Transcript natural selection - Blue Valley Schools

Exploring Evolution
Key
Concept
There were theories of biological &
geologic change before Darwin.
Evolution
--the biological change process by
which descendants differ from their
ancestors
--a species is a group of organisms
that can reproduce &
have fertile offspring
Naturalists
in the 18th
Century
There were many naturalists:
--Linnaus: devised classification
system from kingdom to species
--Buffon: species have shared
ancestors rather than arising
separately
--Darwin: complex forms developed
from less-complex forms
--Lamarck: environmental change
leads to use or disuse of a structure
Theories of
Geologic
Change
Theories influenced Darwin’s theory.
--catastrophism: that the Earth has
been affected in the past by sudden,
short-lived, violent events
gradualism: that profound change is
the cumulative product of slow but
continuous processes
--uniformitarianism: that processes
operating on the Earth now have
always operated in the past
Key
Concept
Darwin’s voyage provided insight on
evolution.
Darwin
Observed
--differences among island species
--differences in physical traits
(variation)
--tortoises in areas of taller plants
have longer necks & legs
--finches in areas with hard-shelled
nuts have strong beaks
Darwin
Observed
--fossil & geologic evidence for an
ancient earth
--fossils of extinct animals that
resemble modern animals
--fossil shells high up in the Andes
mountains
--land move up
from underwater
during an earthquake
Adaptation
Video:
https://www.youtu
be.com/watch?v=K
DPLig4lMFo
Adaptation is a feature that allows
an organism to better survive in its
environment.
--species adapt to their
environment
--adaptations can lead to genetic
change in a population
Key
Concept
Darwin proposed natural selection
as a mechanism for evolution*.
Natural
Selection
--a mechanism by which individuals
that have inherited beneficial
adaptations produce more offspring
--the struggle for survival due to
limited resources eliminates less
desirable traits
--Darwin proposed that adaptations
arose over many generations
*Darwin’s theory
of evolution
based on the
ideas of variation
and natural
selection.
Natural
Selection
--acts on existing variation
--can act only on traits that already
exist
--structures take on new functions
in addition to their original function
five digits
wrist bone
Key Insights
--Darwin noticed a lot of variation
in domesticated plants & animals
--artificial selection is the process by
which humans select traits through
breeding
--heritability is the ability of a trait
to be passed to the next generation
neck feathers
crop
tail feathers
Four Main
Principles of
Natural
Selection
*ability to
contribute to
the gene pool
of the next
generation
--variation: differences in physical
traits
--overproduction: many offspring
but only fittest survive
--adaptation: best traits passed on
--descent w/ modification: best
traits become more common in
future offspring.
Fitness: is the measure of survival
ability & ability to reproduce.
Key
Concept
Evidence of common ancestry
comes from many sources.
1) Fossils
--fossils provide evidence
--fossils in older layers are more
primitive than those in upper layers
2) Geography
The study of geography provides
evidence of evolution.
--island species most closely
resemble nearest mainland species
--populations can show variation
from one island to another
3) Embryology
Embryology provides evidence of
evolution.
--identical larvae, different adult
body forms
--similar embryos, diverse organisms
Larva
Adult crab
Adult barnacle
4) Anatomy
The study of anatomy provides
evidence of evolution.
--homologous structures are similar
in structure but different function
--homologous structures are
evidence of a common ancestor
Human hand
Mole foot
Bat wing
More
Anatomy
--analogous structures have similar
function
--analogous structures are not
evidence of a common ancestor
Fly wing
Bat wing
5) Vestigial
structures
Structural patterns are clues to the
history of a species
--vestigial structures are remnants
of organs or structures that had a
function in an early ancestor
--ex) ostrich wings are examples;
whale pelvis, “snake hips”
Humans-appendix, coccyx, muscles
in the ear, goose bumps
Video:
https://www.youtube.com/watch?v=rFxu7NEoKC8
Key
Concept
New technology is furthering our
understanding of evolution.
Paleontology is the study of fossils
or extinct organisms.
--provides evidence to support
evolution
Genetic
Evidence
Molecular & genetic evidence
support fossil & anatomical
evidence.
