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Evolution
What is evolution?
 Evolution is the
process of biological
change by which
species of organisms
change over time.
 Evolution is a central
theme in all fields of
biology today.
Evolution is when organisms change
over time. So, modern organisms
descended from ancient ones.
Evolution is a Theory –
Just like Gravity!
• Evolution is a well
supported
explanation of
phenomena that
have occurred in
the natural world
• A theory in science
is a well tested
hypothesis, not just
a guess
Evolutionary Scientists
 Charles Bonnet mid-1700s
 First to use term evolution
 Studied fossils
 James Hutton
 1795 Theory of Geological change
 Jean-Baptiste Lamarck 1809
 Charles Lyell
 Geographical features can be built up or torn down
 Charles Darwin
 Thomas Malthus
 Russell Wallace
 Gave Darwin the drive to publish his findings
Malthus
 Reasoned that if the
human population
continued to grow
unchecked, sooner or
later there would be
insufficient living space
and food for everyone
Jean-Baptiste Lamarck
 He proposed the idea of inheritance of
acquired characteristics:
 changes in an environment caused an
organism’s behavior to change
 this would lead to greater use or disuse of a
structure or organ.
 the structure would become larger or smaller
and would then be passed down to offspring
 For example: giraffes’ long necks
 Idea was WRONG!!
Charles Darwin
 Natural selection was
the theory he proposed
to explain evolution.
 He attempted to provide
reasons for the biological
diversity on Earth.
 Developed his theory
from personal
observations and
research of other
scientists.
Charles Darwin (1809-1882)
Sailed around the world 1831-1836
on the British ship H.M.S. Beagle.
What did
Darwin’s
Travels reveal?
 The diversity of living
species was far greater
than anyone had
previously known!!
 These observations led
him to develop the
theory of evolution!!
What did Darwin do?
 He observed the land and its inhabitants.
 Finches and Tortoises
 He noticed the physical differences among
island species.
 Species on one island looked different from
those on another island.
 Island species looked different from those
found on the mainland. This is known as
variation.
 He noticed that the physical differences among
the species were appropriate for their
environment and diet.
Finches
 Finches that live in
the area with hard
shelled nuts had
stronger beaks.
 Finches with
delicate beaks were
found where
insects and fruits
were available.
Galapagos Tortoises
 Darwin observed the saddle-back and the
domed tortoises.
 Saddle back tortoises have long
necks and legs and live in areas with
tall plants.
 Domed tortoises have shorter
necks and legs and live in wet
areas rich in mosses and shorter
plants.
Darwin finally
published his
ideas in 1859.
 Other naturalists
were developing
the same theory
that Darwin did.
 Even though he
was afraid of the
Church’s reaction
to his book he
wanted to get
credit for his work.
Natural Selection
 The traits that
help an organism
survive in a
particular
environment are
“selected” in
natural selection
Natural Selection
• Mechanism by which individuals that
have inherited beneficial adaptations
produce more offspring on average than
do other individuals.
– Survival of the fittest.
Natural Selection
• Characteristics are passed down to
offspring only if they are beneficial to
individual.
– More successful individuals are
“naturally selected” to live longer and to
produce more offspring that share the
beneficial characteristics.
• Natural selection acts only on existing
traits.
Natural Selection
 Four main principles:
1. Variation of physical traits.
2. Competition for limited natural resources.
3. Organisms produce more offspring than can
survive.

Predation, diseases
4. Individuals with beneficial traits will survive and
reproduce.

Beneficial traits are passed to offspring.
Artificial Selection
 nature provides variation, humans select
variations that are useful.
 Example - a farmer breeds only his best
livestock
Descent with Modification
 Each living
species has
descended
with changes
from other
species over
time
Evidence of Evolution
1. Fossil Record
2. Homologous Body structures
3. Similarities in Embryology
4. Biochemical Evidence
Evidence of Evolution:
The Fossil Record

Fossil record
provides evidence
that living things
have evolved

Fossils show the
history of life on
earth and how
different groups of
organisms have
changed over time
Relative
vs.
Absolute
Dating
Relative Dating
 Can determine a
fossil’s relative age
 Performed by
estimating fossil age
compared with that of
other fossils
 Drawbacks – provides
no info about age in
years
Absolute Dating
 Can determine the
absolute age in
numbers
 Is performed by
radioactive dating –
based on the amount
of remaining
radioactive isotopes
remain
 Drawbacks - part of the
fossil is destroyed
during the test
• Radiometric dating uses decay of unstable
isotopes.
– Isotopes are atoms of an element that differ in their
number of neutrons.
– A half-life is the amount of time it takes for half of the
isotope to decay.
Primate Fossils
Australopithecus
Homo erectus
Homo sapien
Primate Bone Structure
Evidence of Evolution:
Homologous Body Structures

Turtle
Structures that
have different
mature forms but
develop from the
same embryonic
tissues
Ex: Wing of bat,
human arm, leg
of turtle
Alligator
Bird
Evidence of Evolution:
Homologous Structures
 Features that are similar in structure but
appear in different organisms and have
different functions.
 Strong evidence for common ancestor.
 Ex: forelimbs of humans, bats and moles.
Human hand
Mole foot
Bat wing
Analogous Structures
 Structures that perform a similar
function.
• Not evidence of common
ancestry.
Vestigial Structures
 Remnants of organs or structures that
had a function in an early ancestor.
 Ex: Ostrich wings, used for balance but
not flight
 Ex: Humans’ appendix
Evidence of Evolution:
Similarities in Embryology
In their early stages
of development,
chickens, turtles and
rats look similar,
providing evidence
that they shared a
common ancestry.
Embryological Development
Evidence of Evolution:
Biochemical Similarities
 Scientists study nucleotide sequences in
DNA and proteins in different organisms
to determine ancestry.
 If the organisms are closely related they
will have similar sequences of
nucleotides in their DNA and
arrangement of amino acids in proteins.
Evidence of Evolution:
Biochemical Similarities
Organism
Amino Acid
Differences
Organism
Amino Acid
Differences
Human beta
chain
0
Mouse
27
Gorilla
1
Kangaroo
38
Rhesus monkey
8
Chicken
45
Dog
15
Frog
67
Cow
25
Soy bean
124
The more similar the
Adaptation
 Darwin’ observations led him to realize
that species must somehow be able to
adapt to their surroundings.
 Adaptations allow species to better survive
in their surroundings.
 Adaptations can lead to genetic change in
a population over time.
VariationSpeciation
 Individuals with beneficial trait are well suited for
the environment
 They reproduce and pass the beneficial trait to their
offspring
 Individuals without the beneficial trait are less
likely to survive and reproduce
 Their traits are not passed.
 Beneficial traits are passed while other traits
disappear
 These changes can eventually cause speciation
Rates of Evolution
 Two main views:
 Gradualism
 Evolution occurs slowly and constantly over a long
period of time
 Darwin
 Punctuated Equilibrium
 Evolution occurs in spurts
 Period of rapid speciation then long period of little to
no change
 Caused by random mutations or sudden changes in
environment
 Cambrian explosion