Transcript 5.4 Evolution - Walnut High School

5.4
Evolution
5.4.1 Define evolution
 cumulative change in the heritable
characteristics of a population.
• ‘heritable’ –
• changes must be passed on genetically from one
generation to the next
• implies that evolution doesn’t happen overnight
• ‘cumulative’ • one change isn’t enough to have major impact on
the species
• ‘population’ • changes do not affect just one individual
5.4.2 Outline evidence for evolution.
 Fossil record
 transition species
 Comparative Anatomy
 homologous & vestigial structures
 Comparative Embryology
• embryonic development
 Molecular record
 protein & DNA sequence
 Artificial selection
 human-caused evolution
Fossil record
 Layers of sedimentary rock contain fossils
 new layers cover older ones, creating a record
over time
 fossils within layers show that a succession of
organisms have populated Earth throughout a
long period of time
Fossil record
 A record showing us that today’s organisms
descended from ancestral species
550
500
Body size (kg)
450
Equus
400
350
300
250
Merychippus
200
Mesohippus
Hyracotherium
150
100
50
Nannippus
60
55 50
45 40
35
30 25 20 15 10
Millions of years ago
5
0
Fossil record
 A record showing us that today’s organisms
descended from ancestral species
Comparative Anatomy
 Homologous structures
 Similar structure
 Similar development
 Different functions
 Evidence of close evolutionary
relationship
 recent common ancestor
Comparative Anatomy
 Homologous structures
 similarities in characteristics resulting from
common ancestry
 Results of adaptive radiation - emergence of many
species from common ancestor
 All vertebrates have similar bone structures in their
limbs
Comparative Anatomy
 Analogous structures
 Separate evolution of structures
similar functions
 similar external form
 different internal structure & development
 different origin
 no evolutionary relationship

Don’t be fooled
by their looks!
Comparative Anatomy
 Analogous structures
 Flight evolved in 3 separate animal groups
 evolved similar “solution” to similar “problems”
 may have developed as a result of convergent
evolution – unrelated species share the same
environment (similar environmental pressures) and
independently evolve similar structures
Comparative Anatomy
Analogous structures
 Fish: aquatic vertebrates
 Dolphins: aquatic mammals


similar adaptations to
life in the sea
not closely related
Those fins & tails
& sleek bodies are
analogous structures!
Comparative Anatomy
 Homologous structures
 Analogous structures
 Results from:
 Results from:
 Adaptive radiation
 Convergent evolution
 Common ancestor
 Different ancestors
 Similar origin
 Different origin
 Different functions
 Similar functions
 Ex. wing of bat, human
 Ex. wings of bird, wings of
arm, dolphin flipper
insect
Remember:
Adaptive
radiation
Convergent
evolution
Comparative Anatomy
 Vestigial structures
 Modern animals may have structures that serve little or
no function
 remnants of structures that were functional in
ancestral species
 deleterious mutations accumulate in genes for noncritical structures without reducing fitness
 snakes & whales — remains of pelvis & leg bones of
walking ancestors
 eyes on blind cave fish
 human tail bone, appendix
Comparative Anatomy
 Vestigial structures
PBS: Whales in the Making
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
Comparative embryology
 Similar embryological development in closely related
species
 all vertebrate embryos have similar structures at different
stages of development

