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
e o
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!