--two closely related organisms
have similar DNA sequences
Genetic
Evidence
Pseudogenes are sequences
providing evidence of evolution.
--no longer function
--carried along with functional DNA
--can be clues to common ancestor
Hox genes indicate a very distant
common ancestor.
--control development of structures
--molecular fingerprinting reveals
similarities among cells of different
organisms
Unifying
Theory
Evolution unites all fields of biology.
--Scientist from any fields
contribute to the understanding of
evolution.
--The basic principles of evolution
are used in many scientific fields.
Key
Concept
A population shares a common gene
pool.
Genetic variation increases the
chance that some individuals will
survive.
--leads to phenotypic variation
--necessary for natural selection
--stored in a population’s gene pool
--made up of all alleles in the pop.
--offspring have allele combinations
Allele
Frequencies
Allele frequencies measure genetic
variation.
--measures how common allele is in
population
--can be calculated for each allele in
the gene pool
Genetic
Variation
Genetic variation comes from
several sources.
1) Mutation is a random change in
the DNA (gene)
--form new allele
--passed on
2) Recombination (crossing over)
--occurs during meiosis
--parents alleles
rearranged
Genetic
Variation
3) Hybridization is the crossing of
two different species.
--occurs when individuals can’t
find mate of own species
--topic of current scientific
research
Video:
https://www.youtube.com/watch?v=uXlHZGLzc6k
Key
Concept
Populations, not individuals evolve.
Natural selection acts on
distributions of traits.
--a normal distribution forms a bell
curve
--highest frequency near the mean
--frequencies decrease at extremes
--trait not undergoing natural
selection has a normal distribution
Natural
Selection
--can change the distribution of a
trait in one of three ways
Microevolution is evolution within a
population.
--observable change in allele
frequency
--can result from natural selection
1) Directional --selection that favors phenotypes
Selection
at one extreme
--ex) bacteria becoming resistant to
antibiotics
2) Stabilizing
Selection
--selection that favors phenotypes
the intermediate phenotype
--ex) two different predators prey
on the two extremes of a
population
3) Disruptive
Selection
Link:
http://www.open.edu/openl
earn/science-mathstechnology/science/migrati
on/content-section-3.3
--selection that favors both extreme
phenotypes
--ex) dominant adult males put
pressure on young males
in the bunting population;
rabbits (black, white, mix)
Key
Concept
Natural selection is not the only
mechanism through which
populations evolve.
Gene Flow
--movement of alleles between
populations
--occurs when individuals join a
population & reproduce
--keeps neighboring pop. similar
--increases the chance that pop. will
evolve into different species
bald eagle migration
Genetic
Drift
--is a change in allele frequencies
due to chance
--causes a loss of genetic diversity
--can be caused by a population
bottleneck
--occurs when an event drastically
reduces population size
--occurs after a bottleneck affect
Genetic
Drift
--the starting of a small population
can lead to genetic drift
--occurs when a few individuals start
a new population (founder effect)
--less likely to have individuals that
can adapt
--harmful alleles can become more
common due to chance
Video:
https://www.youtube.com/watch?v=mjQ_yN5znyk
Sexual
Selection
Sexual selection occurs due to
higher cost of reproduction for
females.
--males produce many sperm
continuously
--females are more
limited in potential
offspring each cycle
Sexual
Selection
There are two types of sexual
selection.
--intrasexual selection: competition
among males
--intersexual selection:
males display certain
traits to females
--Video:
https://www.youtube.com/watch?v=4j7GSu99LmY
Key
Concept
Hardy-Weinberg equilibrium
explains how populations evolve.
H-W Eq.
--describes populations that are not
evolving; is a type of model
--genotype freq. stay the same if:
1. Lg. population (no genetic drift)
2. No emigration/immigration (no gene
flow)
3. Random mating (no sexual selection)
4. No mutations (no new alleles)
5. No natural selection
H-W Eq.
--real populations rarely meet all
five conditions
--predicted genotypes are
compared with actual frequencies
--p2 + 2pq + q2 = 1
1) Genetic
Drift
--changes allele frequencies due to
chance alone
2) Gene
Flow
--moves alleles from one population
to another
3) Sexual
Selection
--selects for traits that improve
mating success
4) Mutation
--mutations produce the genetic
variation needed for evolution
5) Natural
Selection
--selects for traits that that are
advantageous for survival
Key
Concept
New species can arise when
populations are isolated (speciation).
