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Charles Darwin and Evolution

Lecture notes for a high school CP biology course on Darwin and Evolution. Credits to Miller and Levine Biology Text

Mrs. Mccoy

on 1 May 2015

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Transcript of Charles Darwin and Evolution

Charles Darwin and Evolution
Darwin's Epic Journey
Born in England in 1809
Studied in college at 16 to be a doctor
Attended Christ College to pursue a career as a naturalist and priest
Avid collector of flora and fauna
Astounded by variety of Life

Darwin’s Epic Journey
Darwin sailed on a ship called the
for a 5-year voyage mapping the coastline of South America. Darwin planned to collect specimens of plants and animals on the voyage.

This would be one of the most
important scientific voyages in history.
Species Vary Globally
Darwin noticed that places around the world that had similar habitats often had similar animals.

Darwin also noticed that different, yet related, animal species often occupied different habitats within a local area.
Rhea, South America
Ostrich, Africa
Emu, Australia
According to Darwin's observations, how likely would it be that similar squirrel-like species would be found in other similar habitats to ours? (like out west or in Europe)
Species Vary Locally
Darwin noticed that different, yet related, animal species often occupied different habitats within a local area.

For example, Darwin found two species of rheas living in South America: one in Argentina’s grasslands and the other in the colder, harsher grass and scrubland to the south.
Species Vary Locally
Other examples of local variation came from the
Galápagos Islands
, Pacific coast of South America.

These islands are close to one another, yet they have different ecological conditions. Several islands were home to distinct varieties of giant land tortoises.

Darwin saw differences among the tortoises
that inhabit the islands, specifically, that the
tortoises’ shells varied in predictable
ways from one island to another.
Greater Rhea
Lesser Rhea
Species Vary Locally
Darwin also observed that different islands had different varieties of mockingbirds, all of which resembled mockingbirds Darwin had seen in South America.

In addition, Darwin noticed several types of small brown birds on the islands with beaks of different shapes. He didn’t consider these smaller birds to be unusual or important—at first.
Species Vary Over Time
Darwin also collected
, which are the preserved remains or traces of ancient organisms.

Darwin noticed that some fossils of extinct animals were similar to living species.
Darwin wondered if the armadillo might be related to the ancient glyptodont.

He wondered: Why had glyptodonts disappeared? And why did they resemble armadillos?
Putting the Pieces of the Puzzle Together
On the voyage home, Darwin thought about the patterns he’d seen...

The Galápagos mockingbirds turned out to belong to three separate species found nowhere else. And the little brown birds were actually all species of finches, also found nowhere else, though they resembled a South American finch species.

The same was true of Galápagos
tortoises, marine iguanas, and
many plants that Darwin had
collected on the islands.
Putting the Pieces of the Puzzle Together
Darwin began to wonder whether different Galápagos species might have evolved from South American ancestors.

He spent years actively researching and filling notebooks with ideas about species and evolution.

The evidence suggested that species are not fixed and that they could change by some natural process.
What differences do you see between these tortoise shells?
What ecological differences in the tortoises habitats may have selected for these differences?
Darwin Presents His Case
Darwin knew that his theory was radical, so he wanted to gather as much evidence as he could to support his ideas before he made them public.

In 1858, Darwin reviewed work containing similar ideas about evolution by
Alfred Wallace
, a naturalist working in Malaysia. Not wanting to get “scooped,” Darwin decided to move
forward with his own work.

Wallace’s essay was presented with some
of Darwin’s observations at a scientific
meeting in 1858. The next year,
Darwin published his first complete
work on evolution:
The Origin of Species
After his voyage, Darwin wrote
up a complete draft of his ideas about natural selection, but he put the work aside and didn’t publish it for another 20 years.
Why do you think he waited so long to publish such ground breaking findings??
Under what conditions does natural selection occur?
The Struggle for Existence
If more individuals are produced than can survive, members of a population must compete to obtain food, living space, and other limited necessities of life.
Variation and Adaptation
Individuals have natural variations among their heritable traits (phenotypes), and some of those variants make an organism better suited to life in their environment than others.

Any characteristic that increases an organism’s ability to survive and reproduce is called an
Adaptations can involve
body parts
or structures, like a tiger’s claws;
, like those that make camouflage or mimicry possible; or
physiological functions
, like the way a plant carries out photosynthesis.
Many adaptations also involve behaviors, such as the avoidance strategies prey species use.
Survival of the Fittest
describes how well an organism can survive and reproduce in its environment.

Individuals with adaptations that help it survive and reproduce and are said to have
high fitness

Individuals with characteristics that are
NOT well-suited to their environment
either die without reproducing or leave
few offspring and are said to have
low fitness
For example, a crane will display defensive behavior to scare off a predator.
Look how big and scary I am!!
ex. retractable claws
This difference in rates of survival and reproduction is called
survival of the fittest
. In evolutionary terms, survival means reproducing and passing adaptations on to the next generation.
Natural Selection
The process by which organisms with variations most suited to their local environment survive and leave more offspring.
Natural Selection
This hypothetical population of grasshoppers changes over time as a result of natural selection. Explain what is happening in each picture in relation to the caption below.
Common Descent
According to the principle of common descent, all species—living and extinct—are descended from ancient common ancestors.
Just as well-adapted individuals survive and reproduce, well-adapted species also survive over time. Over many generations, adaptation could cause successful species to evolve into new species.
Common Descent
Darwin based his explanation for the diversity of life on the idea that species change over time.

