KAUPAPA
What is the evidence for
evolution?
How do analogous and
homologous structures
exemplify commonality and
diversity?
ADAPTATION
humpback whale
Megaptera novaeangliae
breathe air
give birth to live young
suckle - produce milk
early relatives of whales lived
on land
ADAPTATION
genetic similarities between
present day whales and hippos
closest living relatives
transition from land to water
those better adapted for living in
water survived
PAKICETUS
ancient relative of the present
day whales
typical land animals, with
aquatic adaptations
limbs with five digits adapted for
walking on land and wading in
streams
AMBULOCETUS
more aquatic lifestyle
shorter legs with paddle-like hands
and feet
millions of years
forelimbs evolved into flippers of the
present day whales
CHECKPOINT 1
DARWIN OBSERVES
more offspring produced than can be
supported
competition for natural resources
food and water, space
population size remains fairly constant
carrying capacity
individuals within a population are not identical
but exhibit variations in their characteristics
DARWIN OBSERVES
variations that help individuals adapt
better to the environment are more
likely to survive
reproduction passes on the positive
variations
less favourable variations are less
likely to survive
natural selection
DARWIN OBSERVES
over many generations,
natural selection leads to
populations adapted for
specific environments
barriers to reproduction
or reproductive isolation
may lead to the formation
of a new species
LAMARCK PROPOSES
physical changes acquired by organisms during
their lifetime were passed on to their offspring
1. change in the environment led to the use of
certain organs and disuse of others among
organisms.
2. organs that were used more would increase in
size over the lifetime of the organisms and
inversely true
3. these changes acquired over the lifetime of an
individual would be passed onto the offspring
LAMARCK PROPOSES
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CHECKPOINT 1
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CHECKPOINT 2
EVIDENCE OF EVOLUTION?
CHECKPOINT 2
DNA
what is it?
how does it work?
why is it important?
DNA
coding for protein synthesis
stored in chromosomes
located in the nucleus of a cell
CLOSE COUSINS
how similar are we?
98.8% of our DNA is identical
CLOSE COUSINS
how similar are we?
60% of our DNA is identical
DNA
MOLECULAR PHYLOGENY
comparative analysis of the sequences of
the bases in DNA and RNA
sequences code for amino acids
analysis of amino acids in proteins
determine how closely two species are
related to each other at a molecular level
similarity in genes and proteins indicates
more closely related species
MUTATIONS
changes in the genome are due to mutations
rate of mutation of a gene is fairly constant
differences accumulate over time
forms the basis of the molecular clock
species with fewer differences in their genomes
(and amino acids) would have recently split or
diverged from each other
AMINO ACID SEQUENCES
SELECTIVE
BREEDING
all dog breeds can trace their
ancestry to an extinct wolf species
humans creation of these breeds
dogs have been bred for their
desired characteristics
evidence of evolution by natural
selection?
SELECTIVE BREEDING
natural selection
organisms better adapted to the
environment survive, reproduce and pass
on the traits to their offspring
selective breeding
humans decide the favourable variations
over generations, humans continually select
organisms with desirable characteristics,
removing those with less desirable traits, leading
to a rapid genetic change in the population
SELECTIVE BREEDING
cows to increase the milk
production
hens to increase egg size
crops to increase disease
resistance and yield
SELECTIVE BREEDING
SELECTIVE BREEDING
WILD MUSTARD PLANT
Brassica oleracea
broccoli (flower buds/stems)
cauliflower (flower buds)
cabbage (terminal leaf bud)
kale (leaves)
ARTIFICIAL SELECTION
DARWIN AGAIN
Darwin’s pigeon breeding
experiments helped him
frame his theory of natural
selection
he noted that the breeds, while
morphologically distinct from each
other, were descendants of the wild
rock pigeon that evolved over years
of selective breeding
DARWIN AGAIN
parallels between
- selective breeding due to human
intervention
- natural selection by the environment
“while selective breeding was a more rapid
process, in both cases, selection of
favourable characteristics over generations,
led to evolution”
HOMOLOGOUS STRUCTURES
vertebrates
human, whale, bat, cat, lizard
limbs that look different and carry out
different functions
yet have the same basic bone
structure
how is this evidence?
