Download Theory of Evolution

Darwin's Theory of
Evolution
Unlocking Darwin’s Mysterious Idea
Darwin’s Voyage of Discovery
Darwin’s Epic Journey
He was born February 12th 1809
This year we celebrate his 203rd birthday!!
Darwin developed the biological theory of
evolution that explains how modern
organisms evolved over long periods of
time through descent from common
ancestors
In 1831, he began a 5 year voyage on the
HMS Beagle that would change his life.
Observations Aboard the Beagle
Species Vary Globally
Different, but similar,
animals inhabited
separate, but similar,
habitats
That some similar
environments have very
different animals.
(Kangaroos in Australia
but not England)
Species Vary Locally
Different, yet related, animals
occupied different habitats within a
local area
Exs. – Tortoises and Birds in the
Galapagos Islands varied from island
to island
Species Vary Over Time
Some fossils of extinct animals
were similar to living species
Ex. – Extinct giant armored
Glyptodont is similar to and lived
in the same area as the Armadillo
Giant Ground Sloth
Modern Sloth
Putting the Pieces of the
Puzzle Together
Darwin thought about the patterns he’d seen
on his voyage
He realized that there were many similarities
between the animals he’d seen
There was evidence that suggested that
species were not fixed and that they could
change by some natural process
Ideas That Shaped Darwin's
Thinking
An Ancient, Changing Earth
The Earth is very ancient and is
continuously changing.
– Hutton and Lyell helped scientists see that the
Earth is millions of years old.
– The geologic processes that shaped the Earth
happen very slowly and are still happening
today.
Hutton and Geological Change
Hutton proposed that rocks form very
slowly and are changed by forces that
twist, lift and fold them
He also realized that mountains can be
worn down by rain, wind, heat and cold
In order for these events to occur, he
concluded that the Earth must be more
than a few thousand years old
Lyell’s Principles of Geology
Believed that the geological processes we see
today must be the same ones that shaped Earth
millions of years ago
There needed to be enough time in Earth’s history
for these changes (like a river carving out a
canyon) to take place
He agreed with Hutton that the earth was much
older than a thousand years
Cuvier was an anatomist who studied
fossils.
Noticed that some fossils indicate that
organisms in the past were very different
from living organisms of today.
Older fossils differed more from living
species than younger fossils.
Abrupt changes in the fossil record shows
evidence of mass extinctions.
Darwin’s Observations
While in South America, Darwin witnessed
an earthquake that was strong enough to lift
the rocky shoreline 3 meters out of the sea –
with mussels and other sea life clinging to it
Later, he observed fossils of marine animals
in mountains thousands of feet above sea
level
Lamarck’s Evolutionary
Hypotheses
Proposed that the use or disuse of organs
caused organisms to gain or lose traits over
time.
These new characteristics could be passed
on to the next generation.
Ex. - A water bird’s long legs happen
because the animal kept wading in deeper
water to get food.
Evaluating Lamarck’s Hypotheses
Lamarck’s hypotheses were incorrect in
many ways
We know that traits acquired during a
lifetime cannot be passed on to offspring
Evaluating Lamarck’s Hypotheses
However, Lamarck was one of the first to:
– Suggest that species are not fixed
– Explain that evolution uses natural processes
– Recognize that there is a link between an
organism’s environment and its body structures
Lamarck’s work paved the way for later
biologists, including Darwin
Darwin’s Ideas
Descent with Modification
– Every species-living and extinct- must have
descended by reproduction from preexisting
species and that species must be able to change
over time.
Natural Selection
– The mechanism for descent with modification
Darwin’s Reasoning
Overproduction
– More offspring can be produced than can
survive to maturity.
– The environment limits the populations of all
organisms by causing deaths or by limiting
births
– Based concept on the ideas of Malthus who
speculated that human populations are limited
by war, famine and disease.
Genetic variation: individuals have different
traits in any population and some of these
traits are inherited.
Struggle to Survive: individuals compete
with each other. Some variations improve
an individual’s chance to survive and
reproduce. These favorable variations are
called adaptations.
Differential Reproduction
– Organisms with the best adaptations survive
and reproduce. Those without die.
– Over time, favorable adaptations increase in the
population.
– Nature changes species by selecting traits
(parents) that are passed on to the next
generation.
Artificial Selection
In artificial selection, nature provides the
variations, and humans select the ones they
find useful
Darwin knew that variation occurs in wild
species as well as domesticated species
He realized that that natural variation
provided the raw material for evolution
Artificial Selection
Darwin Presents His Case
Darwin wanted to gather as much evidence as he
could to support his ideas before he made them
public
In 1858, Darwin read an essay by Alfred Wallace
whose thoughts about evolution were almost
identical to his!
In order to not get “scooped”, Darwin decided to
present his work at a scientific meeting in 1858
along with some of Wallace’s essay
The next year, Darwin published his complete
work on evolution: On the Origin of Species
Evolution by Natural Selection
Struggle for Existence
– From Malthus’ theory of supply and demand,
Darwin reasoned that if more individuals are
produced than can survive, they will have to
compete for food, living space and other
necessities of life
– Darwin described this as the struggle for
existence
Evolution by Natural Selection
Variation and Adaptation
– Individuals have natural variations among their
inheritable traits
– Some variations are better suited to life in their
environment than others
– Fast predators capture prey more efficiently
– Prey that are faster, better camouflaged or
better protected avoid being caught.