This page from one of Darwin’s notebooks shows the first evolutionary tree ever drawn. This sketch shows Darwin’s explanation for how descent with modification could produce the diversity of life.

A single “tree of life” links all living things
Let's Review
According to Darwin's findings, what are the 3 ways in which species vary?
Evidence of Evolution
Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors.
Two biogeographical patterns are significant to Darwin’s theory:
Closely Related but Different
Distantly Related but Similar
On the other hand, similar habitats around the world are often home to animals and plants that are only
distantly related

Darwin noted that similar large, flightless birds inhabit similar grasslands in South America, Australia, and Africa.

Differences in body structures among those animals show that they evolved from different ancestors. Yet, similarities among those animals provide evidence that similar environmental pressures had caused distantly-related species to develop similar adaptations.
For example, natural selection produced variation in shell shape among the giant land tortoises that inhabit the islands.
The Age of Earth
Evolution takes a VERY long time.
Recent Fossil Finds
Since Darwin's time, paleontologists have discovered hundreds of fossils that document intermediate stages in the evolution of many different groups of modern species.

Comparing Anatomy and Embryology
Evolution explains the existence of homologous structures adapted for different purposes as the result of descent with modification from a common ancestor.
For example, the front limbs of amphibians, reptiles, birds, and mammals contain the same basic bones.
Homologous Structures
Darwin proposed that animals with similar structures evolved from a common ancestor with a basic version of that structure.

Structures that are shared by related species and that have been inherited from a common ancestor are called
homologous structures
Homologous bones, as shown by color-coding, support the differently-shaped front limbs of modern vertebrates.
Analogous Structures

Body parts that share a common function, but not structure, are called
analogous structures
. The wing of a bee and the wing of a bird are analogous structures.
Vestigial Structures

Over time, natural selection in the Galapagos islands produced variations among populations that resulted in
different, but closely related
, island species.
Not all homologous structures have important functions.

Vestigial structures
are inherited from ancestors, but have lost much or all of their original function due to different selection pressures acting on the descendant.
In whale ancestors, the pelvis played a role in walking. However, as the whale's ancestors adapted to life at sea, this function was lost.
Vestigial Structures
The appendix in humans or the legs of a three-toed skink are examples of vestigial structures.
Why would an organism possess structures with little or no function?
One possibility is that the presence of a vestigial structure does not affect an organism’s fitness. In that case, natural selection would not eliminate it.
The same groups of embryonic cells develop in the same order to produce many homologous tissues and organs in vertebrates (animals with back bones).

Similar patterns of
embryological development
provide further evidence that
organisms have descended
from a common ancestor.
Genetics and Molecular Biology
For example:
Life’s Common Genetic Code
All living cells use information coded in DNA and RNA to carry information from one generation to the next and to direct protein synthesis.
Similar genetic code is indisputable evidence that all living organisms descended from common ancient ancestors.
These snails are all the same species of Cuban Tree Snails
What characteristics to all these snails have in common?
What variations do you see?
What controls an organism's traits?
While on the Beagle, Darwin Observed 3 ways that species vary...
The strongest evidence supporting evolutionary theory comes from genetics.

We now understand how genetic mutations occur during sexual reproduction to produce the heritable variation on which natural selection operates.
Homologous skeletons in primates

Intro to Evolution
What scientific explanation can explain the diversity of life?
Evolution is the slow gradual change of allele frequencies in a population over time
Evolution is not how a tadpole sprung legs

Evolution is an idea that will allow you to grasp and understand things better; it can be applied to all things
The Galapagos Islands
Small Group of Islands 1000 km West of South America
Island species varied from mainland species & from island-to-island species
Darwin used the phrase, “Descent with modification” to explain his theory
Evolution is only used once in the book at the very end as “Evolve” meaning to change over time

Essence of Darwin's Ideas
Darwin's Tenants

1. Variation within a Population

2. The Struggle for Existence

3. Differential Survival

4. Differential Reproduction

Variation within Populations
Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.

Unique Adaptations in organisms

Species Not Evenly Distributed
Ex: Australia, Sugar Glider
North America, Flying Squirrel

Only the most fit survive.
Ex: warblers
Feed in different
Heights of tree

Due to variation in the population
Some organisms have traits that will allow them to survive at higher rates than others within the environment
Ex: Bumpus Sparrow Studied small, medium and large wing length in sparrows Concluded that medium wing length birds has higher survival

Differential Variation
Differential Reproduction
Due to differential survival
Adaptation that allow for more survival become more common in the population

Ex: Snail shell coiling
If those snails have medium coiled shells survive more, then that characteristic will be passed to more offspring.