HOMOLOGOUS STRUCTURES
arrangements of bones
in the pentadactyl
vertebrate limbs of
different mammals
similarity in their structures
and arrangements of the
humerus, radius, ulna,
carpals and digits
DIVERGENT EVOLUTION
organisms arising from the
same ancestral species adapt
to different environmental
conditions
pressures of natural selection
homologous structures (or
organs) act as evidence for
evolution as they indicate a
common evolutionary organ
DIVERGENT EVOLUTION
ANALOGOUS STRUCTURES
body parts that have the same
or similar function in different
groups of organisms but have
different structures
convergent evolution
distantly related groups of organisms
face similar environmental conditions
and adapt in similar ways
ANALOGOUS STRUCTURES
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CHECKPOINT 2
CHECKPOINT 3
SPECIES
what is a species?
when do we declare a
new species has evolved?
SPECIES
similar organisms that can mate with
each other and produce viable, fertile
offspring
reproductive compatibility
defines a species
true for most plants, animals and fungi
SPECIES
Polar bears and Alaskan brown bears have
always been considered as two separate species
1936 at the U.S. National Zoo, a male polar bear
accidentally got into an enclosure with a female
Alaskan brown bear
three offspring were the result and these
offspring were able to breed successfully
how does this challenge our understanding of
species?
SPECIES
approximately 8.7 million
eukaryotic species on Earth
speciation
the process by which new
species arise
splitting of one ancestral species
into two or more descendent
species which are genetically
different from each other and
can no longer interbreed
GENE POOL a population of species shares a
gene pool or a collection of the
variants of the genes in the species
modification of the original gene
pool into separate gene pools in a
way that interbreeding is prevented
genetic separation
speciation increases the total
number of species on Earth
extinction of species reduces the
total number of species on Earth
REPRODUCTIVE ISOLATION
one of the drivers for speciation
reproductive isolation due to geographical
barriers such as:
- physical barriers like mountain ranges or
river
- large distances between populations
- human-made barriers like large roads or
dams
prevent populations of the same species from
interbreeding and/or producing fertile offspring
REPRODUCTIVE ISOLATION
1. a large population of individuals occupies a
habitat
REPRODUCTIVE ISOLATION
1. a large population of individuals occupies a
habitat
2. the formation of a new geographical barrier
divides the original population into two
smaller populations, the geographical barrier
prevents members of the two populations
from mixing and interbreeding
REPRODUCTIVE ISOLATION
1. a large population of individuals occupies a
habitat
2. the formation of a new geographical barrier
divides the original population into two
smaller populations, the geographical barrier
prevents members of the two populations
from mixing and interbreeding
3. in different environments, evolutionary
forces such as natural selection, mutation
and genetic drift act independently on the
gene pools of the two populations for many
generations
DIFFERENTIAL SELECTION
genes that provide better adaptation to environmental
challenges are selected over others and transmitted
through generations
natural selection leads to differential reproduction and
in a way differential selection
eventually leads to genetic separation
the resulting behavioural and/or physiological changes
prevent the populations from mating
CASE STUDY
chimpanzees
larger, more aggressive and live in
male-dominated groups.
bonobos
more slender, more playful and
have female-dominated groups
CASE STUDY
chimpanzees Pan troglodytes
bonobos Pan paniscus
African apes that live in close
proximity with each other
chimpanzees are distributed
across equatorial Africa
bonobos are restricted to a region
south of the Congo River
CASE STUDY
common ancestral species living in the
rainforests of the Democratic Republic of the
Congo
formation of the Congo River, the deepest
river in the world, nearly 1.5 to 2 million
years ago
divided the ancestral population into two
groups
CASE STUDY
the group north of the river faced intense
competition for resources
intraspecific competition
with each other
interspecific competition
with the ancestral population of gorillas.
Aggressive tendencies were evolutionarily
selected. Over time, this group evolved to
the present day chimpanzees.
