Transcript Natural selection

Darwin’s Theory of Evolution *
• Evolution, is change over time, OR is the
process by which modern organisms have
descended from ancient organisms.
• A scientific theory is a well-supported
testable explanation of phenomena that have
occurred in the natural world.
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
Evolution is when organisms change over time.
So, modern organisms descended from ancient
ones
Charles Darwin: Father of evolution.*
Sailed around the world 1831-1836
How do you think Darwin came up with
his theory?
Voyage of the Beagle
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!!
Patterns of Diversity
• Darwin visited Argentina and Australia which had
similar grassland ecosystems.
– those grasslands were inhabited by very different
animals.
– neither Argentina nor Australia was home to the sorts of
animals that lived in European grasslands.
Living Organisms and Fossils.*
• Fossils are the preserved remains of
ancient organisms.
• Some of those fossils resembled organisms
that were still alive today.
Living Organisms and Fossils
• Others looked completely unlike any creature he
had ever seen.
• As Darwin studied fossils, new questions arose.
– Why had so many of these species disappeared?
Mass extinction
How were they related to living species?
Observation from their fossils.
Fossils
Types of fossils
Cast
Trace fossils
Frozen or amber
mold
Imprints
Petrified fossils
Imprint
The Galapagos Islands
• A group of islands of
the west coast of
South America
• The islands are close
together but have
very different climates
• Darwin noticed that
the characteristics of
many plants and
animals varied among
islands.
The Galapagos Island
• The smallest, lowest islands were hot,
dry, and nearly barren-Hood Islandsparse vegetation
• The higher islands had greater rainfall
and a different assortment of plants
and animals-Isabela- Island had rich
vegetation.
Animal on the Galapagos Islands
Land tortoises
Blue footed booby
Galapagos finches
Marine Iguanas
The Journey Home
• Darwin Observed that
• Many islands close together with
different climates.
• Characteristics of many plants and
animals vary greatly among the
islands
Darwin finally published his ideas in 1859
in his book “The Origin of Species” that
summarized all his findings from his trip
around the world.
Lamarck
Theory of acquired characteristics
Lamarck said organisms acquired traits by using their
bodies in new ways
These new characteristics were passed to offspring
Lamarck was totally wrong!
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
information about age
in years
Primate Fossils
Australopithecus
Homo erectus
Homo sapien
Homo habilis =
handy human
1.5 to 2 mya
Homo erectus
1.6 mya
bipedal
Modern Homo sapien
(fully modern fossils
100,000 ya)
2. Geographic Distribution of Living
Species
Similar animals in different locations were
the product of different lines of descent
Homologous body structures
Structures that have different
mature forms but develop from
the same embryonic tissues.
Wings and legs all descended from
fish fins.
Turtle
Alligator
e.g. Wing of bat, human arm, leg of
turtle
Bird
Homologous Body Structures
Vestigial Organs
– Vestigial structure: It is a structure
without function or no use.
e.g. Appendix in man
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
Evolution by Natural Selection
• Selection means to choose
What do you think natural selection mean?
(“Nature chooses”, chooses what?
Best adaptations for survival)
The Struggle for Existence-members of each
species have to compete for food, shelter, other
life necessities in order to survive.
Survival of the Fittest-Some individuals are better
suited for the environment. Organisms with most
favorable adaptation will survive.
Natural Selection
Natural selection is the process by which individual organisms with
favorable traits are more likely to survive and reproduce.
Fitness is the ability of an individual to survive and reproduce
in its specific environment.
Adaptation: an inherited characteristic that increases an
organism’s chance of survival.
Artificial Selection
Nature provides variation, humans select variations
that are useful.
Example - a farmer breeds only his best livestock.
Components of Natural
Selection
• Not all individuals will
be able to reproduce.
• Due to environmental
issues, illness, etc…
• DIFFERENTIAL
REPRODUCTION
Birds eat green beetles, not
brown ones.
What’s
Left?
What’s the
end result?
Components of Natural Selection
The brown
trait has a
genetic
basis.
The brown beetles
that are left will
mate and have
brown offspring.
This is called
HEREDITY.
• Finally, the brown trait
(which is more
advantageous) allows
the beetle to survive in
order to reproduce.
• Eventually, all beetles in
this population will be
brown.
• This PHENOTYPE has
been SELECTED over
the green phenotype.
