Transcript Evolution & Natural Selection


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.
 Lyell agreed with him and stated that volcanoes and
earthquakes have and continue to change the earth.

Thomas Malthus (1798) – predicted the human
population would grow faster than the space and
food supplies needed to sustain them.
 Example: War, famine, disease

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!
› Tendency towards perfection- continually changing to be
successful.
 Ex: birds acquired urge to fly
› Use and Disuse- by using organ eventually change
 Ex: birds in order to fly develop wings
› Inheritance of Acquired Traits
 Ex: Lift weights build muscles and offspring will inherit big
muscles
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All of the previous peoples ideas influenced
Darwin’s thinking…

Charles Darwin (1831) – Set sail on the

Darwin’s “Theory of Evolution” would turn
the scientific world upside down!!!
H.M.S. Beagle. This voyage provided him
with much of the data and evidence that
lead to his theory of evolution
James Hutton
Charles Darwin
Jean-Baptiste Lamark
Thomas Malthus
Lamarck vs. Darwin

http://www.angelfire.com/bug/darwinvs
lamarck/
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 organism found on different islands
had varying characteristics, like appearance
and behavior, this is variation.
› Examples:
 Giant Galapagos Tortoises with varying shell shape.
 Darwin’s Finches – beak shape differed among the
birds.
A trait/characteristic that an organism is
born with
 All organisms have adaptations that help
them survive and thrive

› Structural adaptations are physical features
of an organism like the bill on a bird or the fur
on a bear.
› Behavioral adaptations are the things
organisms do to survive. For example, bird
calls and migration are behavioral
adaptations.
› Physiological adaptations are chemical
responses to stimuli to maintain homeostasis
Occurs in all populations
 Sexual reproduction increases the
chance of natural variation because of
the gene shuffling of meiosis
 Occurs far less frequently in asexual
reproduction

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1859 – Darwin published his work: On the
Origin of Species

Two main points:
1. Species were not created in their present
form, but evolved from ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
 Humans had been employing “artificial
selection” for many years!

The selective breeding of domesticated
plants and animals by man.

Question:
What’s the ancestor of the domesticated
dog?
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Answer: WOLF
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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!

Examples of adaptations that make organisms “fit”…

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.

Fossil Record
 Older fossils are in lower rock layers

Geographic Distribution of Living Species
› Species evolve differently based on
where they live.
› Due to different climate changes
adaptations resulted in differences.
› Similar areas tended to have similar
adaptations
Anatomy-body parts
 Homologous Structures

› Wing bat resembles forelimb of mammal, not
bird
› Bird wing resembles reptile forelimb
Analogous Structures
similar looking but evolutionary
unrelatred
Vestigial organsno function now but did have a function
in ancestors. Ex: appendix, tailbone
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Similarities in Early Development
› Embryos of related ancestors
are similar in early stages
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Biochemical Evidence
› Common DNA and RNA
sequences; genes
Definition: forming a new species
 What is a species?
› Group of similar organisms that can breed and
produce fertile offspring.

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Isolating Mechanism
› features of behavior , morphology, or genetics which
serve to prevent breeding between species.
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Reproductive Isolation
› mechanisms that prevent two or more populations
from exchanging genes
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Isolating Mechanism = Reproductive Isolation=
Formation of a new species

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

Geographic Isolation – When one species
becomes separated by some barrier (river,
mountain, 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).
› Example Orchids in the rainforest, only release
pollen 1 day!
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Reproductive Isolation- Can’t interbreed and have
separate gene pools
 Example  Lion and a Tiger make a Liger which
is sterile.

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.

Gene Pool = the combined genetic info
of all the members of a specific
population.

Genetic Variation is Critical to Evolution
› Mutations
› Gene shuffling as a result of sexual
reproduction
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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.
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Genetic Equilibrium: when allele frequency remains
constant in a population.