Isolation
--when species are isolated there is
not gene flow
--isolated populations adapt to their
own environments
--genetic differences can build up
over generations
Reproductive
Isolation
--occurs between isolated pop.
--members of diff. pop. cannot mate
successfully
--final step to
becoming
separate
species
--two or more
species can
arise
Behavioral
Isolation
--behavioral barriers can cause
isolation
--includes differences in courtship
or mating behaviors
Behavioral
Isolation
--geographic barriers can cause
isolation
--physical barriers divide population
Video:
https://www.yout
ube.com/watch?v
=4j7GSu99LmY
https://www.youtub
e.com/watch?v=0D
1v4lY-1rw
--temporal barriers can cause
isolation
--timing of reproductive periods
prevents mating
Key
Concept
Evolution occurs in patterns.
--evolution through natural
selection is not random
--natural selection can have
direction
--the effects of natural selection
add up
over time
Convergent --convergent evolution: describes
v. Divergent evolution toward similar traits in
unrelated species (dolphin & sharks)
--one is a mammal
and one is a fish
--divergent evolution:
describes evolution toward different
traits in closely related species (ex.
Kit fox & red fox) come from
common ancestor and diverge
Coevolution --coevolution: two or more species
can evolve together
--evolutionary paths connect
--species evolve in response to
changes in each other
--can be beneficial or competitive
relationships (ants/acacia; crab/snail)
Extinction
--species can become extinct:
elimination of a species from Earth
--background extinctions occur
continuously at a very low rate
--occur at same rate as speciation
--usually affects a few species in a
small area
--caused by local changes in
environment
Mass
Extinction
--are rare but more intense
--destroy species at global level
--caused by catastrophic events
--at least 5 mass extinctions in last
600 million years
Punctuated
Equilibrium
Ancestral
species
may/may not
become
extinct.
--theory proposed by Eldredge &
Gould in 1972
--episodes of speciation occur
suddenly in geologic time
--followed by long periods of little
evolutionary change
--many species evolve from one
species in adaptive radiation
--ancestral species diversified into
many descendent species (branch)
Key
Concept
Specific environmental conditions
are necessary for fossils to form.
--permineralization occurs when
minerals carried by water are
deposited around a hard structure
--a natural cast forms when flowing
water removes all the original tissue,
leaving an impression
--trace fossils record the activity of
an organism
Fossil
Types
--amber preserved fossils are
organisms trapped in tree resin that
hardens after the tree is buried
--preserved remains form when an
entire organism becomes in
materials such as ice
--specific conditions are needed for
fossilization
--only a tiny percentage of living
things become fossils
Relative
Dating
--used to estimate the time when an
organism lived by comparing the
placement of its fossils to the
placement of other organisms
--compares fossil placement in rock
layers
Radiometric
Dating
--provides a more accurate way to
estimate the age of fossils
--uses isotopes of unstable elements
--the half-life is the amount
of time of the isotope to decay
--U-238 is used to date rock
--C-14 used to date organisms
--C-14’s half- life
is too short to
date rock
Radiometric Video:
Dating
https://www.youtube.com/watch?v=
1920gi3swe4
Video:
Key
Concept
The geologic time scale divides
Earth’s history based on major past
events.
--index fossils are a tool to
determine the relative age of rock
layers
--existed only during specific spans
of time
--include fusulinids and trilobites
Geologic
Time Scale
The geologic time organizes Earth’s
history
--history of Earth is represented in
the geologic
time scale
Dinosaurs reached
their peak and
became extinct at the
end of the Cretaceous
Period
Geologic
Time Scale
Eras last tens to hundreds of millions
of years (two or more periods)
--three eras: Cenozoic, Mesozoic,
Paleozoic
All existing animal
phyla developed
during a short period
of time known as the
Cambrian Explosion.
Geologic
Time Scale
Periods last tens of millions of years
--most commonly used unit
--associated with rock systems
Epochs last several million years.
--mass extinctions
helped scientists
determine where
one period ends
and another
begins