Transcript Principles of Evolution

Evidence for Evolution and the
Theories of Evolution that are
based on this evidence
What is Evolution?
Evolution – process of biological change by which
populations of organisms change over time and
become different than their ancestors.
Origins of Evolutionary
Theory
Scientific beliefs prior to the 1700’s:
• Earth was only 6000 yrs old and had not
changed since its creation
• Each species appeared individually on Earth
• Species could not go extinct
What is a Species?
A group of organisms that are similar
enough to reproduce and have fertile
offspring (fertile – able to have babies)
Origins of Evolutionary Theory
• 1700s -a time of great advances in
intellectual thought and discoveries
• By the 1800’s earlier ideas had been
replaced -The idea that organisms change
or evolve was more accepted.
• Although the idea of evolution was more
accepted, the actual mechanism or
method was unknown
Several people became famous
historical figures due to their
theories on how evolution occurs
Jean Baptiste LaMarck 1809
• Inheritance of Acquired Traits
Theory
• Organisms inherit the traits that
their parents developed or acquire
during their lifetime
• a.k.a “Use it or Lose it” Theory
Lamarkian Theory of Evolution
Example
• Giraffe’s stretch their necks when the reach
high for leaves.
• Over time their neck grows longer.
• The parent’s stretched neck gets passed
down to young.
Lamarkian Theory
• If I wear braces to straighten my teeth
then my children will have straight
teeth
• A man breaks his nose – his kids get
bent nose
Importance of Lamarkian Theory
• Though his ideas were discredited, they
were important in stimulating scientific
discussion about the mechanisms
(methods) of evolution.
Charles Darwin
• 1809-1882
• Age 22 takes a position as naturalist
about the HMS Beagle on a 5 year
mapping expedition of South America
and the Pacific Islands
• Collects hundreds of specimens and
made extremely detailed observations
of the natural world.
Voyage of the Beagle
Galapagos Islands
Darwin’s Observed Trait variations
• Observed a variations
in traits among similar
species
• Variations allowed
them to adapt to their
specific surroundings
• Ex. Finches bills
adapted to different
food types
Darwin’s Observations –
Fossil Evidence
Darwin’s Observation –
Geologic change
Darwin’s Conclusions
• Earth is older than 6000 years
• Present day life descended from older
forms of life
• Evolution Occurs
• BUT HOW???????
Darwin proposed the
Theory of Natural Selection
as the Mechanism for Evolution
• Video
4 Main Principles of the
Theory of Natural Selection
• Overproduction of offspring
• Variation in traits
• Nature “selects” the variations that provide
greatest chance for survival - Adaptations
• Descent with Modification – Darwin’s term
for evolution –organisms share a common
ancestor but descendants change over
time
1.Overproduction
• Organisms have more offspring than the
environment’s carrying capacity can
support – causes struggle for survival
2. Variation
• Individuals within a population show
variation in their traits.
• Variations are due to inheritance and
genetic mutations
• Offspring may inherit the trait variations
from their parents.
3. Adaptation
A particular trait form
may be adaptive or not
Adaptation – a
physical, physiological
or behavioral trait that
increases an
organism’s ability to
survive in its particular
environment.
Nature “selects” organisms with
traits best adapted to survival
• Nature “chooses” those
organisms with traits
that are best adapted to
survival.
Video
Those organisms will likely:
*Live the longest
*Produce more offspring with the inherited trait
Nature selects the traits
that are most adaptive for survival
• Nature DOES NOT make new traits –
genetic recombination in meiosis and
mutations are the source of new traits.
“Survival of the Fittest”
Which is more “FIT” to Survive?
• Fitness – measure of the ability to survive
and produce more offspring than others in
the population
Fitness is relative
• Fitness depends on the environment in
which the organism lives.
• The fittest genotype during an ice
age will not necessarily be the fittest
genotype when its over.
• Individual is not necessarily the
strongest, fastest, or biggest.
4. Descent with modifications
• Survivors have traits that are better suited
to surviving and passing down their traits to
their particular environment.
• They pass these adaptive traits to offspring.
• Individuals not as well suited to
environment die off and their genetic
information is lost to the population.
• **Over time a change in gene frequency
occurs as nature “selects” those that give
rise to the most adaptive phenotypes
• As nature “selects” those traits that are the
most adaptive for survival a change in the
population’s gene frequency occurs.
• Gene frequency is a measure of how
many individuals in the population have a
particular gene
• Over time this causes a change in the
population and thus evolution has
occurred.
Types of Selection
• Artificial Selection – Process of breeding
species to select for desired traits.
• (a.k.a Selective breeding)
In Artificial/Selective Breeding
humans are the selective agent
Natural Selection
• In nature, traits are selected when they
provide a survival advantage in the
environment at a specific time
• Nature is the selective agent.
Peppered moths
• Selection can lead to speciation - over
generations and time, new species will
evolve from older forms to forms better
adapted to the current environmental
conditions.
Creation of new Traits
• Natural Selection favors phenotypes/physical
traits that improve an organisms chance of
survival in a specific environment
• Natural Selection does NOT make new traits
or new genes
• New traits come from genes that are made
through mutations and crossing over in
meiosis
• Natural Selection in Action
• Why should you take take all your
antibiotic medicine even though you feel
better???
