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Darwin & Evolution
Natural Selection
Insect eaters
Seed eaters
Bud eater
Regents Biology
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
 British naturalist
Regents Biology
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
Regents Biology
Voyage of the HMS Beagle
 Stopped in Galapagos Islands
500 miles off coast of Ecuador
Regents Biology
Most of animals on the
Galápagos live nowhere else
in world, but they look like
species living on South
American mainland.
Regents Biology
Darwin found…many unique species
Many of Darwin’s observations made
him wonder… Why?
Regents Biology
Darwin found…clues in the fossils
Darwin found:
Evidence that creatures
have changed over time
present day Armadillos
ancient Armadillo
Regents Biology
Darwin found:
Different shells on tortoises on different islands
Darwin asked:
Is there a relationship
between the environment
& what an animal
looks like?
Regents Biology
Darwin found… birds
Darwin found:
Many different birds
on the Galapagos
He thought he found
very different kinds…
Regents Biology
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
Darwin asked:
If the Galapagos
finches came from the
mainland, why are they
so different now?
Regents Biology
The finches cinched it!
Darwin found:
The differences
between species of
finches were
associated with the
different food they
Regents Biology
different beaks are
inherited variations
as adaptations
that help
birds compete
for food
A flock of South
birds survive
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
Regents Biology
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
Regents Biology
From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
tree finch
tree finch
Insect eaters
Seed eaters
tree finch
Regents Biology
Bud eater
natural selection for best
survival & reproduction
Earlier ideas on Evolution
 LaMarck
evolution by acquired
 creatures developed traits
during their lifetime
 give those traits to their
 in reaching higher
leaves giraffes stretch their
necks & give the acquired
longer neck to offspring
not accepted as valid
Regents Biology
Darwin’s view of Evolution
 Darwin
giraffes that already
have long necks
survive better
 leave more offspring
who inherit their long
 variation
 selection &
 reproduction &
inheritance of
Regents Biologymore fit traits
Asking Questions
is a good adaptation!
Regents Biology
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.
Regents Biology
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
 Homologous structures result from divergent evolution
meaning their ancestral lines started out fairly similar, but
evolved along different paths, becoming more different
over time.
Regents Biology
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.
Regents Biology
Analogous Structures
 Analogous structures are a
contrast to homologous
 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.
Regents Biology
Vestigial Organs
 Vestigial organs provide further evidence for evolutionary
 These organs are usually dwarfed and useless to the
 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.
Regents Biology
 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
 This embryonic resemblances indicated that organisms are
related by their common ancestors.
Regents Biology
Similarities in Embryos
Regents Biology
 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.
Regents Biology