evolution via natural selection.

Organisms within a population have variations.

Sometimes a variation helps an organism obtain necessities for survival within the organisms’ environment.

Other times a variation limits an organism’s ability to obtain the necessities of life. 

While most times a variation neither helps nor hurts an organism’s ability to obtain necessities. 

Discuss how variation within a population can lead to natural

selection?

 Heritable TraitsOrganisms have the means of passing traits from one generation to the next.

The variations between organisms within a population are inheritable traits and are passed on from one generation to the next.If an organisms within a population has a heritable variation that increases that organism’s change for reproduction. Then generation after generation that variation will become.

Note that Darwin recognized this fact but did not know how the inheritance of traits worked.  This was not understood until after Mendelian genetics was adapted.

Heritable traits is the third factor needed for evolution via natural selection.

• Explain why heritable traits is one of Darwin's prerequisites for

Natural Selection.

Adaptation to Environment Before we consider the ability of populations of organisms to adapt naturally to their environment , we will consider the ability of humans to select for traits in agricultural crops and animals.

Artificial Selection Another observation that sparked Darwin's thinking was the breeding

of farm animals and agricultural crops.  Darwin was a pigeon breeder and was interested in livestock and dogs that had been bred by humans.  Darwin knew that farmers select breeding mates by choosing traits that the breeder wants to enhance in the next generation.

Darwin called the selection of traits done by breeders artificial selection. 

Explain artificial selection.

Adaptation to Environment, (cont.)Notice the  variation  in these two types of dogs, (Canis domesticus,  aka. Canis lupus familiaris).

Dogs were bred by humans from the wolf, (Canis lupus),Consider if these dogs would be in the same species if they were in nature and not bred by humans from the wolf.

What differences in the two dogs above do you notice?  Remember both were bred by humans from a common ancestor, the wolf (Canis lupus)Would these two dogs be the same species in nature?  Would they mate to produce fertile offspring?

Darwin questioned that if humans can select traits and breed animals to be better adapted to some human want such as gentle disposition, more meat, better eggs; why can't nature select for traits better suited for survival in a particular environment, such as warmer coat, better camouflage, beak form better suited for acquiring food?

Explain why these dogs bred by human would be separate species if found in nature and not artificially

selected for.

Natural Selection◦ Darwin realized the struggle for survival

due to difficulties (or selection pressure) caused by nature must be selecting for trait variations that will allow one organism within a population out-reproduce the other members of the population.

◦ New species must therefore arise by natural environmental selection pressure which forces organisms to adapt to a dynamic or changing environment or become extinct.   

Natural selection is a mechanism of change in populations that allows for adaptation to better survive in a particular environment. Nature selects the trait by chance and by reproductive success, (fitness).

A population’s change over time through adaptation to a dynamic environment is the fourth factor needed for evolution via natural selection.

Adaptation to Environment, (cont.)

Animation

Why do organisms

need to adapt to

their environmen

t?

Explain stabilizing, disruptive and directional selection.

Animation

Adaptation to Environment, (cont.) If the heritable trait variations within a

population  are normally distributed then there must be three possible changes to the population due to natural selection.

Recall that all random variations of any trait can be measured and graphed in a bell curve.

The three forms that nature can select for on a population are:◦ Stabilizing: all members become more

alike because the extremes of variation disappear.

◦ Disruptive: members of one population diverge because the average form of the trait is detrimental for survival.

◦ Directional: members of a population appear very different over time since one extreme is more beneficial for survival than the other extreme driving the population to have a new average for the trait.

Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling.◦ One gene may have multiple forms, called alleles.

Genetic drift is an evolutionary process, which leads to changes in allele frequencies over time. ◦ Genetic Drift may cause gene variants to disappear completely, and

thereby reduce genetic variation. In natural selection gene variants become more common or less

common depending on their reproductive success.◦ The changes due to genetic drift are based on happenstance and not

driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.

The effect of genetic drift is larger in small populations, and smaller in large populations.◦ Luck effects small populations more than large populations

Genetic Drifthttp://en.wikipedia.org/wiki/Genetic_drift

http://en.wikipedia.org/wiki/Founder_effect

The Founder Effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

As a result of the loss of genetic variation, the new population may be distinctively different, both genetically (DNA) and phenotypically (appearance), from the parent population from which it is derived.