Image courtesy of http://evolution.berkeley.edu/evolibrary/article/_0_0
Descent with Modification
• Descent with Modification- Natural selection produces
organisms that have different structures, establish
different niches or occupy different habitats. This
causes today’s species to look different from their
ancestors.
Common Descent- were derived from common ancestors
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.
Evolution of Populations
Occurs when there
is a change in
relative frequency
of alleles
VOCABULARY REVIEW
• Evolution –
change over time
• NATURAL SELECTION –
Individuals better adapted to the
environment are able to survive and
reproductive.
– “SURVIVAL OF THE FITTEST”
NEW VOCABULARY
• POPULATION –
Group of individuals of same species
that interbreed.
• GENE POOL –
Common group of all genes present in a
population.
Variation and Gene Pool
Combined genetic
information of all
members.
Allele frequency is
number of times
alleles occur in the
population.
Evolution: Any change in the
relative frequency of
alleles in a population
Single-Gene vs. Polygenic Traits
Single-Gene trait: any trait controlled by one gene (example:
tongue rolling)
Natural selection on single-gene traits can lead to change in
allele frequencies and thus evolution. Distinct phenotype
Polygenic traits: any trait controlled by two or more genes
(example: height in human) Many Phenotypes
Natural selection can affect the distribution of
phenotypes in any of three ways:
1.Directional selection- Individuals at one end of
the curve have higher fitness than those in the
middle. (Example: seed size and birds beak size)
2. Stabilizing selection-Individuals near the
center of the curve have higher fitness
than those at either ends of the curve.
(Example: weight of human infants at
birth).
3.Disruptive selection-Individuals at the
upper and lower ends of the curve have
higher fitness than those near the
middle. (Eample: seed size and bird beak
size).
PHENOTYPE SELECTION
• http://www.youtube.com/watch?v=aTftyFb
oC_M
• http://www.youtube.com/watch?v=Fvhk4H
-3Z5g
Natural Selection on Polygenic Traits
Genetic Variation
Gene Flow
Movement of genes
from one population to
another.
Mutation
Sexual
Reproduction
Sexual reproduction
causes new
combinations of genes.
Changes in DNA
Sources of genetic Variation in Populations
processes can
lead to this:
Mutations change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
What causes genetic variation?
• The forces that causes population
and species to evolve are:
1. Natural selection
2. Migration
3. Genetic drift
4. Mutation
Genetic Drift
• Genetic drift occurs only in small population
What is genetic drift?
• It is a random change in allele frequency
causes an allele to become common.
Effects of genetic Drift
• Genetic drift has two main effects on
population:
1.
Bottle necking effect
2.
Founder effect
Bottle necking effect
Reduction in a small population due
to chance event.
The surviving population does not
represent the true original
population.
http://www.youtube.com/watch?v=6MJPhlkbUlA
Use white/brown beans to explain
this.
Founder Effect:
genetic drift due to the
migration of a small subgroup of a population.
(example: fruit flies migrating from mainland to
different Hawaiian islands and)
http://www.youtube.com/watch?v=5J1gdfgFhmg
Hawaiian Honeycreepers
An example of adaptive radiation –
these species all diverged from a
common ancestor (founder species)
FOUNDER SPECIES
Conditions needed for Genetic
Equilibrium
• Hardy Weinberg ‘s principle for the
population to remain constant:
1. Population must be large
2. There must be no mutation
3. No sexual selection
4. No struggle for survival
5. No movement into and out of the
popution(emmigration).
GENETIC EQUILIBRIUM
• http://www.youtube.com/watch?v=AU2XC
DMdR9k
• http://www.youtube.com/watch?v=AHkeo
OeV16g
SPECIATION
Speciation is the formation of new species
• As new species evolve, population become
reproductively isolated.
1. Reproductive Isolation – Members of two
population cannot interbreed & produce
fertile offspring.
ISOLATING MECHANISMS
Behavioral Isolation - capable of breeding but
have differences in courtship rituals (EX. Mead
Table 23.1a
Geographical Isolation – Separated by
geographic barrier like rivers ,mountains, or
bodies of water (ex: squirrel)
Temporal Isolation – Two or more species
reproduce at different times
ISOLATING MECHANISMS……..
2. Behavioral Isolation - capable of
breeding but have differences in
courtship rituals (EX. Meadowlarks)
3. Geographical Isolation – Separated by
geographic barrier like rivers ,mountains,
or bodies of water (ex: squirrel)
4. Temporal Isolation – Two or more
species reproduce at different times.
Table 23.1a