Flies in the Barnyard: On a sheet of paper write 1-2 sentences explaining why you think this happened

A farmer was working with dairy cattle at an agricultural experiment station. The population of flies in the barn where the cattle lived was so large that the animals’ health was affected. So the farmer sprayed the barn and the cattle with a solution of insecticide A. The insecticide killed nearly all the flies.

Sometime later, however, the number of the flies was again large. The farmer again sprayed with the insecticide. The result was similar to that of the first spraying. Most, but not all of the flies were killed.

Again within a short time the population of flies increased, and they were again sprayed with the insecticide. This sequence of events was repeated five times; then it became apparent that insecticide A was becoming less effective in killing the flies

Evolution

Chapters 15 - 17

Important People in Evolution

James Hutton (1785) – Proposed that Earth was shaped by geological forces that took place over extremely long periods of time. He estimates the Earth to be millions of years old.

Charles Lyell (1833) - wrote Principles of Geology

Thomas Malthus (1798)

Predicted the human population would grow faster than the space and food supplies needed to sustain them.

Jean-Baptiste Lamark (1809)

Proposed that organisms changed over time due to use and disuse of certain organs/parts. The traits that were “used” in an organism’s lifetime could be passed on to their offspring.

His theory was flawed!

Lamarck v/s Darwin

Alfred R. Wallace (1858)

Darwin’s old assistant; challenged Darwin’s thinking, and wrote his “own” essay on the theory of evolution.

HE was the reason Darwin reported his research!!!

All of these ideas influenced Darwin’s thinking…

Charles Darwin (1831) – Set sail on the H.M.S. Beagle.

Voyage provided him with much of the data and evidence that lead to his theory of evolution.

Darwin’s “Theory of Evolution” would turn the scientific world upside down!!!!

What did Darwin Observe? Extreme diversity

existed among plant and animal species around the world.

The organisms found within a certain area were well suited to survive in that environment.

Living organisms he observed greatly resembled fossils that he found on his voyage.

The Galapagos

Islands

This tiny group of islands influenced Darwin the most!

Although the islands were close together, the climates and environments differed greatly.

Similar organisms found on different islands had varying characteristics.

Examples: Giant Galapagos Tortoises

with varying shell shape. Darwin’s Finches – beak

shape differed among the birds.

Darwin Presents his Theory of Evolution…

1859 – Darwin published his work: On the Origin of Species

What is a species? A group of organisms that can interbreed and produce fertile offspring.

What is natural variation? Differences among individuals of a species.

Humans had been employing “artificial selection” for many years! Selection by humans for breeding of useful traits from the

natural variation among the organisms (remember selective breeding )

Adaptations & Darwin’s Evidence

Day 2

Evolution by Natural Selection Struggle for Existence

Survival of the “Fittest” – Fitness results from adaptations that give an organism advantages for survival. The most “fit” organisms will survive and reproduce; passing along the advantageous characteristics to their offspring. These changes can only be seen after many generations!

Adaptation – a trait that makes living things betterable to survive in their surroundings.

Three Types of Adaptations

Physiological Adaptations - traits that involve the internal functions or chemistry of an organism (ex: weeds resistant to pesticides, bacteria resistant to antibiotics, etc.)

Think…”Chemical” or “enzyme”

Structural Adaptations

Structural Adaptations – traits that involve the physical structure or anatomy of an organism (ex: quills of porcupine; mimicry, camouflage, etc

Some other structural adaptations are subtle…..MIMICRY

THE MOTH, LEAF INSECT, & STICK BUG ARE GREAT EXAMPLES OF MIMICRY!!!

Mimicry enables one species to resemble another species.

Behavioral Adaptations

Behavioral Adaptations – inherited traits that help an organism survive and reproduce in a given environment; a behavior, response, or action (ex: living in hunting groups)

Descent with Modification As organisms change over time; they

become different, resulting in many varied species. This illustrates “common descent.” All living things have a common ancestor.

Ex: Owl White Mouse Black mouse!

So…

All species – living and extinct –were derived from common ancestors.

This concept is called COMMON DESCENT. Descent with modification + common descent

leads to the conclusion that there is a single “tree of life” that links all living things on Earth”

So, What is the proof all this happens?

Darwin argued that living things have been evolving on Earth for millions of years and the Evidence Used to Support his Evolution Theory was based on: Fossil Record Geographic Distribution of living species Homologous Body Structures Similarities in early development Biochemical Evidence

1. Fossil Record - dead remains of an organism that has left an imprint in sedimentary rock and/or clay.

2. Geographic Distribution of Living Species -Species evolve differently based on where they live.

3. Homologous Body Structures – traits from a common embryo (one of the first stages of development).

5. Biochemical Evidence – common DNA sequences that relate to GENES!!!

4. Similarities in Early Development

Vestigial Organs –organ or structure you no longer need (or has no known function ex: appendix).

Homologous Structures vs. analogous structures (add to your notes…sorry I forgot to add in )

Homologous structures are similar structures occurring in different species that are believed to be derived from a common ancestor.

Analogous structures are similar structures occurring in different species that are believed to be the result of convergent evolution.

The Three Types of Natural Selection

Evolution & Genetics

Darwin had a disadvantage when he developed his theory of evolution…he did not understand the mechanisms of heredity.

Today, we understand how genes, heredity, and evolution all tie together.

Single-Gene Traits vs. Polygenic Traits Both lead to evolution, but polygenic traits

(wide variety of phenotypes possible) lead to a more complex process of natural selection.