gill pouch in fish, frog, snake, birds, human, etc.
Molecular record
 DNA & proteins are a molecular record of
evolutionary relationships
 Closely related species have sequences that are
more similar than distantly related species
Human/kangaroo
100
Human/
cow
Dog/
cow
Nucleotide substitutions
75
Rabbit/
rodent
Human/rodent
Llama/
cow
Horse/
donkey
50
Horse/cow
Sheep/
goat
Pig/
cow
25
Goat/cow
0
0
25
50
75
Millions of years ago
100
125
Molecular record
Human Macaque
Dog Bird
Frog
Lamprey
32 45
67
125
20 30 40 50 60 70 80 90 100 110 120
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans
Artificial selection (selective breeding)
 Artificial breeding can use variations in populations
to create vastly different “breeds” & “varieties”
 line of evidence that supports evolution by natural
selection
 the breeding of domestic plants and animals to produce
specific desirable traits (ex. different breeds of dogs)
 people are doing the “selecting” rather than the
environment
5.4.3 State that populations tend to produce more
offspring than the environment can support.
Natural populations (a population consists of
all the individuals of one species in a particular
area) of all organisms have the potential to
increase rapidly – organisms produce far more
offspring than can possibly survive
5.4.3 State that populations tend to produce more
offspring than the environment can support.
 More than needed to keep species around
 More than K (carrying capacity) can support, but
limited resources
 Intraspecific competition
 Some have competitive advantage such as traits,
behaviors, symbiosis)
 More fit (competing for resources,
fighting disease, etc.) = More likely
to successfully reproduce
 Freq of these alleles higher in next
generation
5.4.4 Explain that the consequence of the potential
overproduction of offspring is a struggle for survival.
5.4.4 Explain that the consequence of the potential
overproduction of offspring is a struggle for survival.
• Some individuals selected FOR
• Some selected AGAINST
• Survivors (selected FOR) form new breeding
population
• Increases freq of advantageous alleles
5.4.5 State that the members of a species
show variation.
Individual members of a population differ from one
another in their ability to obtain resources, withstand
environmental extremes, escape predators etc.
(Variation)
5.4.5 State that the members of a species
show variation.
 At least some of the variation among individuals in
traits that affect survival and reproduction is due to
genetic differences that can be passed on from
parent to offspring – natural selection
 Over many generations, differential, or unequal,
reproduction among individuals with different
genetic makeup changes the overall genetic
composition of the population – evolution
 Evolution is the result of natural selection
5.4.6 Explain how sexual reproduction promotes
variation in a species.
5.4.6 Explain how sexual reproduction promotes
variation in a species.
 MIXING IT UP w/MEIOSIS!
 Random assortment of chromosomes in Metaphase I
 2^n combinations of chroms in daughter cells
 8,388,608 in humans!!
 Crossing-over in
Prophase I
 New combos of alleles
on a chromosomes
 Random fertilization 
any gamete can fertilize any
gamete from the other individual
5.4.7 Explain how natural selection leads to evolution.
Darwin’s Theory of Natural Selection:
1. Populations produce more offspring than can
2.
3.
4.
5.
possibly survive. (overproduction)
Individuals in a population vary extensively from
each other, mostly due to inheritance. (variation)
Struggle to survive: individuals whose inherited
characteristics best fit to environment leave more
offspring than less fit. (survival of the fittest)
Unequal ability of individuals to survive and
reproduce leads to gradual change in population.
(adaptation)
Favorable characteristics accumulate over
generations – (descent with modification).
5.4.7 Explain how natural selection leads to evolution.
 Individuals with genetic characteristics that are WELL-
adapted for environment
 Tend to be MORE successful at accessing resources
 And thus have BETTER chance of surviving to
maturity
 Since they survive to adulthood, these successful
organisms have a better chance to reproduce and
pass on their genetic characteristics to the next
generation.
 Over many generations, accumulation of changes
in the heritable characteristics of a population
results in evolution. THE GENE POOL HAS
CHANGED!
5.4.8 Explain 2 examples of evolution in response to
environmental change. (one must be antibiotic
resistance in bacteria)
5.4.8 Explain 2 examples of evolution in response to
environmental change. (one must be antibiotic
resistance in bacteria)
http://www.sumanasinc.com/scienceinfocus/sif_antibiotics.html
5.4.8 Explain 2 examples of evolution in response to
environmental change – peppered moth melanism
5.4.8 Explain 2 examples of evolution in response to
environmental change – peppered moth melanism
5.4.8 Explain 2 examples of evolution in response to
environmental change – insecticide resistance
Insecticide Resistance
– evolution in action
 Insecticide &
drug resistance
 insecticide didn’t
kill all individuals
 resistant survivors reproduce
 resistance is inherited
 insecticide becomes less & less
effective