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Devan Lowen

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Transcript of EVOLUTION

Rules of Natural Selection
Evidence of Evolution: Anatomical
Evidence of Evolution: Fossil
Evidence of Evolution: Chemical
What is Evolution?
Natural Selection
= the survival and reproduction of those organisms best adapted to their surroundings. (Fitness)
Natural Selection
Patterns of Evolution
A. Evolution through natural selection is not random.
- those better suited survive.
- the effects of natural selection can add up over time
evolution can occur when different species share similar environments. Analogous structures.
evolution can occur when similar species attempt to move to different environments to avoid competition. Homologous Structures.
D. Beneficial relationships can occur as species interact with each other. (coevolution)
What is Evolution?

Evolution =

the change in the genetic make-up of a species over time.
A. Biodiversity = all organisms found in a specific area.

B. Having Biodiversity ensures that some of these organisms will survive if there is a catastrophe. (Dinosaur extinction story).
: Each species produces more offspring than can survive. Those who are best adapted leave more offspring than those who are not.

Struggle for Existence
: The offspring of each generation must compete for food, water, shelter, etc. Those who do not compete well, die.

: The offspring of each generation are not exactly alike. Differences in traits are called VARIATIONS. (arise over many generations).

Survival of the Fittest
: The organisms that are most likely to survive will reproduce, those who are not likely to survive do not pass on their genes.
1. Contributors to Evolution
Lamarck, Hutton, Lyell, Malthus, Darwin, Wallace
2. Natural Selection
Principals of natural selection
Rules of Natural Selection
Environmental Influences
3. Evidence of Evolution
Anatomical, chemical, fossil, embryological, geographical.
4. Evolution of a Population
Genetic Variation in Populations
Natural selection on traits
Genetic Drift
Factors that lead to evolution
Hardy Weinberg
5. Biodiversity
Patterns of evolution
Due to inheritance (GENETICS) and mutations, organisms change over time (a very very very long period of time)
Evolution is the result of genetic changes that occur in constantly changing environments.

Changes in DNA can occur as a result of mutations which are constantly being generated in a gene pool.

Variation in a species increases the likelihood that at least some members of a species will survive under changed environmental conditions.
Why do you need to learn about evolution?
- Do you get a flu shot every year? Why?
- Why do doctors tell you to finish all of the antibiotic even if you feel better?
Contributors to Evolution
Jean-Baptiste Lamarck

- Use vs. Disuse
Organism's behavior causes changes in certain structures or organs.
These changes were passed on to offspring (acquired traits. Ex. Long neck of giraffes
James Hutton
Charles Lyell

-Proposed the concept of "uniformitarianism" - The geologic processes that shape Earth are uniform over time.
Thomas Malthus

- Proposed that resources in an environment are limited.
- The population size of any organism will be limited by the amount of food, water, sunlight, space, etc.
- the human population will be affected by war, disease, and famine.
Charles Darwin
- Darwin's observations showed him that there were many variations among the species of each of the islands.

- Proposed the concept of gradualism.

is the process by which landforms resulted from slow changes over a long period of time.

- Suggested that the processes that shaped Earth in the past are still shaping Earth in the present.
- Darwin noted that the variations among the species appeared to be best suited (adapted) to the environment to which the organisms lived.
- Darwin traveled on the
HMS Beagle
to the Galapagos Islands in 1831 to study plant and animal life.
-Darwin's careful observations led him to write his book "The Origin of Species"
= differences in a physical trait.
- Galapagos Tortoise (Tall plants = long necks)
Adaptation can lead to a change in genes
Darwin's Finches (Hard Shells = Strong Beaks)
- In 1858, Darwin and Alfred Wallace presented their new Theory of Evolution.

-One of the newest concepts was that of
Natural Selection
Peppered moths- Before and After Industrial Revolution
Principles of Natural Selection
1. Variation within a population is the basis for natural selection.
- Differences arise from different DNA either from inheritance or mutation.

2. Those with a higher
tend to produce many offspring that must compete.

3. Advantages arise in a species when variation makes certain members more adaptive to survive.

4. Future offspring will have traits different from the original ancestor,
Descent with Modification
, as long as the environment is favorable for that trait.
Peacock females pick their mate according to the male’s tail. The ones with the largest and brightest tails mate more often. Today, males that do not have bright feathers are very rare.
Environmental Influences
1. Natural Selection acts on the phenotype of an organism rather than on the genotype.
- How do we know?