Three effects of selection on a characteristic:

1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection

Directional Selection

When individuals at one end of the population curve have higher fitness than individuals in the middle or at either end of the population curve.

Causes entire curve to move as character trait changes

Ex: beak size of Galapagos finches peppered moths

antibiotic resistance

Directional Selection

Food becomes scarce.

Key

Low mortality, high fitness

High mortality, low fitness

Directional SelectionSection 16-2

Stabilizing Selection

When individuals near the center of the curve have higher fitness than individuals at either end of the curve

Intermediate forms of a trait are favored and alleles that specify extreme forms are eliminated from a pop.

Counteracts the effects of mutation, gene flow, and genetic drift – preserves the most common phenotypes.

Ex. Weight of human babies at birth

Key

Per

cen

tag

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f P

op

ula

tio

n

Birth Weight

Selection against both

extremes keep curve narrow and in same

place.

Stabilizing SelectionSection 16-2

Low mortality, high fitness

High mortality, low fitness

Stabilizing Selection

Disruptive Selection When individuals at the upper and lower ends of

the curve have higher fitness than individuals near the middle.

Forms at both ends of the range of variation are favored and intermediate forms are selected against

– selection creates two, distinct phenotypes

Ex: Bird beak size – no middle sized seeds, only large seeds and small seeds; thus, small and large beaks are favored

Disruptive Selection

Largest and smallest seeds become more common.

Nu

mb

er o

f B

ird

sin

Po

pu

lati

on

Beak Size

Population splits into two subgroups specializing in different seeds.

Beak Size

Disruptive Selection

Nu

mb

er o

f B

ird

sin

Po

pu

lati

onKey

Low mortality, high fitness

High mortality, low fitness

Section 16-2

EVOLUTION & RESISTANCE

Evolution of Insecticide Resistance

1. By spraying crops with poisons to kill insects, humans have unwittingly favored the reproductive success of insects with inherent resistance to poisons.

2. Resistant individuals survive and reproduce, passing the gene for resistance to offspring.

3. Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow.

The Evolution of Drug Resistant HIV

Researchers developed numerous drugs to combat HIV, but using these medications selects for viruses resistant to the drugs A few drug-resistant viruses may be present by

chance at the beginning of treatment The drug-resistant pathogens are more likely to

survive treatment and pass on the genes that enable them to resist the drug to their offspring

As a result, the frequency of drug resistance in the viral population rapidly increases

Antiviral Resistance

Evolution & Genetics

Day 4

Genes & Variation

While developing his theory of evolution, Darwin did not know how heredity worked

Without understanding heredity, Darwin was unable to explain 2 important factors:

1. The source of variation central to his theory

2. How hereditable traits were passed from one generation to the next

Today, genetics, molecular biology, and evolutionary theory work together to explain how evolution takes place

Gene Pools

A gene pool is the combined genetic information of all the members of a particular population Recall that a population is a collection of

individuals of the same species in a given area which share a common group of genes

The relative frequency of an allele is the number of times that allele occurs in a gene pool compared to the number of times other alleles occur

For example…

Gene pool would be a collection of all of the options.

R.F. would be how often a particular gene shows up

Sources of Genetic Variation

The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction A mutation is any change in a sequence of DNA Most inheritable differences are the result of gene

shuffling that occurs during sexual reproduction

Genetic Drift

In addition to natural selection, genetic drift is a way by which allele frequencies can change

In the real world, population sizes fluctuate Because populations fluctuate in size, sometimes there can

be changes in allele frequencies due to random chance These changes are called random genetic drift

In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by change Over time, a series of chance occurrences of this type can

cause an allele to become common in a population

The Power of Genetic Drift

Genetic drift is a powerful force when a population size is very small

Can and does lead to allele fixation

Depends on starting frequency (which allele becomes fixed)

Consequences of Genetic Drift Consequences of genetic drift:

Can and does lead to fixation of alleles Effect of chance is different from population to

population Small populations are effected by genetic drift

more often than larger ones Given enough time, even in large populations genetic

drift can have an effect Genetic drift reduces variability in populations by

reducing heterozygosity

Real World Examples of Genetic Drift

The Bottleneck Effect Occurs when only a few

individuals survive a random event, resulting in a shift in allele frequencies within the population

Small population sizes facilitate inbreeding and genetic drift, both of which decrease genetic variation

Real World Examples of Genetic Drift

The Founder Effect Occurs when individuals

from a source population move to a new area and start a new population

This new population is often started by relatively few individuals that do not represent the population well in terms of all alleles being represented

So…

What determines which variants survive the event or get to the new location?

Random chance

Genetic drift has the largest effect on small populations (10-100 individuals)

Speciation

Day 6

Speciation

Isolating Mechanisms = Reproductive Isolation = Formation of a Species

In other words, Isolating mechanisms are objects that separate species and prevent them from reproducing.

By isolating a species a NEW species can be formed!!!

3 Major Types of Isolation:

Behavioral Isolation – Two separate species are capable of interbreeding, but they do not because of behavioral differences.

Example Meadowlarks, different songs to attract mates; courtship (dating)

Geographic Isolation – When one species becomes separated by some barrier (river, mountain, road, mall, etc.) they may develop into two distinct species over time.

Example Squirrel population split by Colorado River 10,000 years ago

Temporal Isolation…

This mechanism occurs when species reproduce at different times (different mating times) or seasons.

Example Orchids in the rainforest, only release pollen 1 day!