Variation and Adaptation
– Any heritable characteristic that increases an
organisms ability to survive and reproduce in
its environment is called an adaptation
– Examples of Adaptations:
•
•
•
•
Tiger’s claws
Camouflage colors
Plant structures
Avoidance behaviors
Adaptations
Survival of the Fittest
Darwin felt that there must be a connection
between an animal’s environment and how
it survives
Ability to survive and reproduce in a
specific environment is called FITNESS
Fitness depends upon how well an organism
is suited for its environment
Fitness is a result of ADAPTATION
Good adaptations allow organisms to
survive and are passed on to their offspring.
Good fitness: Reproduce
Low Fitness: Few offspring/extinction
Darwin thought that this seemed very
similar to artificial selection
He referred to “survival of the fittest” as
Natural Selection
Survival means more than just staying alive.
It means reproducing and passing
adaptations on to the next generation
Natural Selection: Nature chooses
Artificial selection: Man chooses
Favorable characteristics are inherited over
several generations.
Artificial Selection
(Breeding Livestock)
Natural Selection
(Bird of Paradise Mating Display)
Natural Selection
Natural Selection
Natural Selection is the process by which
organisms with variations most suited to
their local environment survive and leave
more offspring
Natural Selection occurs in any situation in
which more individuals are born than can
survive
Over time, natural selection results in
changes in the inherited characteristics of
a population.
These changes increase a species’ fitness
in its environment.
Common Descent
Natural selection produces organisms with
different structures than their ancestor,
different niches, and new habitats.
Each living species has descended, with
changes, over time.
The Evolution of the Horse
If we look back far enough we could find
the common ancestors of all living things.
A single “tree of life” links all living things
This is known as the principle of common
descent.
Evidence of Evolution
Darwin argued that living things have been
evolving on Earth for millions of years.
Today, fields like genetics and molecular
biology support Darwin’s basic ideas about
evolution
Biogeography
Darwin recognized the importance of pattern in
the distribution of life
Biogeography is the study of where organisms
live now and where they and their ancestors lived
in the past
Two biogeographical patterns are significant to
Darwin’s theory:
Closely Related but Different
This is a pattern in which closely related species
are different in slightly different climates
To Darwin, the biogeography of the Galapagos
species suggested that populations on the island
had evolved from mainland species
Over time, natural selection on the islands
produced variations among populations that
resulted in different, but closely related, island
species
Darwin noticed that all the birds he had collected
throughout the Galapagos were all finches
Lines of Evidence: Geography
Distantly Related but Similar
This is a pattern in which very distantly related
species develop similarities in similar
environments
Darwin noted that similar ground-dwelling birds
inhabit similar grasslands in Europe, Australia
and Africa.
Differences in body structures indicate that they
evolved from different ancestors, but similarities
provide evidence that similar selection pressure
caused species to develop similar adaptations
Geographic Distribution
of Living Species
The Age of Earth and Fossils
The Age of Earth
Darwin viewed the fossil record
as core evidence of evolution
He proposed that Earth was
hundreds of millions of years
old, instead of a few thousand
He argued that countless species of many
different forms had appeared on Earth, lived
for a long time and then vanished
From viewing the remains found in rock
layers, it was observed that species indeed
changed over time.
Lines of Evidence: Transitional Forms, Page 1 of 2
The Age of Earth and Fossils
The Age of Earth
– Half a century after Darwin published his
theory, scientists discovered radioactivity
– Scientists now use radioactivity to establish the
age of rocks and fossils
– Radioactive dating indicates that the earth is
about 4.5 billion years old, which supports
Darwin’s idea that the Earth was very old
The Age of Earth and Fossils
Recent Fossil Finds
– During Darwin’s time, not enough intermediate fossils
had been found to document the evolution of modern
species from their ancestors
– Since Darwin, paleontologists have discovered
hundreds of fossils that identify intermediate stages in
the evolution of many different groups of modern
species
– Exs:
• Whales
• Dinosaurs
Birds
• Fish
Four-Legged Animals
Comparing Anatomy and Embryology
In Darwin’s time, scientists noted that all
vertebrate limbs had the same basic bone structure
But some were used for crawling, some for
climbing, some for running and others for flying
Homologous Structures
Same Structure, Different Function
What does it show? Evidence of a common ancestor
Homologous Structures
Darwin proposed that animals with similar
structures evolved from a common ancestor with a
basic version of that structure
Similarities and differences among homologous
structures help determine how recently species
shared a common ancestor
Homologous structures have also been found in
plants
Analogous Structures
The clue to common descent is common structure,
not common function
NOT inherited from a common ancestor.
Analogous Structures
– Body parts that share a common function , but not
structure
– Same function, Different structure
Exs. – The wing of a bee and the wing of a bird
Analogous Structures
Vestigial Structures
Vestigial structures are those structures that
are similar but are reduced in size and
remain unused
Humans have a vestigial structure. Can you
name it?
Vestigial pelvis and femur in a modern whale.
Vestigial
Structures
Embryology
Embryology is the study of the early stages
of development of an organism
Researchers noticed a long time ago that
vertebrate embryos look very similar
The same groups of embryonic cells
develop in the same order and in similar
patterns
Embryology
Vertebrate embryos have fold of tissue in
the neck region called gill pouches
In fish these develop into gills
In human these same pouches develop to
form inner ear bones.
Embryology
Lines of Evidence: Molecular Evidence
Similarities in early development suggest a common ancestor
Genetics and Molecular Biology
Biochemists study and compare chemicals
found in living things (DNA and Proteins)
The genetic code is nearly identical in
almost all organisms
This is powerful evidence that all organisms
evolved from common ancestors that shared
this code
DNA
Sequencing