Download Ch 15 Natural Selection and Evolution Evidence

Chapter 15:
Natural Selection and
the Evidence for Evolution
A unit addressing evolution, its
mechanisms and outcomes.
Do You Remember??
Fossils Shape Ideas
1. How are fossils formed?
2. Why are some fossil species
extinct?
3. What kinds of relationships
exist between fossil species
and modern species?
Natural Selection:
A Mechanism for change
in populations
Darwin theorized: Organisms with
certain “favorable” variations survive,
reproduce, and pass those variations
onto the next generation.
Natural Selection
An example explaining Darwin’s natural
selection proposition:
Over Time
Only individuals with useful
variations, such as speed,
speed
survive & reproduce
Evidence for Evolution
• Structural adaptations
arise over time and helps
promote survival of the
organism
– environmental changes:
blind mole rat
– mimicry: fly that
resembles wasp
– camouflage: walking
stick insect
Physiological Adaptations
• changes in organism’s
metabolic processes
• can evolve rapidly
• example: antibiotic
resistance in bacteria
Bacilli bacteria
Other Evidence for Evolution
• Fossils:
Via the analysis of:
-footprints
- petrified remains
- casts
- imprints
- amber and ice preservation,
Scientists can make distinct
correlations between ancient
organisms and modern day
species
• Anatomy
– homologous structures:
structural features with a
common evolutionary
origin
-homologous structures
can be similar in
arrangement, function, or
both!
Analogous Structures:
Structural features that
do not have a common
evolutionary origin, but are
similar in function
Example: bird wings and
butterfly wings
Vestigial Structures:
body structure that has no
function in the present day
organism but was probably
useful in its ancestor
whale
Embryology:
similarities in
development of
embryos suggests
a distant,
common ancestor
A Fish, Reptile, Bird, & Mammal
Biochemistry:
using DNA and protein
sequence similarities, it reveals
information about relationships
between individuals and species
*** In Summary, Scientists use data from:
Fossils
Anatomy
Embryology
& Biochemistry
To interpret the evolutionary relationships
among species.
Hmmm. I must
consider a variety
of facts when
analyzing the past
*End 15.1 here
Mechanisms of Evolution
•POPULATIONS
EVOLVE!
•Individuals don’t
Question: If a population is in Genetic
Equilibrium, is it evolving? Answer:
NO!
Terms:
– gene pool: all of a population’s genes
– allele frequency: % of any allele in gene
pool
– genetic equilibrium: frequency of
alleles remains the same over
generations
Changes in Genetic Equilibrium
Mutation: change in gene sequence
which alters protein and expression
Other causes for changes in genetic
equilibrium:
1.
environmental factors
2.
chance
3.
genetic drift
4.
gene flow
Genetic Drift
• alteration of allelic frequencies by
chance events
• can greatly affect small populations
– Example: Fingers in Amish population
Gene Flow
* migrating individuals entering
and leaving a population
Hello!
Bu-Bye!
Natural Selection
• Selection of variations in organisms
which enhance their survival
• There are 3 types of Natural
Selection that act on variation:
– Stabilizing
– Directional
– Disruptive
Natural Selection, con’t
Stabilizing Selection:
favors average individuals/reduces variation
in a population
example: In a spider population, large spiders
are seen and eaten, small spiders can’t
compete for food, so it’s the average sized
spider that is selected for.
• Directional Selection
– occurs when natural selection favors one of the
extreme variations of a trait
– example:
if a woodpecker’s insect species
food supply burrows deeper into the bark, then
there will be selection of longer beaks over
shorter beaks and average beaks.
• Disruptive Selection
– When individuals of either extreme of a trait’s
variation are selected for
– Can lead to the evolution of 2 new species
– In an environment of light and dark colored
rocks, the limpet marine organisms which are
white and living on light rock survive while
those that are dark living on dark rocks also
survive. Those of intermediate color can be
seen on both backgrounds and are eaten.
Speciation
• Definition: the evolution of
new species
• A possible cause:
– Geographic isolation
When a physical barrier
divides the population
Example: mountain
range or body of
water dividing a
population
Reproductive Isolation:
Occurs when formerly interbreeding
organisms can no longer mate & produce
fertile offspring
•Two examples:
•Genetic material changes
example: California salamanders
•Behavior changes
example: Tree frogs mating in
different seasons
Reproductive Isolation, con’t:
Change in chromosome
numbers
•example: donkey (64) and
horse (62) create mule
(63) which is sterile
•Polyploid species: an
individual having a multiple of
the normal set of
chromosomes
•example: crop plants like
wheat
mule