In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species.

The founder effect is a special case of genetic drift

Founder Effect (the Bottle Neck) See Tutorial

We see bottlenecks

in endangered

species, migration to

new land masses like

Hawaii or the Galapagos or Pennsylvania

.

Darwin's Theory Modified to Modern Synthesis  

The Modern Synthesis between Darwin's Natural Selection and Contemporary Understanding of DNA

EcologyIn Darwin's day, biology, geology, and environmental science were all wrapped into one study called "Natural History". Today "Natural History" would be called "Ecology" in which we study how organisms interact with each other and their environments.  Our understanding of how organisms interact and depend on each other and the environment has grown greatly since Darwin's era.   Darwin used competition as the interaction driving evolution; however, today scientists look at other interactions, such as cooperation, as a relationship that drives evolution.

 BiochemistryThe understanding of the chemistry of living things has been incredibly expanded since the time of Darwin. The discovery of DNA and how that molecule codes for the proteins that cause the variations between members of a population alone stands as a great advancement in science since Darwin. • What are ecology and

biochemistry?•What is the Modern Synthesis?Animation

Homework:Read this Chapter

Darwin's Theory Modified to Modern Synthesis, (cont.)

Cell BiologyA great understanding of the cell and cell organelles have allowed scientists to explain the origins of common ancestry more fully.

GeneticsDarwin did not know the mechanism of how organisms inherit their traits, genetics.

Anatomy and PhysiologyDiscoveries in the structure and development of organisms shine light on the unity of life. 

Knowledge From the Other Natural Sciences that Relate to EvolutionFossil discoveries and the ability to date fossils have added support to Darwin’s Theory.Note how ecology, biochemistry, cell biology, genetics, anatomy and evolution are our remaining units this year.

We can think of the class as a cycle.Talk about what we’re going to talk about, talk about it then talk about what we talked about

• What are: cell biology, genetics,

anatomy and physiology?

• What will we be studying this year?

This Biology Class as a Cycle

Introduction

Ecology

Chemistry of life

CellsGenetics

Anatomy and

Physiology

evolution

Explain how this biology

class can be thought

of as a cycle.

The rest of our course will be spent explaining in greater detail this narrative on evolution:DNA is a molecule that stores information chemically about how to build proteins; proteins are the molecules in living things that really do the work of life.  DNA has sections of information known as genes that hold the information for just one protein.  DNA and genes can change through copying mistakes called mutation, which cause changes in proteins. The changes in the proteins cause changes and variations in organisms.  Sometimes those variations will be a benefit to the organism.  Other times a variation will be a detriment to the organism.  Most times a variation will neither help nor hurt an organism. Organisms in a population compete for resources and opportunities to pass on genes (have offspring).  Those organisms within a population with the genetic phenotype that produces the protein variations that benefit or increase the organism’s fitness (ability to gather resources and on pass genes), will have more offspring than those organisms with variations that are less favorable for survival in their environment.The beneficial variations due to increased number of the genes that cause those variations will become more frequent in the next generation.Evolution happens as a population’s genes and the gene frequencies change over time.  A change in genes means a change in proteins, which could allow for changes in the organism's biochemistry or appearance. These changes have been the result of nature favoring one type of gene, (protein) over another for survival in a certain environment.  Evolution causes organisms to become better adapted for survival in  an environment. 

Explain this paragraph in your own words.

Questions to Ponder from: Lesson 5

Are biology and science the same thing? What is science?  What are the studies and explanations in science limited to? Why can the study of science be a paradox?   What is the key concept of science?  What does the word dynamic mean? What things in nature are dynamic?  What is biology? What is the key concept of biology?Should we include supernatural topics in the study of natural science? Who was Stephen Jay Gould and what is his principle of NOMA?Who was Charles Darwin? Was Darwin the first person to propose that living things evolve? What is artificial selection?What is natural selection?What is the HMS Beagle and how does it relate to the topic of evolution?What are the four factors need for evolution via natural selection?What is the significance of Darwin's finches from the Galapagos islands?

Answer at least three of these questions.

Mutation

Evidence for Evolution: Fossil

Evidence for Evolution: Developmental

Evidence for Evolution: Genetic