Download Darwin`s Theory of Evolution

Darwin’s Theory of
Evolution
Chapter 16
Voyage of the Beagle
1831 – set sail around the world
 Collected plant and animal specimens
 Explained how modern organisms evolved
over long periods of time through descent
from common ancestors

3 Distinct Patterns of Biodiversity
Species vary Globally
 Species vary locally
 Species vary over time

Species Vary Globally

Different, yet ecologically similar, animal
species inhabited separated, but
ecologically similar, habitats around the
globe
Rhea
Ostrich
Emu
Patterns of Diversity

Visited Argentina and Australia
– Very similar ecosystems = both grasslands
– Yet very different organisms at each
– Why no rabbits in Australia and no kangaroos
in Argentina?
Species Vary Locally

Different, yet related, animal species often
occupied different habitats within a local
area
The Galapagos Islands
Islands very close together but very
different climates
 Darwin studied land tortoises and marine
iguanas
 The shape of a tortoise’s shell could be
used to identify which island it came from

Giant Tortoises of the Galápagos
Islands
Section 15-1
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
Darwin’s Finches
Back in England
Darwin observed the characteristics of
many animals and plants varied noticeably
among the different islands of the
Galapagos
 Hypothesis – These separate species
evolved from a South American ancestor
after being isolated from one another

Species Vary Over Time
Some fossils of extinct animals were
similar to living species
 Some fossils looked like nothing alive
today
 Why had so many of these species
disappeared?
 How were they related to living species?

Contributing to Darwin

James Hutton
– Looked at geological forces and rock
formations
– Earth was shaped by geological processes
that work very slowly…millions of years
Earth had to be millions of years old
Charles Lyell

Principles of Geology
Uniformitarianism – Laws of nature are
constant over time
 Darwin witnessed these events

– Volcanoes
– Earthquakes

Lyell explained how these events formed
the Earth
If Earth could
change over time,
could life change
too?
Lamarck’s Theory of Evolution

Organisms acquired traits from use and
disuse and then passed these traits on
– Organisms had a tendency for perfection
– Use and Disuse
– Inheritance of Acquired Traits
Lamarck’s Theory
Thomas Malthus
Realized that babies being born faster
than people dying
 Hypothesized – If the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space and food for everyone
 Darwin applied this to other organisms

Darwin’s Case
Didn’t want to publish findings
 Alfred Russel Wallace, naturalist,
published an essay on evolutionary
change


On the Origin of Species
Natural Variation and Artificial
Selection
Every species exhibits some variation –
Natural Variation
 Darwin noted that farmers used selective
breeding
 Artificial selection – nature provides the
variation and humans selected those
variations for offspring

Evolution by Natural Selection

Struggle for Existence
– Malthus
– Organisms competing for resources
Evolution by Natural Selection

Variation and Adaptation
– Individuals have natural variations
– Some better suited to life in their
environments than others
– Adaptation – any heritable characteristic
that increases an organism’s ability to survive
and reproduce in its environment
Bactrian
camel
Camels have many
adaptations that allow
them to live successfully
in desert conditions.
Sea Otters
Sea otters spend almost their entire lives in water. They eat,
sleep, and even have their babies in water. How is their fur
adapted to keep them warm? Why is it a critical situation when
otters encounter oil spills?
Platypus
How are platypuses
adapted for the time
they spend in water?
Katydids
Butterflies and Mimicry
One butterfly is a Monarch and one is a Viceroy.
Can you tell the difference? Why might
butterflies adapt to look the same?
Insect Eating Pitcher Plant
Palo verde tree bark
What adaptation does this plant have?
Hint: It has to do with the bark.
Evolution by Natural Selection

Survival of the Fittest
– Each individual exhibits fitness which is a
result of adaptation
– Fitness = how well an organism can survive
and reproduce in an environment

Survival of the Fittest – difference in rates
of survival and reproduction
Natural Selection

Natural selection – only certain individuals
are “selected” to reproduce
– Environment Chooses!

Occurs when…
– Struggle for existance
– Variation and adaptation
– Survival of the fittest
Natural Selection results in changes in the
inherited characteristics of a population,
which increases a species’ fitness
Natural Selection
Descent with Modification
Over time, organisms fit into different
niches and have descended with
changes…
Descent with Modifications
 Implies that everything is related to each
other…
Common Descent
Darwin concluded that you could make
one large tree of life for all living things

Evidence
of
Evolution
Fossil Record
Geographic
Distribution
of Living Species
Homologous
Body
Structures
Similarities in
Early
Development
Physical remains
of
organisms
Common
ancestral
species
Similar Genes
Similar Genes
Fossils

Many recently discovered fossils form
series that trace the evolution of modern
species from extinct ancestors
Geographic Distribution of
Living Things

Biogeography
– where organisms live now and where they and their
ancestors lived in the past
Closely related species differentiate in slightly
different climates (ex. Galapagos)
 Distantly related species develop similarities in
similar environments (ex. Flightless birds)

– Same ecological pressures → similar pressures of
natural selection → Evolved common traits
Homologous Body Structures
Turtle
Alligator
Bird
Mammals
Typical primitive fish

Homologous structures have developed from the
same embryonic tissues but have different
mature forms
– Descended, with modification, from common
ancestors
Homologous Body Structures
Homologous Body Structures
Homologous Body Structures – different
function yet similar structure
 Analogous Body Structures – same
function yet different structure

– Ex. Bee’s wing and bird’s wing

Vestigial Structures – little or no function
Similarities in Early Development

The same groups
of embryonic
cells develop in
the same order
and in similar
patterns to
produce tissues
and organs of all
vertebrates,
producing
homologous
structures
Genetics and Molecular Biology
DNA and homologous molecules provide
evidence of common descent
 Genetic code almost identical in all living
things

Testing Natural Selection
Darwin’s hypothesis
 Peter and Rosemary Grant

– Beak size and shape must have enough
heritable variation
– Beak size and shape must produce differences
in fitness
Tested on medium sized ground finch
 Grants documented data that natural
selection takes place in wild finch
populations frequently, and sometimes
rapidly

Grant’s Research
Recap of Darwin
•Evolution happens slowly over a
length of time.
•All organisms differ and some of this
variation is inherited.
•Organisms compete for resources.
•Survival of the Fittest
•Over time, natural selection causes
changes in species.
•Species have descended with
modification.
•All organisms are connected into a
tree of life by common descent.