Hardy-Weinberg Principle: allele frequency remains
constant in a population (no evolution)of these
factors are present in the population.
 Random mating
 Population size very large
 No movement in or out
 No mutation
 No natural selection
Three Major Types of “Natural Selection”
 Directional Selection
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Stabilizing Selection
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Disruptive Selection
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Form of natural selection by which the entire curve
moves.

Occurs when individuals at one end of the distribution
curve have higher fitness than individuals in the middle
or at the other end of the curve.
Key
Directional Selection
Low mortality,
high fitness
High mortality,
Food becomes scarce.
low fitness

Form of natural selection by which the center of the curve
remains in its current position.

Occurs when individuals near the center of distribution curve
have higher fitness than individuals at either end.
Stabilizing Selection
Key
Low mortality,
high fitness
High mortality,
low fitness
Birth Weight
Selection
against both
extremes
keep curve
narrow and
in same
place.

Form of natural selection in which a single curve
splits into two.

Occurs when individuals at the upper and lower
ends of a distribution curve have higher fitness than
individuals near the middle.
Disruptive Selection
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two
subgroups
specializing in
different seeds.
Number of Birds
in Population
Key
Beak Size
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size

Random change in allele frequency,
based on the laws of probability.
Example  Founder Effect
› Founder Effect: change in allele frequencies
as a result of the migration of a small
subgroup of population.
 Fossil
Evidence
 Fossils provide proof of changes to life on earth
 Relative dating – estimate fossil’s age
compared to other fossils
 Radioactive dating – age of fossil based on
amount of remaining radioactive isotopes it
contains
 Geological Time

Early History
 Early atmosphere contained carbon dioxide, carbon
monoxide, nitrogen, water vapor
 Miller and Urey’s experiment show how a mixture of
early atmospheric compounds could produce simple
organic compounds found in living things
 Rise of oxygen drove some life forms to extinction but
many evolved and used oxygen for respiration and
prospered
 Endosymbiotic theory – eukaryotic cells arose from
prokaryotic cells
 Geological
Time Table
 Paleozoic – Marine life
 Devonian – animals invade land
 Mesozoic – Dinosaurs and flowering plants
 Cenozoic - Mammals
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Patterns of Evolution
 Mass extinction
 Adaptive Radiation: Single species evolves into
many species quickly
 Ex. Dinosaurs and mammals
 Convergent evolution – unrelated organisms
resemble each other
 Ex dolphin and shark
 Coevolution – 2 species evolve in response to
changes in each other
 Ex flowers and insects
 Punctuated Equilibrium – long stable periods
interrupted by brief periods of rapid change
 Changes in developmental genes- new research
shows “hox” genes are master control genes and
can control how evolution occurred.
The Miller-Urey Experiment
Miller and Urey created a
simulation of the predicted early
atmosphere of the Earth.
 When they combined the
atmospheric components with
electricity, they produced
organic compounds including
amino acids.

The Evolution of Life
Some scientists believe that RNA was the first genetic
information
 The first life forms are thought to be single-celled
prokaryotes (found from microfossils in rock) similar to
bacteria.
 Later, photosynthetic bacteria produced oxygen.
› This oxygen combined with iron in the water, forming
rust, which dropped to the ocean floor and left the
ocean blue-green
 Most organisms evolved new metabolic pathways that
would allow them to live in the new oxygen-rich
environment.
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The Evolution of Life


Eukaryotic Cells evolved from prokaryotes that
began evolving internal cell membranes.
Some small prokaryote then entered a larger
prokaryote to form a mutualistic relationship.
› These smaller prokaryotes were able to use oxygen
(aerobic respiration) and evolved into what is now our
mitochondria…recall that mitochondria have different
DNA than the rest of the cell.


This is called the Endosymbiotic Theory.
The evolution of Sexual Reproduction allowed much
more genetic variation among eukaryotes.
The Endosymbiotic Theory
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A descriptive Diagram: