Transcript in natural selection

Charles Darwin (1809-1882)
Sailed around the world 1831-1836
What did Darwin’s
Travels reveal ?
• The diversity of living
species was far greater
than anyone had
previously known!!
• These observations led
him to develop the
theory of evolution!!
How did tortoises and birds differ
among the islands of the
Galapagos?
• Each island
had its own
type of
tortoises
and birds
that were
clearly
different
from other
islands
Galapagos
Turtles
Evolution is when organisms change over time.
So, modern organisms descended from ancient
ones
Evolution is a Theory – Just like
Gravity!
• Evolution is a well
supported
explanation of
phenomena that have
occurred in the
natural world
• A theory in science is
a well tested
hypothesis, not just a
guess BUT an
explanation to an
observation
Theories
• Theories have been tested many times by
many scientists,
• A theory BEST explains a certain
observation
• People have tried to refute Charles
Darwin’s theory of evolution, but so far
have been unsuccessful, therefore it
remains
Who influenced
Darwin’s ideas?
Geologists:
Hutton and Lyell
Fundamentalists said that the
earth was around 6000 years old
Hutton and Lyell argued that the
earth is many millions of years
old b/c
– layers of rock take time to form
– processes such as volcanoes
and earthquakes shaped the
earth and still occur today
Lamark
Theory of acquired characteristics
•
Lamark said
organisms acquired
traits by using their
bodies in new ways
•
These new
characteristics were
passed to offspring
•
Lamark was totally
wrong!
Malthus
• Reasoned that if the
human population
continued to grow
unchecked, sooner or
later there would be
insufficient living space
and food for everyone
Darwin finally
published his
ideas in 1859
• Other naturalists
were developing
the same theory
that Darwin did.
• Even though he
was afraid of the
Church’s reaction
to his book he
wanted to get
credit for his
work.
Artificial Selection
• nature provides variation, humans select
variations that are useful.
• Example - a farmer breeds only his best
livestock
Natural
Selection
• The traits that
help an organism
survive in a
particular
environment are
“selected” in
natural selection
Natural Selection and Species
Fitness
• Overtime, natural selection results in
changes in the inherited characteristics
of a population.
• These changes increase a species
fitness (survival rate)
Descent with Modification
• Each living
species has
descended
with changes
from other
species over
time
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than
survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass
those advantages to their children
5. Species alive today are descended with
modifications from common ancestors
Evidence of Evolution
1. Fossil Record
2. Geographic Distribution of Living
Species
3. Homologous Body structures
4. Similarities in Embryology
Evidence of
Evolution
Fossil Record provides
evidence that living
things have evolved
Fossils show the history
of life on earth and
how different groups
of organisms have
changed over time
Relative vs.
Absolute
Dating
Relative Dating
• Can determine a
fossil’s relative age
• Performed by
estimating fossil age
compared with that of
other fossils
• Drawbacks – provides
no info about age in
years
Absolute dating
• Can determine the
absolute age in
numbers
• Is performed by
radioactive dating –
based on the amount
of remaining
radioactive isotopes
remain
• Drawbacks - part of the
fossil is destroyed
during the test
Carbon-14 Dating
Fossil Formation SG
Primate Fossils
Australopithecus
Homo erectus
Homo sapien
Primate
Brain
Capacity
Primate Bone structure
Human Relatives
Australopithecus
afarensis
Homo habilis = handy human
1.5 to 2 mya
Homo erectus
1.6 mya
bipedal
Cro-Magnon
35,000 to 40,000 ya
Neanderthals
35,000 to 100,000 ya
Modern Homo sapien
(fully modern fossils 100,000 ya)
Evidence of
2. Geographic
Distribution of Living
Species
Similar animals in
different locations
were the product of
different lines of
descent
Evolution
Evidence of
Evolution
Turtle
Homologous Body
Structures
– Structures that have
different mature
forms but develop
from the same
embryonic tissues
Alligator
Bird
e.g. Wing of bat,
human arm, leg of
turtle
Homologous Body Structures
Vestigial Organs
– traces of homologous organs in other
species
– Organ that serves no useful function
e.g. Appendix
Evidence of
Evolution
Similarities in
Embryology
–
In their early
stages of
development,
chickens,
turtles and rats
look similar,
providing
evidence that
they shared a
common
ancestry.
Embryological development
Natural Selection
• Acts on PHENOTYPE not genotype
• Only the Phenotype of an organism
determines if the organism survives
Natural Selection
• The allele for long tongue (L) is dominant
over the short tongue allele (l). Lizards
that have long tongues have a better shot
of surviving because the are better at
catching dinner (flies).
• Of the lizards listed below, which have a
better shot of surviving?
LL, Ll, ll
Natural Selection
• The allele for long tongue (L) is dominant over
the short tongue allele (l). Lizards that have
long tongues have a better shot of surviving
because the are better at catching dinner (flies).
• Of the lizards listed below, which have a better
shot of surviving?
LL, Ll, ll BOTH LL and Ll have long tongues, so
natural selection acts on the phenotype NOT the
genotypes
Natural Selection
• Each finch is best
adapted to feed
itself in the
environment that
they lived in.
• Does it matter if
they are
homozygous or
heterozygous for
the trait?
Recessive Lethal Alleles
• An allele that is lethal will cause a death in
an individual if homozygous for the allele
• Example:
• Tay-Sachs Disease, is an autosomal
recessive genetic disorder
• Tay-Sachs disease is caused by a genetic
mutation on the HEXA gene on
chromosome 15
Recessive lethal diseases
• Recessive lethal diseases are not very
common, even though an organism with a
lethal homozygous disorder will die before
reproducing the lethal allele remains in the
gene pool…
• Why?
How do you Get Tay-Sach’s
disease?
“Carriers”
• A “carrier” of a disease is a heterozygous
individual. The individual expresses the
non-lethal normal allele BUT still carries a
copy of the lethal allele.
• Two heterozygous individuals have a ¼
chance of getting a homozygous recessive
individual, try the cross.
Mutations
• Can be beneficial because the create
genetic variety
• Can be harmful because they can lead to
an abnormal protein production
• ARE random
As the environment changes, so
must the traits that are best fit for it
• How does change occur?
– Mutations
– Crossing Over during Prophase I of meiosis
– Sexual Reproduction
The greater the genetic variety of a population
the better the chances of that population
surviving change
When the Earth changes too
quickly
• When the environment changes quickly,
organisms might not survive and may go
extinct because they may no longer be fit
for the “new” environment
• Having a diversity of organisms gives the
species a better chance of some of its
organisms surviving
• Some examples…
Antibiotic resistant bacteria
Pesticide Resistance
Dinosaur extinction
Mass Extinction
Global Warming, are we heading
towards another mass extinction?