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Evidence For Evolution
Darwin and His Observations
Evolution
ò  Change in a kind of organism over time
ò  The process by which modern organisms have
descended from ancient organisms
Voyage of the Beagle
Voyage began in 1831
Ñ  England – New Zealand – Australia – South
Africa – British Isles – South America –
Galapagos Islands
Ñ 
Darwin’s Observations
ò  Patterns of Diversity – Plants and animals seem suited to the
environment they live in. Ex: Argentina and Australia have
similar grassland ecosystems, but have very different animals.
Also, England has similar grasslands but no Kangaroos.
Why?
Ñ 
Living Organisms and Fossils– Some of the
fossils Darwin collected resembled
organisms that were still alive, while
others looked completely unlike anything
ever seen. How were fossil species
related to living species?
Darwin’s Observations
Ñ 
The Galapagos Islands– Although the
Galapagos Islands are close together, the
islands have very different climates.
Ó 
Ó 
Ex: Darwin observed that the giant
tortoises varied from one island to
another. The shape of a tortoise’s shell
could be used to identify which island a
particular tortoise inhabited.
Ex: Darwin noticed several types of small
birds with differently shaped beaks.
An Ancient, Changing Earth
ò  James Hutton and Charles Lyell helped scientists
recognize that Earth is many millions of years old, and
the processes that changed Earth in the past are the same
processes that operate in the present.
Lamarck’s Evolution Hypothesis
ò  Tendency Toward Perfection –
organisms are continually changing and
acquiring features that help them live
more successfully in their environments.
ò  Ex: over many generations, birds kept
trying to fly, their wings increased in
size, and they became more suited to
flying.
ò  Use and Disuse – Organisms could alter
the size or shape of particular organs by
using their bodies in new ways.
ò  Ex: If a winged animal did not use its
wings, the wings would decrease
through generations and disappear.
Lamarck’s Evolution Hypothesis
cont…
ò  Inheritance of Acquired Traits
- Acquired characteristics can
be inherited
ò  Ex: If you spend your life
lifting weights to build
muscles, your children will
inherit big muscles.
ò  Summary – Was Lamarck
correct? ______________
Inherited Variation and Artificial
Selection
ò  Heritable variation in
organisms is caused by
variations in their genes
ò  Genetic variation is found in
wild AND domesticated
species
ò  Plant and animal breeders
use genetic variation to
improve crops and livestock
(largest hogs, fastest horses,
etc)
ò  Artificial selection – nature
provides the variation and
humans select the variations
they find useful.
Evolution by Natural Selection
ò  The Struggle for Existence
ò  High birth rates and shortages of resources force
organisms into a competition for resources (food, living
space, etc).
Evolution by Natural Selection
ò  Survival of the Fittest
ò  Fitness – ability of an
individual to survive and
reproduce in its environment
ò 
Fitness is the result of
adaptations (inherited
characteristics that increase
an organism’s chance of
survival)
ò  Survival of the Fittest –
individuals better suited to
their environment survive and
reproduce
ò  Natural Selection – results in
changes in the inherited
characteristics of a
population, resulting in an
increase in fitness.
Evolution by Natural Selection
ò  Descent with Modification
ò  Species today look different from
their ancestors. Each living
species has descended, with
changes from other species over
time.
ò  This implies that all living
organisms are related to one
another
ò  Common Descent – all species
living and extinct were derived
from common ancestors. “Tree
of Life”
Evidence for Evolution
ò  The Fossil Record – By comparing fossils from older
rock layers with fossils from younger layers, scientists
could document the fact that life on Earth has changed
over time.
ò  Cephalopods have changed their shape over time in very
obvious ways
Evidence for Evolution
ò  Geographic Distribution of
Living Species – Species
that live on different
continents descended from
different ancestors but,
because some were living in
similar ecological
conditions, they were
affected by natural selection
in similar ways. Because of
this, they ended up evolving
certain features in common.
Evidence for Evolution
ò  Homologous Body Structures – Structures that have different
mature forms but develop from the same embryonic tissues
are called “homologous structures”.
ò  Vestigial organs – believed to be remnants of body parts that are
no longer seen as necessary.
Evidence for Evolution
ò  Similarities in Embryology –
Embryos of many animals with
backbones are very similar, meaning
the same groups of embryonic cells
develop in the same order and in
similar patterns to produce tissues
and organs of all vertebrates.
Darwin’s Theory of Evolution
ò  Individual organisms differ, and some of this variation is
heritable
ò  Organisms produce more offspring than can survive, and
many that do survive do not reproduce
ò  Because more organisms are produced than can survive, they
compete for limited resources
ò  Individuals best suited for their environment survive,
reproduce, and pass heritable traits to their offspring. This
causes species to change over time
ò  Species alive today are descended with modification from
ancestral species, forming a “tree of life”