CASE STUDY
to the south of the Congo River
resources were plentiful, the apes evolved
to become slender and more cooperative,
eventually giving rise to the bonobos
development of a geographical barrier and
differential selection over the course of
time led to reproductive isolation
leads to speciation
CASE
STUDY
CASE
STUDY
2
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identify which species is most
closely related to the Asian
elephant
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CHECKPOINT 3
CHECKPOINT 4
Kaibab squirrels
Sciurus aberti kaibabensis
Abert squirrels
Sciurus aberti
SPECIATION
speciation is the
formation of two or more
species from an ancestral
species
allopatric speciation
sympatric speciation
ALLOPATRIC
allopatric speciation is geographical isolation
1. a population of a species is split into two by a geographical
barrier
2. prevents exchange of genetic material - isolated
3. experience differential selection and diverge genetically
4. reproductive isolation - speciation
ALLOPATRIC
ancestors of the Abert squirrels
had a wide distribution
thousands of years ago, when
the Grand Canyon formed, a
small population of squirrels got
cut off from the main
population
SYMPATRIC
new species is formed within the same
location due to isolating mechanisms
- behavioural isolation
- temporal isolation
CASE STUDY
Apple maggot flies
ancestors of these fed and laid their
eggs on hawthorns (a plant native to
North America)
apples introduce to America
used by the flies as food sources,
laid their eggs on them
CASE STUDY
reproduction is fruit specific
apple flies mate with other apple flies
hawthorn flies with other hawthorn flies
intraspecific breeding
mating within the species
two groups with limited gene flow
after 200 years, selection pressure has led to
two genetically divergent groups
TEMPORAL ISOLATION
differences in the timing of the reproductive cycle
(mating seasons or gamete production)
prevents interbreeding even though the species
may share the same geographical location
two species of cicadas in the USA
Magicicada tredecim sexual maturity in 13 years
Magicicada spetendecim, sexual maturity in 17 years
once in 221 (13 × 17) year cross over
BEHAVIOURAL ISOLATION
mating rituals
courtship dances or mating calls to attract other
members of the same species
organisms of the same species may develop different
mating rituals over a period of time
behavioural isolation can occur when these rituals vary
and the individuals do not interbreed
over generations, this could lead to reproductive
isolation and speciation
BEHAVIOURAL ISOLATION
BEHAVIOURAL
SEPARATION
TEMPORAL SEPARATION
REPRODUCTIVE ISOLATION
prezygotic barriers
barriers that prevent the formation of the zygote
postzygotic barriers
barriers that occur after the zygote is formed
SPECIATION
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CHECKPOINT 4
ADAPTIVE RADIATION
rapid evolution of an ancestral species
in different lines to utilise the available
ecological niches
Darwin’s finches on the Galapagos Islands
ancestral finch species that arrived on the
islands were seed-eating birds with a
short, thick beak
ADAPTIVE RADIATION
uninhabited islands provided unlimited
food resources
insects, fruits, buds, seeds and grubs
variations in the beaks resulted in diverse
sources of food
selection of favourable beak variations led
to a rapid diversification of the finches into
diverse ecological niches
ADAPTIVE RADIATION
ADAPTIVE RADIATION
marsupials of Australia
that have diversified from a central
ancestral stock to occupy different
habitats
approximately 200 species of marsupials
despite being closely related, the species
can coexist without competing for
resources
ADAPTIVE RADIATION
Hawaiian silversword
ancestors of these plants arrived on
the island of Kauai from western North
America
adaptation to different ecosystems led
to rapid diversification
adaptive radiation leads to
biodiversity
HYBRIDISATION
interbreeding between two different
species that leads to a new species
this new species is often
reproductively isolated from the
parent species
horse + donkey = mule
HYBRID PREVENTION
prezygotic barriers
- variation in the courtship behaviour
- behavioural isolation
postzygotic barriers
- reduce the viability of the zygote
- reduce the viability of the young one and the
adult
- decrease the fertility of the hybrid and its
offspring
HYBRIDISATION
horse + donkey = mule
donkey has 62 chromosomes
horse has 64 chromosomes
mule has 63 chromosomes
does not have the required pairs of
homologous chromosomes and so is
infertile
PLANT HYBRIDISATION
some fruits and vegetables we consume are
hybrids
some barriers to hybridisation still exist
pollen-pistil incompatibility
most varieties of common wheat rarely form seeds
when pollinated with pollen from rye plants
hybrid watermelons are seedless and
unable to produce offspring
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CHROMOSOME SETS
haploid
single set of chromosomes
diploid
two sets of chromosomes (humans)
triploid
three sets of chromosomes
polyploidy
cell or organism acquires one or more
additional sets of chromosomes
POLYPLOIDY
a rapid and relatively simple form
of speciation
caused due to nondisjunction of
chromosomes during mitosis or
meiosis
formation of gametes with
additional sets of chromosomes.
ALLOPOLYPLOIDY
an allopolyploid is a hybrid
multiple chromosome sets that
are derived from different
parental species
polyploid offspring are often
more vigorous and resistant to
disease than the parent species
ALLOPOLYPLOIDY
normal gamete (species 1) combines with
the polyploid gamete (species 2)
resulting cell is sterile due to the
abnormal number of chromosomes
if mated with normal gamete, viable
offspring can be produced
if the offspring are unable to interbreed with the
parental species however can mate with each
other, this would result in speciation
ALLOPOLYPLOIDY
tobacco, wheat, Knotweed, kiwifruit
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