Evidence for Evolution
1. Fossils
2. Comparative Anatomy
1. Homologous structures
2. Analogous structures
3. Vestigial structures
3. Cell Structure
4. Embryology
5. DNA/ Molecular Comparison
Fossil Record –
Indicates Common ancestory
Comparative Anatomy
1. Homologous structures
* Same structure ; Different functions (homo=same)
* Suggests the species may be related/ have common ancestor.
Ex. Bats wing, human arm, and whale flipper bones.
)
Comparative Anatomy
2. Analogous structures
* Different structure Same
function
* May have developed
due to living in similar
conditions/ having
same environmental
pressures.
* Does NOT suggest the
species are closely
related
Ex. Bird wing and
Dragonfly wing
Comparative Anatomy
3. Vestigial structures – those that no longer serve a
present day useful function but still develop
•
Ex. Human appendix, tailbone (coccyx)
Cytological Comparisons
(Cell structure and function)
•
ex. Eukaryotic vs. prokaryotic cells
(nucleus)
(no nucleus)
**There are many similarities among even the most
different of cells
• Protein synthesis same process in all cells
• All cells have membranes madeof same basic
phospholipids
• Endosymbiotic Theory
Comparative Embryology
• Comparative embryology –
examination of differences
and similarities in embryo
development
• Similar structures during
development indicate shared
common ancestor .
• Ex. Gill slits – ocean
dwelling ancestor?
ex. Comparison of bird, fish
and early human embryos
Biochemical /Molecular Comparisons
•
Comparisons of molecules within species and between
species indicates common ancestors and relationships.
•
DNA comparison - Strongest evidence to support
evolution theory.
Human and Chimpanzee DNA more than 99% identical.
Humans and Gorillas and Baboons
95-97%
Human and Mice 80% identical DNA.
Ex. Cytochrome C, Humans differ from:
Monkeys - 1 amino acid
Pigs –
10 amino acids.
Fish –
21 amino acids
Molecular Comparisons
Phylogeny – study of determining
common ancestry between species
Phylogenetic Tree of Life –
suggests relationships and common
ancestry between species
Sources of Variation
• 1. Mutation
•
Change in the genetic code due to a
spontaneous change or an outside
mutagen
•
Beneficial if they result in a useful
adaptation
• 2. Genetic Recombination
•
Processes of meiosis and sexual
reproduction results in new combinations
of alleles in the offspring
Genetic Variation in a Population
• Greater genetic variation increases the chance
some individuals will survive changing
conditions
• A population’s gene pool – the combined alleles
of all individuals in population
• Allele frequency – how common the allele is
Ex. Achondroplasia 1:100,000 Americans
•
Brown hair 1:3 Americans
Causes of Evolution other than
Natural Selection
• Genetic Drift
* Bottleneck Effect
* Founder Effect
Genetic Drift
• Another mechanism or cause of evolution
• Random event (natural disaster, human
caused disturbance) causes change in
allele frequency
• Does not favor adaptations like natural
selection does
• Reduces genetic variety
Genetic Drift – Bottleneck Effect
• Bottleneck effect – destructive event
leaves few individuals, with a reduced
gene pool, to carry on the population
• The survivors may not have the most
adaptive genes
• Ex. Overhunting
•
Typhoon/Fire/natural disaster
Founder Effect
• Founder effect – when just a few
individuals create the foundation for a new
population – small gene pool ex. Amish
• Often results from migration, seed
dispersal by birds
Founder Effect
a few individuals from a population start a new population with a
differenct allele frequency than what existed in the original
population
Watch “ Mechanisms of Evolution”
Uploaded to Google Classroom – this shows
the many different events, in addition to
natural selection, that can result in evolution.
Patterns of Evolution
• Divergent Evolution (Adaptive Radiation)
• Convergent Evolution
• Coevolution
Divergent Evolution
Organisms share a common ancestor but
evolved differently to adapt to new environments
(Adaptive Radiation). Same internal structure.
Divergent Evolution
Common ancestor gives rise to new species.
Evolve due to adapting to different environments
Convergent Evolution
• Evolution produces species that are
similar in appearance and behavior due to
adapting to similar environments.
• No common ancestor
• Species have the same outer appearance
but their internal structures are different.
• Ex.a shark and dolphin have similar body
structures and live in similar environment,
but they are not related
Convergent Evolution
Coevolution
• A change in the genetic composition of
one species (or group) in response to a
genetic change in another – results in an
intimate connection between species
Darwin’s Moth – developed a
tongue that fits the flower perfectly;
The moth eats and the flower is
pollinated
Coevolution –
results in adaptations that increase the
interdependency between organisms
• Evolution is a fact – species do
change over time!!
• Natural Selection is a scientifically
supported theory that explains this fact.
• Decades of experimental and observational
evidence support Darwin’s theory of
Evolution by Natural Selection
• Video#1 What is Evolution?
• Video#2 Evidence for Evolution
• Video#3 What is Natural Selection