Transcript The Living Environment

Evolution
• Evolution is change over time.
• The Theory of Evolution states
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that all organisms share a
single common ancestor and
have evolved over time.
It also states that this has
occurred largely due to
changes in environmental
conditions that have led to a
necessity for organisms to
change and adapt or go
extinct.
Darwin’s Theory of Natural Selection
• In 1831, Charles Darwin set
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sail on the HMS Beagle as the
ship’s naturalist.
His job was to collect
biological and geological
specimens.
After traveling from England
across the Atlantic and
collecting specimens along
the eastern and western
coasts of South America, the
ship landed in the Galapagos
Islands.
Darwin’s Theory of Natural Selection
• Although Darwin only spent a few weeks exploring the
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Galapagos Islands, he later said that he made his
greatest discoveries there, which led him to write his
book, The Origin of Species.
The Galapagos Islands are a volcanic archipelago
located 600 miles off the coast of Ecuador.
Darwin’s Theory of Natural Selection
• In 1859, Darwin publishes
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his work in which he
describes how species
originate by means of
natural selection.
Natural selection is the
process where heritable
traits that make it more
likely for an organism to
survive long enough to
reproduce become more
common over successive
generations of a population.
Darwin’s Theory of Natural Selection
• Natural selection, also
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known as “survival of the
fittest,” refers to the
selection by nature for
the most fit, or most well
adapted members of a
species to survive.
This selective process
allows for only the best
traits to be passed on to
the next generation.
Darwin’s Finches
• After studying a variety of birds on the Galapagos
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Islands, Darwin developed his Theory of Natural
Selection.
Darwin initially thought he had been studying a variety
of birds on the islands, but actually they were all
different species of finch, adapted for various
environments depending on the available food
resources.
He decided that specific traits
were selected for naturally,
depending on which traits were
advantageous in a particular
ecosystem.
Darwin’s Finches
•Darwin found that the beaks of
finches varied from island to
island depending on the food
source available for each finch
population.
Galapagos Giant Tortoises
•Darwin missed the opportunity to study Galapagos
tortoises but was told by the vice governor that he could
tell which island a tortoise was from by the shape of its
shell.
•Dome shelled tortoises feed off the ground while
saddleback tortoises can extend their necks to feed from
higher vegetation.
Galapagos Giant Tortoises
Evidence of Evolution
• The fossil record offers some of the most significant
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evidence of evolutionary change.
Fossils have been discovered that give evolutionary
biologists clues into what features were present in
ancient organisms and how those organisms may
have evolved into
modern organisms.
Archaeopteryx is an
extinct organism
that shares
characteristics of
both birds and
reptiles.
Fossil Evidence
•Fossils discovered around the world from the tops of
mountains to the bottom of the oceans have helped
prove that organisms have changed over time.
• Fossil teeth of Megalodon, an extinct ancestor of the
Great White Shark, have been found on the ocean floor
around the globe, proving the shark was once much
larger, like most
top predators of
the time.
Comparative Anatomy
• Anatomically similar structures inherited from a
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common ancestor are called homologous structures.
Evolution predicts that an organisms body parts are
more likely to be modifications of ancestral body parts
than they are to be
entirely new
features.
Therefore, homology
proves common
ancestry, which in
turn proves evolution
has occurred.
Comparative Anatomy
• Although homologous structures prove common
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ancestry, analogous structures prove otherwise.
The wings of a bat, bird, and butterfly are analogous,
or structurally different; proving that functionally
similar features can
evolve independently
in similar
environments.
Vestigial Structures
•Vestigial structures are structures that still exist in a
population but no longer serve a function.
•Evolutionary theory predicts that features of ancestors
that no longer have a function for that species will
become smaller over time until they
are lost.
Comparative Embryology
• Comparing embryos of
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vertebrates during
early stages of
development shows
homology and can
therefore show
common ancestry.
Later stages also show
homology which can
be used to develop a
phylogeny, or
ancestral tree.
Comparative Biochemistry
• Evolutionary theory predicts that molecules in species
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with a recent common ancestor should share certain
ancient amino acid sequences.
The more closely related the species are, the greater
number of sequences will be shared.
Comparing DNA and RNA
can yield strong evidence
of organisms sharing a
common ancestor.
Phylogeny
• A phylogeny is an ancestral
tree illustrating common
ancestry.
•Phylogenies can also
illustrate where in
evolutionary history a
particular trait was acquired
by the proceeding species.
•The diagram is known as a
cladogram.
Defining a Species
• A species can be defined by any
one of three ways:
Morphological Species
Concept: if they look the same
they are the same species.
Biological Species Concept: if
they can mate and produce
viable offspring they are the
same species.
Phylogenetic Species Concept:
if they share an immediate
ancestor they are the same
species.
Speciation
• Speciation, or the birth of a new
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species, occurs when a
population diverges and becomes
reproductively isolated.
A population may diverge and
become reproductively isolated
due to a geographic barrier such
as a newly formed mountain
range or river or due to the
migration of a population into a
new area.
Geographic isolation is not
always necessary for speciation.
Speciation due to Geographic Isolation
•When a population is divided and reproductively
isolated, if enough time passes, the two groups of
organisms will no longer be able
to reproduce due to genetic
variations as a result of meiosis,
and are therefore considered to be
two new species.
Co-evolution
• Many species evolve in close
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relationships with other
species. This is known as
co-evolution.
In some cases, two species
will co-evolve to maintain a
mutualistic relationship.
In other cases a coevolution arms race will
occur, whereby each species
is continually evolving to
defend itself from the other.