Transcript Chapter 14 Darwin

Darwin & Evolution
by
Natural Selection
Cactus
eater
Insect eaters
Seed eaters
Bud eater
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2006-2007
Charles Darwin
 Proposed a way how
evolution works
How did creatures
change over time?
 by natural selection

 Collected a lot of
evidence to support
his ideas
1809-1882
 British naturalist

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Voyage of the HMS Beagle
 Invited to travel around the world
1831-1836 (22 years old!)
 makes many observations of nature

 main mission of the Beagle was to chart
South American coastline
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Voyage of the HMS Beagle
 Stopped in Galapagos Islands

500 miles off coast of Ecuador
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Galapagos
Most of animals on the
Galápagos live nowhere else
in world, but they look like
species living on South
American mainland.
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Darwin found…many unique species
Many of Darwin’s observations made
him wonder… Why?
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Darwin found…clues in the fossils
Darwin found:
Evidence that creatures
have changed over time
present day Armadillos
ancient Armadillo
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Darwin found:
Different shells on tortoises on different islands
Darwin asked:
Is there a relationship
between the environment
& what an animal
looks like?
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Darwin found… birds
Darwin found:
Many different birds
on the Galapagos
Islands.
He thought he found
very different kinds…
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But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
species of finch on the
mainland!
Darwin asked:
If the Galapagos
finches came from the
mainland, why are they
so different now?
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The finches cinched it!
Darwin found:
The differences
between species of
finches were
associated with the
different food they
ate.
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different beaks are
inherited variations
said:
serveDarwin
as adaptations
that help
birds compete
Ahaaaa!
for food
A flock of South
these
birds survive
American
finches&
reproduce
were stranded on the
pass Galapagos…
on the genes for
those more fit beaks
over time nature selected
for different species with
different beaks
Relationship between species (beaks) & food
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Darwin’s finches
 Darwin’s conclusions

variations in beaks
 differences in beaks in the original flock
 adaptations to foods available on islands

natural selection for most fit
 over many generations, the finches were
selected for specific beaks & behaviors

offspring inherit successful traits
 accumulation of winning traits:
both beaks & behaviors
separate into different species

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From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small
insectivorous
tree finch
Large
insectivorous
tree finch
Small
ground
finch
Cactus
eater
Insect eaters
Seed eaters
Vegetarian
tree finch
variation
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Bud eater
Medium
ground
finch
Large
ground
finch
natural selection for best
survival & reproduction
Earlier ideas on Evolution
 LaMarck

evolution by acquired
traits
 creatures developed traits
during their lifetime
 give those traits to their
offspring

example
 in reaching higher
leaves giraffes stretch their
necks & give the acquired
longer neck to offspring

not accepted as valid
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Darwin’s view of Evolution
 Darwin
giraffes that already
have long necks
survive better
 leave more offspring
who inherit their long
necks
 variation
 selection &

survival
 reproduction &
inheritance of
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Asking Questions
is a good adaptation!
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2006-2007
Comparative Anatomy
 Comparative Anatomy includes
Homologous and Analogous structures
as well as vestigial features.
 Comparisons of anatomical features in
different organisms often provides
evidence to support the theory of
evolution. As Organisms are often
classed together according to
similarities in their structures.
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Homologous Structures

Homologous structure are structures that share a common
origin but may serve different functions in modern species.
 These structures are evidence that organisms with similar
structure evolved from a common ancestor.
 Examples include the forelimbs of a variety of mammals.
For example, human, cat, whale and bat.
 These species show the same skeletal elements. (humerus,
radius and ulna)
 However these skeletal elements have been modified over
time to suit the different functions suitable for the type of
mammal.
 Homologous structures result from divergent evolution
meaning their ancestral lines started out fairly similar, but
evolved along different paths, becoming more different
over time.
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•
Structures that are similar due to evolutionary origin,
-forearm bones of humans, birds, porpoises, and
elephants, are called homologous.
Structures that evolve separately to perform a similar function
are called analogous.
-The wings of birds, bats, and insects, for example, have
different embryological origins but are all designed for flight.
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Analogous Structures
 Analogous structures are a
contrast to homologous
structures.
 They serve the same function
between organisms but are
different in internal anatomy.
 Such as the wings of birds
and butterflies.
 These structures are of no
use in classifying organisms
or in working out their
evolutionary relationships
with each other.
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Vestigial Organs
 Vestigial organs provide further evidence for evolutionary
change.
 These organs are usually dwarfed and useless to the
organism.
 Examples of these include:
 The human appendix which is useless in humans,
but in other mammals it is necessary for digestion of
high cellulose diet.
 The human external ear muscles.
 The tail bone.
 Wisdom teeth.
 Some snakes have skeletal limbs.
 Even though organisms have these organs there is no
significant disadvantage to the organism.
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Embryology
 Embryology of organisms can be used to demonstrate the
existence and even degree of relatedness of organisms.
 In the early stages of development embryos of many
organisms look extremely similar.
 Embryos in mammals, birds, reptiles and fish have many
body similarities in common
 As the embryos develop further, the similarities gradually
disappear.
 This embryonic resemblances indicated that organisms are
related by their common ancestors.
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Similarities in Embryos
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Summary
 The layers of fossils in sedimentary rock shows the
progression of organisms through time.
 Homologous structures are structures that are similar in
appearance but not In function.
 Analogous structures are structures that are similar in
function but not in appearance.
 Vestigial Features are organs and structures that still
remain in animals, however they serve no function or
purpose in the organism.
 Embryology shows the similarities that organisms have at a
very early stage of development.
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