Download Notes #29

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 living 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
process of evolution 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 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.
Darwin’s Observations Variation
• Observed a variation
of traits among similar
species that 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
• Evolution Occurs
• BUT HOW???????
Darwin proposes
Theory of Natural Selection as the
Mechanism for Evolution
Four Main Principles to Theory :
• Overproduction
• Variation
• Adaptations for survival are selected by
nature
• Descent with Modificaiton
1.Overproduction
• Organisms have more offspring than the
environment can support – not all offspring
will survive
2. Variation
• Population – all the individuals of a
species that live in a particular area.
• A variation of traits exists within the
individuals of a population
• Individual differences are due to inherited
or mutated genetic information
• 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.
Those organisms will likely:
*Live the longest
*Produce more offspring with the inherited trait
“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
4. Descent with modifications
• Survivors have traits that are better suited
to living in 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 this causes a change to the
population and thus ________________
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 only 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 better adapted
forms.
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
•
•
•
•
•
Fossils
Comparative Anatomy
Cell Structure
Embryology
Molecular Comparison
Fossil Record
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)
• Protein synthesis same process in all cells
• All cells have membranes of 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
Individuals within Populations are
Genetically Different
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
• Stored in 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
•
Brown hair 1:3
Reasons for loss of variation
• Bottleneck effect – destructive event
leaves few individuals and reduces gene
pool
• Ex. Overhunting
• Ex. 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
Other causes of Evolution
(other than Natural Selection)
• Geographic Isolation
• Reproductive Isolation
* Temporal – organism breed at different
times
*
Causes of Speciation
The Creation of New Species
• Geographic isolation of populations
• Can lead to
• Reproductive isolation of population
• Can lead to
•
•
New Species
(unable to breed when together)
Geographic Isolation
• Members
of a
population
may
become
isolated
from one
another by
geographic
boundaries
like
mountains,
rivers or
even
oceans
Reproductive Isolation
Adaptive Radiation
New Species Evolve due to adapting to
being in different environments
V. Evolutionary Time Frames
A. Gradualism: species descend from a common
ancestor gradually as the change in minor ways
over a long period of time.
B. Punctuated Equilibrium a newer theory
developed by Stephen Jay Gould states that
species remain fairly constant over long periods
of time until a great change in their environment
cause relatively rapid speciation.
Convergent Evolution
Divergent Evolution
(Adaptive Radiation)
• 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