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Evolution
Evolution

Process by which modern organisms have
descended from ancient organisms
Voyage of the Beagle
Charles Darwin set sail around the world
 While on his journey, he made many
observations and collected evidence that
led him to propose a hypothesis about
the way life changes over time
 His ideas are now a theory

Voyage of the Beagle
Darwin collected specimen of plants and
animals
 He observed that plants and animals were
well adapted to the environment they
were in
 He was puzzled by where different
species did and did not live

Voyage of the Beagle
Also on his journey, Darwin picked up
fossils he found
 At one point on his trip, he visited the
Galapagos Islands which is west of South
America
 All the islands there had different climates
and the turtles there differed by their
shells

Section 15-1
Giant Tortoises of the
Galápagos Islands
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Dome-shaped shell
Hood
Saddle-backed shell
Voyage of the Beagle



Darwin also found tons of birds on the
islands that varied in their beaks
Overall he found that the characteristics of
many plants and animals varied among the
different islands
He wondered if the species on the different
islands had once been members of the same
species from an original South American
ancestor species
Ideas Behind Darwin’s Thinking
In Darwin’s day, people believed that
forms of life had been created only a few
thousand years ago.
 They also believed that the planet and
living things had not changed at all over
time.
 A fossil record began changing people’s
minds!

Ideas Behind Darwin’s Thinking
Scientists helped to show that Earth is
many millions of years old and the
processes that changed earth in the years
past are the same processes that operate
in the present.
 Hutton (1785) – says that the earth is
shaped by geological forces that took
place over very long periods of time. The
earth is millions of years old!

Movement of Earth’s Crust
Section 15-2
Sea
level
Sea
level
Sedimentary
rocks form in
horizontal layers.
When part of Earth’s
crust is compressed,
a bend in a rock
forms, tilting the rock
layers.
As the surface
erodes due to water,
wind, waves, or
glaciers, the older
rock surface is
exposed.
New sediment is
then deposited
above the exposed
older rock surface.
Ideas Behind Darwin’s Thinking
Malthus (1798) – he reasoned that if the human
population continued to grow unchecked,
sooner or later, there would be insufficient
living space and food for everyone
 Lamarck –
◦ He said that living things have changed over
time and that all species were descended
from other species
◦ He also realized the organisms have adapted
to their environment

Ideas Behind Darwin’s Thinking
◦
Lamarck’s ideas were being shared in 1809 (the year
Darwin was born)
1. Tendency toward perfection – all organisms have a
tendency to strive complexity and perfection
 Organisms are constantly changing and acquiring
new features to make them more successful
2. Use and disuse of organs –
 Organisms acquired or lost certain traits during
their lifetime
 These new traits could be passed on to their
offspring
This process led to changes in species
Section 15-2
Figure 15–7 Lamarck’s Theory
of Evolution
Ideas Behind Darwin’s Thinking
The only thing Lamarck was really right
about was that organisms are adapted to
their environment.
 Lyell (1833) – “Principles of Geology” –
the processes occurring now have shaped
earth’s geological features over long
periods of time.

Darwin’s Origin of Species
The birds found on Galapagos Islands
belonged to three different species found
no where else in the world
 He found that all the islands species were
different from the mainland species
 Darwin only published his work after he
saw that Wallace’s ideas were similar to
his.

Darwin’s Origin of Species
In his work, he described the ideas behind
natural selection
 He said that variation mattered
 In artificial selection, nature provided the
variation and humans selected those
variations that they found useful
 At this time, no one knew about genetics!

Natural Selection
The struggle for existence
 Members of each species compete
regularly to obtain food, living space and
other necessities of life (predator versus
prey)
 Everything centered on the idea of
Survival of the Fittest

Natural Selection

Survival of the Fittest
◦ All depends on how well suited an organism is to
its environment
◦ Fitness – the ability of an individual to survive and
reproduce in its environment
◦ Adaptations - any inherited characteristic that
increases an organism’s chance of survival
◦ A successful adaptation enables organisms to
become better suited to their environment and
better suited to survive and reproduce
Natural Selection

Survival of the Fittest cont’d
◦ Survival of the fittest – individuals that are better
suited to their environment survive and
reproduce most successfully
◦ Natural selection allows for survival of the fittest
because only certain individuals in a population
produce new individuals
◦ Over time, natural selection results in changes in
the inherited characteristics of a population.
◦ These changes increase a species' fitness in its
environment
Natural Selection
 Descent
with modification
◦ Each living species has descended
with changes from other species
over time
◦ All living organisms are related to
one another (a common decsent)
Concept Map
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Evidence of Evolution
Darwin said living things have been
evolving on Earth for millions of years
 Evidence –
1. Fossil record

◦
◦
◦
Fossils – the record of the history of life
Compare fossils from older rock layers to
those in younger rock layers
Also found in transitional fossils
Evidence of Evolution
2. Geographic Distribution of Living Species
◦ Species living on different continents had each
descended from different ancestors
◦ Since some animals on each continent were
living under similar ecological conditions, they
were exposed to similar pressures of natural
selection
◦ So different animals end up evolving features
in common
Figure 15–14 Geographic
Distribution of Living Species
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
Evidence of Evolution
3. Homologous Body Structure
◦
◦
◦
◦
He found anatomical similarities among the
body parts of animals with backbones
Ex – arms, wings, legs and flippers
All differ from the function they perform but
they are all from the same basic bones
Limbs have adapted in ways for organisms to
survive
Figure 15–
15 Homologous Body
Structures
Turtle
Alligator
Ancient lobe-finned fish
Bird
Mammal
Evidence of Evolution
◦ Homologous structure – structures that have
different mature forms but develop from the
same embryonic tissues
 This is evidence that all 4-limbed vertebrates have
descended from common ancestors
◦ Vestigial organs – homologous structures that
serve no important function
 They are not eliminated by natural selection
because they don’t affect an organism’s ability to
survive and reproduce
Evidence of Evolution
4. Similarities in embryology
◦ Embryonic stages are similar
◦ They look similar in early stages of
development
◦ There are common cells and tissues that grow
in similar ways
Anatomy and Embryology
Anatomy and Embryology
Anatomy and Embryology
Anatomy and Embryology
Summary of Darwin’s Theory
1.
2.
3.
Individual organisms differ and some of
this variation is heritable (can be passed
on).
Organisms produce more offspring that
can survive and many that do survive do
not reproduce
Organisms compete for limited
resources
Summary of Darwin’s Theory
4. Each unique organism has different
advantages and disadvantages in the
struggle for existence.
◦ Individuals best suited reproduce most
successfully.
◦ They pass on their heritable traits.
◦ Others die or leave less offspring.
◦ SO species will change over time.
Summary of Darwin’s Theory
5. Species alive today are modifications
from ancestral species that lived in the
past.
◦ ALL ORGANISMS ARE UNITED!!!!