2. A change in the environment shows that different traits become more favorable.

3. As certain traits are eliminated from the gene pool, other, more favorable traits are increased, thus changing the overall "look" of the organisms.
Evidence of Evolution: Embryological
Evidence of Evolution: Geographical
- A
is a well supported testable explanation of phenomena that have occurred in the natural world.

Evolution is an attempt to account for all the diversity of life.

-Scientific facts, observations, and hypotheses all make up the Theory of Evolution.

- Evolution is supported by a wide array of scientific evidence.

-If any of this evidence was proven wrong, the theory of evolution must be modified.
- Anatomy = the study of the structure of living things.

- Scientists compare the anatomy of different species to gain support for evolution.

- When different species have similar body parts & structures, we say they are

- Homologous structures show how species may share a more recent common distant ancestor.
- a human's arm
- a cat's foreleg
- a whale's flipper
- a bat's wing
Homologous Structures
Analogous Structures
- Analogous structures show how organisms develop structures that are structurally different but can be used for the same purpose.
Vestigial Structures
- When organisms, however, have a body part that seems to NOT have any function, we call it a
vestigial structure

- Vestigial structures imply that an organism once had a purpose for a structure, however, have evolved to not need it anymore.
- human tail bone
- human appendix.
- Whales and cobras have vestigial hind legs...meaning a distant ancestor may have once walked on land.
The Tailbone:
Grandpa didn’t have a tail, but if you go back far enough in the family tree, your ancestors did. Other mammals find their tails useful for balance, but when humans learned to walk, the tail because useless and evolution converted it to just some fused vertebrae we call a coccyx.
Erector Pili and Body Hair
: Goose bumps aren’t just to alert you of cold. And in many creatures, fear and confrontation cause muscle fibers called erector pili to activate, forcing hairs to stand up and make the animal appear larger and more threatening. That would’ve been useful to your distant ancestors, those hairy beasts!
The appendix? Wisdom Teeth? Why do we have these?
- Chemical Evidence = comparing the DNA different organisms.

- The more closely related an organism is to another, the more similar their DNA sequences.
- Fossils = the imprints OR remains of plants and animals.

- Fossils in older layers are more primitive than those in younger layers.

- Fossils are more likely to form from bones or other hard materials.
- Ex: a jellyfish will be less likely to leave a fossil than a fish.

- Fossils hep scientists trace the evolution of many organisms over time.

-Fossil Record = the biological record of time on earth.
Let's be scientists...Can we hypothesize a story about these turtles?
Human Skull Evolution
Anthropology = the study of man
Dating Rocks and Fossils
- There are 2 main methods used to estimate the age of fossils and rocks:
- Relative Dating
- Radioactive Dating
Relative Dating
Relative dating
= determining the age of a fossil based upon the age and the layer of rock in which it was found.
- fossils found in deeper layers are more likely to be older than fossils found in layers near the surface.
Radioactive Dating
Radioactive Dating
= a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes.

- Radioactive dating measure the "half-life" of certain elements.
= the amount of time it takes for half of an element to decay.
- The most commonly known form of radioactive dating deals with Carbon-14.
Carbon-14: Half - life
Half-Life Practice
Pretend half-life = 2 years
Begin at 0 years with 400 grams of Carbon -14
How much Carbon-14 remains after 2 years?
How much Carbon-14 remains after 6 years?
If there is 25 grams of Carbon-14 left when we date the specimen, how old is the specimen?






- Embryology = the study of developing organisms
- Scientists compare the embryos of different species to see how closely related they are.

- The embryos of vertebrates are very similar in the early stages of development.
- Island species most closely resemble nearest mainland species.
- Populations can show variation from one island to another.
Evolution of a Population
A. Genetic variation in a population increases the chance that some individuals will survive.
- Genetic variation leads to phenotypic variation.
- Phenotypic variation is necessary for natural selection.
- Genetic variation is stored in a population's gene pool.
- Made up of all alleles in a population
- Allele combo's form when organisms reproduce.
B. Allele frequencies measure genetic variation.
- Measures how common the allele is in a population.
- variation comes from several sources: Mutation (passed on only if it occurs in reproductive cells) and recombination (meiosis).

