Download Natural Selection

Characteristic #6
All organisms respond to
changes in external
environment while
maintaining constant
internal environment.
• Inside is controlled chemically and physically.
• External responses:
– Skin tans in response to sunlight
– Roots change direction moving towards water
– Dogs pant in the heat
Evolution
Change over time
Charles
Darwin
• A naturalist who served aboard research ship
called “The Beagle” in 1831
• Observed bird and animal species in Galapagos
• Made observations about species characteristics
• Published “On the Origin of Species”
• Formulated theory of evolution by natural
selection
• Birds on different
islands had different
shaped beaks.
• Each beak style seemed
perfect for island’s food
supply.
• Darwin speculated that
each species of bird had
adapted to utilize the
food in its environment.
• Darwin explained these
changes with his theory
of evolution by natural
selection
Darwin’s
Observations
Evolution
Gradual changes in a population
or species over time
Natural Selection
The way these changes occur
Patterns of Evolution
Artificial selection
When humans breed organisms with
certain traits to produce offspring
with those traits.
Examples: dog species, draft horses, garden
variety flowers
Artificial
Selection
Dairy cows have been bred by artificial selection for
large udders and high milk production. As a result, many
cows have udders so large that they cannot walk without
swinging their legs out to the side.
Patterns of Evolution
Natural selection
When organisms that have favorable
adaptations are selected by nature
survive and reproduce.
Examples: colors which blend in with habitat,
prehensile tail, beaks adapted to local food
sources
Adaptations
Opposable thumb: thumb that
allows grasping and holding
Evolution by Natural Selection
In nature, organisms with the best
characteristics for surviving in an
environment will live longer and pass
those characteristics on to more
offspring. Eventually more of the
population will have these adaptive traits.
In nature, organisms produce too many
offspring for environment to support
Individuals will have a variety of characteristics
Individuals with good traits for survival will live and
reproduce more than others, passing on the good
traits to their offspring.
The population will eventually change in appearance
as this trait becomes more common.
Two Types of Natural Selection
Divergent Evolution
When related
species become
more and more
different due to
different niches
Adaptive Radiation
One type of divergent evolution
One species in a new environment
changes into many new species, each
adapted to a particular food source and
way of life.
Divergent Evolution of
Hawaiian Honeycreepers
• A small bird migrated to an island
• Island had diverse ecosystem
(insects, nuts, berries, flowers &
nectar, worms, leaves…
• Eventually, many species of birds evolved
• Each had features adapted for one niche
– Different coloration
– Different beak shapes
– Different anatomical structures
Maui Parrotbill
`Amakihi
Breaks apart wood and
then pries out insect
larvae.
Eats insects and
nectar.
`Akohekohe
Feed primarily on insects
and nectar from `ohi`a
blossoms
Maui Creeper
Eats insects among the
leaves and branches.
The Po`ouli
Finds insects, spider and snails
under leaves and bark
'I'iwi Honeycreeper
Eats the nectar stored in
deep-throated flowers.
Homologous structures
• Structures from related individuals that have
become modified for a particular environment.
• Usually result from divergent evolution.
Second Type of Natural Selection
Convergent evolution
When two or more
unrelated species
become more similar
due to similar
environments.
Organisms that have converged
due to similar environments
Analogous structures
• Structures on unrelated
species that are similar due to
similar functions.
• Analogous structures result
from convergent evolution.
Analogous Structures
Fish/shark and
Whale
• No common ancestry
• Similar body shape
and streamlining due
to common
environment.
• Structures have
become similar due to
convergent evolution.
Evidence for Evolution and
Relatedness of Species
Types of evidence that shows if species
are related include:
– Fossil evidence
– Comparative anatomy
– Biochemistry
– Chromosomes
– Embryology
– Microevolution
What are Fossils?
• Fossils - traces of dead organisms
• Fossils can be molds, footprints,
imprints, bones or entire organisms
Determining the Age of a Fossil
• Absolute age: carbon dating relies on
radioactive elements, which tell the actual
age of the fossil.
• Relative age: the age of a fossil can be
predicted by its location in a rock column
Fossil Evidence
•
•
•
Fossils can be found
in sedimentary rock
(mud, sand or clay).
Older fossils are
found lower in rock
Newer fossils are
found closer to the
surface
Sedimentary Rock
Geologic column: a tall segment with
many layers of sediment
Fossils on the bottom of the column are
older than those on the top.
Oldest
Youngest
Using Fossils to Understand Relationships
• The bone structure in fossils indicates how closely
related organisms may be
• The sequence of development the horse was
determined by the location in rock and the similarities
of the fossils
1. Hyracotherium
4. Merychippus
2. Orohippus
5. Pliohippus
3. Mesohippus
6. Modern day Equus
Comparative Anatomy
• Similar
anatomy
indicates
closer
relationships
• Homologous
structures
show closer
relationships
Crocodile
forelimb
Whale
forelimb
Bird
wing
Vestigial Structures
• Structures present in ancestors but no longer
needed.
• For example:
- appendix
Snake
Whale
- tailbones
humans (4)
gorilla (?)
- ear muscles
- pelvic girdle
Snakes
Whales
Biochemistry
• ALL living organisms contain the same
genetic code
– the same four DNA nucleotides (AGCT)
– The same 20 amino acids
• More closely related species have more
similar:
– Nucleotide sequences in DNA
– Amino acid sequences in their proteins
All life uses the same
genetic code
In every living species,
the codon UAC in RNA
codes for the amino acid
tyrosine
Cytochrome C
•
•
Cytochrome c is an enzyme in the
mitochondria of the body.
Humans have 104 amino acids in
cytochrome c
•
•
•
•
Chimpanzees have the identical aa
sequence as humans
Dogs differ in 13 of the amino acids
Snakes differ by 20 amino acids.
The more closely related the species, the
more amino acids they will have in common.
Chromosomes
Closely related
species have
similar gene
sequences on
chromosomes
• Genetically,
chimpanzees
are 98.5
percent
identical to
humans.
• However, the
differences
between the
species are
profound.
• Small gene
differences
make for huge
differences in
traits
Genetic Differences
between
Chimpanzees and
Humans
Embroylogy
• Embryos from different species show similar
features due to shared ancestry
• All vertebrates have
– Tails
– Gill pouch
Chick
Human
Microevolution
watching evolution occur
Sometimes, evolution occurs on a small
scale that we can watch over a period of a
lifetime
Microevolution
In England, the industrial revolution resulted in heavy pollution
and soot-covered surroundings. Eventually the trend was
reversed and the pollution was reduced.
Researchers studied how a species of moth with two forms
adapted to its changing environment.
In each environment, the form that was best
camouflaged lived longer and had more offspring
than the other, and eventually became the most
common form.
Microevolution
watching evolution occur
The Moth study is one example of
microevolution
Physiological adaptations can develop rapidly
Non-resistant
bacterium
Antibiotic
Resistant
bacterium
The bacteria in a
population vary in
their ability to resist
antibiotics.
When the population is
exposed to an antibiotic,
only the resistant
bacteria survive.
The resistant bacteria
live and produce more
resistant bacteria.
Non-resistant
bacterium
Antibiotic
Resistant
bacterium
Today, penicillin no longer affects as many
species of bacteria because some species
have evolved physiological adaptations to
prevent being killed by penicillin.