Driving force for evolution

Evolution by natural Selection Concepts:
The Struggle for Existence
Survival of the Fittest
Descent with Modification

Artificial Selection
Nature Provided The Variation Among Different Organisms
Humans Selected Those Variations That They Found Useful
Close resemblance between two or more species that gives one, both or all a selective advantage ( increase fitness)
Behavioral or physical
Two Types
Harmless organism looks like a harmful organism.
Associative learning exercise for the attacking species. They become very scared to attack organisms that look similar to that bad experience.
This increases survival rates for the mimickers.
Hover flies mimic bees
Long horned catus beetle
Behaves like a circus beetle. Circus beetle raises abdomen and releases a noxious chemical when threatened by predators.

A harmful organism looks like another harmful organism.
Monarch and Viceroy butterfly

The fossil record is incomplete. the nature of how a fossil is made (ONLY under certain conditions) and the fact that some are still undiscovered in the dirt or at the bottom of bodies of water.
Population Evolution
When Darwin developed his theory of evolution, he did not understand how heredity worked. This left him unable to explain two things:
a. source of variation
b. how inheritable traits pass from one generation to the next
In the 1940’s, Mendel’s work on genetics was “rediscovered” and scientists began to combine the ideas of many branches of biology to develop a modern theory of evolution. When studying evolution today, biologists often focus on a particular
. This evolution of populations is called

Gene Pool
Allele Frequency

What are four criteria for a group of individuals to be considered a population?

Gene Pool
combined genetic info. for all members of a population
One form of a gene
Allele Frequency
# times an allele occurs in the gene pool compared to other alleles (percent)
Ex: 70% Allele B 30% Allele b

Allele Frequency of Pasta
There are three phenotypes of pasta shapes in this container. What are they?

PP is _________
pp is __________
Pp is _________

How many alleles are needed to code for a trait? Where do they come from?

Calculate Allele Frequency of 20 Pasta Shapes
Phenotypic Frequency: total number of each phenotype/20

Allele Frequency: total number of each allele/ 40

How can you tell if a Population is Evolving?
If the allele frequency changes from one generation to the next the population is
If the allele frequency is not changing from one generation to the next, then the population is in
Hardy-Weinberg Theorem
to find this out

Hardy-Weinberg Theorem
Set of equations used to determine if a population is changing or not due to allele frequencies
A population at equilibrium must follow Hardy-Weinberg rules: (Lets use our Alleles for pasta)
The frequency for B = p
The frequency for b= q

The frequency for both alleles = 100%
Use the equation p+q=1
Where p is dominant allele percentage and q is ________.

Finding out our ps and qs
Hardy-Weinberg Equation
The frequency of all three genotypes is given by:
p2+ 2 pq+q2=1 or 100%

q2= ss

This equation refers to the percent composition of each allele per number of organisms in the population

Checking your Work
How do we know it adds to 1?

p=.5 q=.5
AA pXp= (.5)(.5) = .25
Aa 2pq= 2(.5)(.5)= .5
aa qXq= (.5)(.5)= .25

5 Conditions must be met for a population to be at equilibrium

1. Large population must exist
2. No migration inside or out of the population
3. No mutations are occurring
4. Random mating
5. All members survive and reproduce

3 Types of Natural Selection
1. Directional
2. Stabilizing
3. Disruptive
Ways in which traits change
over time
Directional Selection
Individuals at one end of the curve have higher fitness so evolution causes increase in individuals with that trait

What do the red arrows indicate?
Stabilizing Selection
Individuals at the center of the curve have highest fitness.

Selection operates against extremes and favors intermediate phenotype

Example: coiling size in snails

What do arrows indicate?
Disruptive Selection

Individuals at both ends of the curve survive better than the middle of the curve.

Selection against intermediate phenotypes and favor extreme phenotypes

Ex:If the forest contains dark-colored spruce trees and light-colored birch trees, it is beneficial for a butterfly to be either dark or light in color.
Let's Review

What is the purpose of using Hardy-Weinberg?
Darwin didn't know the source of variation in a population of organisms.
Through learning about Hardy-Weinberg what are things that cause variation in a population?
The formation of new biological species, usually by the division of a single species into two or more genetically distinct ones.

What is a species?
What is some evidence we can use to determine if a species divides into two distinct ones?

3 Causes Speciation
1. Geographic Isolation
2. Behavioral Isolation
3. Temporal Isolation
Geographic Isolation

Two populations separated by a geographic barrier; river, lake, canyon, mountain range.

Example: 10,000 years ago the Colorado River separated two squirrel populations.
Behavioral Isolation

Two populations are capable of interbreeding but do not interbreed because they have different ‘courtship rituals’ or other lifestyle habits that differ.

Ex: Male birds sing a matting song that females like, East and West have different songs. Females only respond to their subspecies song.

Temporal Isolation

Populations reproduce at different times

Ex: Northern Leopard Frog & North American Bullfrog

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