Download Chapter 15 Darwin*s Theory of Evolution

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• All
living things share a
common ancestor.
• We can draw a Tree of Life to
show how every species is
• Evolution is the process by
which one species gives rise to
another and the Tree of Life
• The theory of Evolution
deals with how evolution
happens. Our
understanding of this
process is always changing.
• Evolution is also a fact as
there is a huge amount of
indisputable evidence for its
Most scientists in Darwin’s day thought the
Earth was only a couple thousand years old
 They believe that Earth had not changed, nor had
any of its species
These two men helped
scientists recognize that Earth
is many millions of years old
and the processes that
changed Earth in the past are
the same ones operating now
– father of modern
geology; hypothesis regarding
geological forces that have
shaped Earth
– echoed Hutton; past
events that affected the earth
are still happening
One of the first scientists to
recognize that living things
have changed over time
Species were descended from
other species
Also realized that organisms
had adapted to their
 By selective use or disuse of
organs, organisms acquired or
lost certain traits during their
The idea that organism’s alter
their body by using it in new
All organisms have an innate tendency
toward complexity and perfection
Organisms will continually change and
acquire features that bring them closer to this
Believe acquired traits could be inherited
If an organism’s body was altered, it would
pass that trait to its offspring
1809 - 1882
Most influential
contributor to thoughts
about evolution
Wrote The Origin of
 1859 – published
Presented evidence for
changes in species through
Natural Selection
 Traveled around the world;
notable work in the
Galapagos Islands
5 year round-the-world voyage
 1831 - at age 22
 H.M.S. Beagle
 Ship’s naturalist
 At beginning of trip - believed
species were immutable
 Collected and examined the
species that inhabited the
regions the ship visited
 Fossils, coral ,plants, animals
Volcanic islands - 3.5 mya
Isolated, west of Ecuador
All inhabitants are descended
from species that arrived on
islands from elsewhere
Blue-footed Booby
13 species of finches
Share many
morphological features
 Differ in several ways
 Beak size
 Beak shape
 Food eaten
Evolved from a single
 He attempted to correlate
variations in their traits
with environmental
Short neck
Domed shell
Long neck
Flared shell
Marine Iguana
Algae eater
Land Iguana
Terrestrial vegetation
 The characteristics of many
animals and plants varied
noticeably among the
different islands of the
Groups of 3-4
4 trials
Start each new
generation with
100 butterflies
Be careful with
the butterflies!
Natural selection results in changes in the
inherited characteristics of a population.
These changes increase a species’ fitness (ability to
survive and reproduce) in its environment
Darwin’s Evolutionary Ways of Thinking
Darwin publishes Origin Of Species in 1859
Prompted after Wallace publishes essay
Words/phrases we are introduced to
 Artificial selection
 Struggle for existence
 Fitness
 Adaptation
 Survival of the fittest
Nature provides variation, humans select
variation that they found useful
 Livestock
Members of the same species compete
 What are they competing for?
What Darwin called the ability of an individual
to survive and reproduce
Fitness is a result of adaptation
Adaptation  any inherited characteristic
that increases an organism’s chance of
Individuals with
characteristics that are
better suited to their
environment –
adaptations that enable
their fitness – survive and
reproduce most
 Over time, natural selection
results in changes in the
inherited characteristics of a
 These changes increase a
species’ fitness in its
Principle proposed by Darwin
Over long periods of time, natural selection
produces organisms that have different
structures, establish different niches, or
occupy different habitats
RESULT  species today look different
from their ancestors
All species, living and extinct, are derived
from a common ancestor
A single “tree of life” links all living things!
Darwin argued living things have been
evolving on Earth for millions of years
 Evidence for this process can be found:
▪ Fossil record
▪ Geographical distribution of living species
▪ Homologous structures of living organisms
▪ Similarities in embryology
Fossils  remains of ancient life
Darwin compared fossils from older rock
layers to those in younger rock layers to
document the change of life on Earth
© World Health Org.
complex cells
The fossil record shows a sequence from simple bacteria to more
complicated organisms through time and provides the most
compelling evidence for evolution.
Species living on different geographical areas had each
descended from different ancestors
 However, because of similar ecological conditions they
were exposed to similar pressures of natural selection 
similar features
Structures that have
different mature
forms in different
organisms, but
develop from the
same embryonic
Organs of many species are so reduced in size
that they are just traces of homologous
organs in other species
Examples: miniature legs, tails
Wisdom Teeth
Particular Ear Muscles
Plica semilunaris
Embryology of many animals with backbones are
very similar
 Certain embryonic cells develop in the same order and in
similar patterns to produce the tissues and organs of all
At one point… you
looked like this.
Thought you should
 Individuals organisms differ, and some of this
variation is heritable
 Organisms compete for resources
 Each organism has different
advantages/disadvantages  organisms best
suited survive and pass their traits to offspring
 Species today are descended with modification
from ancestral species; common ancestor, single
tree of life