C. Hybridization is the crossing of two different species.
- occurs when individuals can't find a mate of their own species.
- human influence: lygers
Natural Selection on Traits
A. Natural selection determines which individuals will survive and which will be eliminated.
B. Natural selection can change the distribution of a trait.
C. Favorable phenotypes will provide higher fitness for individuals.
1. Alleles associated with favorable phenotypes increase in frequency.
2. Alleles associated with unfavorable phenotypes decrease in frequency.
Directional Selection
1. Certain Phenotypes can be more favorable than another:
ex: Peppered Moths
2. When the trees changed color, the black moth became better suited to survive.
3. The black moths become the favored allele, so the population moves toward the darker phenotype.
Stabilizing Selection
1. A process where the heterozygous alleles are more favorable than either homozygous alleles.
2. The resulting populations contain higher frequencies of heterozygous individuals.
genetic diversity in the population.
Disruptive Selection
1. The homozygous alleles are both favored over the heterozygous alleles.
2. The heterozygous allele is removed from the population due to low fitness.
3. A new species may form from the population by the elimination of the intermediate phenotype.
Relative Frequency
Relative Frequency is the number of times a specific allele appears in gene pool divided by the total number of alleles for that trait.
Ex: 4 TT 6 Tt 2 tt = 24 alleles for this trait

14 T's in the population and 10 t's in the population

T has a frequency of 14/24 = 58%
t has a frequency of 10/24 = 42%
Genetic Drift
A. Genetic Drift occurs when there is a change in gene frequency.

B. There is a decrease in genetic diversity of a population when genetic drift occurs.

C. Two things can cause a population to become small enough for genetic drift to occur:
1. Bottleneck effect = the reduction in the number of organisms.
2. Founder effect = the migration of a few individuals to a new area.
Effects of Genetic Drift
1. A loss in genetic variation.

2. Adaptation becomes a problem when alleles are fixed.

3. Lethal alleles can be carried by heterozygous individuals and may become more common.
Factors that Lead to Evolution
Small Populations:
frequencies of alleles change due to chance. Genetic Drift.
Gene Flow:
the movement of alleles from one population to another changes allele frequency.
new alleles form from changes in DNA which create genetic variation.
Sexual Selection:
certain traits will be more favorable to mate selection, thus increasing the frequency of those alleles.
Natural Selection:
certain traits ill be better adapted to the environment and thus increase in frequency.
Hardy-Weinberg Equilibrium
A. Describes populations that are not evolving.

B. Genotype frequencies stay the same if five conditions are met:
1. Very large population (no genetic drift)
2. No gene flow (emigration/immigration)
3. No mutations (no new alleles)
4. Random Mating (no sexual selection)
5. No natural selection (all traits have an equal chance at survival. )
- Hardy-Weinberg equilibrium is rarely met.
- genetic drift changes allele frequency due to chance alone.
- Gene flow moves alleles from one population to another.
- Mutations are random and produce the genetic variation needed for evolution.
- Sexual selection selects traits that improve mating success.
- Natural Selection selects for traits advantageous for survival.
C. Reproductive isolation will INCREASE the speciation (# of species) of organisms.
- Populations become isolated when there is no gene flow.
- isolated populations adapt to new environments
- genetic differences add up over generations.
1. Behavioral: differences in courtship.

2. Geographic: physical barriers.

3. Temporal: timing of reproduction.
D. Speciation results in an increase in biodiversty as new species emerge with different alleles in their populations.
Geographic Isolation
Even when the riverbed dried up, the beetle populations had changed so much they could no longer interbreed!
Behavioral Isolation
Differences in courtship behaviors such as dancing, vocal calls, colors, patterns... determine whether closely related species mate with each other.
Temporal Isolation
Temporal isolation means 'isolated in time', so this is a mechanism that prevents species from mating because they breed at different times. These differences can be time of day, season, or even different years. Both plants and animals may exhibit temporal isolation, even if species are closely related and live in the same habitat.
E. Species can become extinct when organisms are no longer adapted to their environment.

F. Speciation may occur in patterns such as
adaptive radiation
: decent from a common ancestor.
- Some species benefit when other species die! Ex: dinosaurs to mammals.
G. Evolution can be slow and consistent (gradualism) or it can be fast with long periods of no change (punctuated equilibrium)

H. Some species have not changed/evolved at all because their environment has not changed. - living fossils.
-Example: horseshoe crabs.
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