Download Evolution - Year 10 Life Science

EVOLUTION
Year 10 Life Science
EVOLUTION
Evolution is the gradual development of
different species from a common ancestor
over time
NATURAL SELECTION
A species gradually becomes better
Adapted to its environment
HOMOLOGOUS STRUCTURE
similar structure
and provide
evidence of an
evolutionary
relationship
HOMOLOGOUS STRUCTURE
Homologous structures are features of organisms that have a similar structure and
provide evidence of an evolutionary relationship
Similar structure, closely related, different function
E.g. wing of bird, wing of bat, leg of lizard, flipper of whale, arm of human all
have same basic structure
 Pentadactyl limb (having 5 digits)
 However, in each organism is has been modified to suit a different way of
life.
ANALOGOUS STRUCTURES
These structures
may have come
about, due to the
environment in
which they live in.
ANALOGOUS STRUCTURES
Analogous characteristics are those that look similar but are genetically
very different. (no evolutionary relationship)
Similar Structure. Not Related. Same environment
These structures may have come about, due to the environment in
which they live in.
 Eg. sharks and dolphins seem similar in appearance however genetically these animals
are completely different.
 Both need flippers, to be able to swim in the water.
 A butterfly and a Bird are completely different species, but both have the similar
structure of ‘wings’ to enable them to fly
DIVERGENT EVOLUTION
oDivergent evolution: formation of new species due to
change in environment
oWhen two or more species evolve from a common
ancestor
Example: Finches on the Galapagos Islands
o Evolved into different species to eat different foods
CONVERGENT EVOLUTION
o Where two organisms have similar analogous structures but different ancestors (not related)
o When two or more unrelated species adopt similar adaptations in response to common
environmental conditions
Example: Sharks and dolphins are similar in appearance but are not related
LAMARCK'S THEORY
o According to Lamarck’s theory, organisms will evolve over time
based on the repeated use of body structures.
o Evolution by inheritance of acquired characteristics
In this example, the Ancestral form consumed plant material and needed extra height
to reach the higher branches. Over time, the animal evolved because of constant use
of neck muscles and leg muscles to reach higher branches.
Lamarck's
Theory
Giraffe's
inherited long
necks from short
necked
ancestors
who continually
stretched their
necks to reach
food
Darwin proposed that variation was critical in
understanding how species change over long
periods of time. His argument was that selection
can not occur without differences in a
population (variation)
Darwin’s
Theory
Long necked
and short
necked giraffes
once existed
together
but the longnecked giraffe
had an
adaptive
advantage
EXPLAIN HOW THE EVOLUTION SHOWN IN THE DIAGRAM BELOW
WOULD HAVE OCCURRED ACCORDING TO LAMARCK’S THEORY.
ANSWER
oThe ancestral organism stretched its legs to reach the higher
branches.
oThis ‘stretched leg’ characteristic (an acquired characteristic) was
inherited by the offspring.
oThese offspring in turn stretched further and then passed on their
‘stretched leg’ characteristic to their offspring.
oThe long-legged form shown eventuated from this stretching and
inheritance.
SPECIATION
o The theory of evolution by natural
selection proposes that all species are
related.
o Some species more closely related than
others, but ultimately all life should be
able to be traced back to one original
species.
A change in species is
usually due to some
form of isolation from
an original population
SPECIATION
Speciation is the process by which one species
splits into two or more separate species.
The process of speciation occurs in three steps:
 Variation: There must be variation in the population
 Isolation: This means that different groups must be prevented from interbreeding,
this stops any differences from one population reaching the other population
 Selection: Natural selection affects the genotype and causes changes (mutations)
that prevent the groups breeding even if they got back together.
SPECIATION
EXAMPLE
QUESTIONS
1. Describe two ways in which a population may become geographically isolated to form two
populations?
Ocean, river, mountains, earthquake, sand blocking an estuary, desert/dry conditions, gorge
2. Suggest two reasons why the two separated populations may evolve differently
Different mutations occur in each population. Differences in conditions would mean that
different characteristics are ‘selected for’ in each population
QUESTIONS
3. The group of flightless birds, known as ratites, occur in Australia (emu), New
Zealand (kiwi), South America (rhea), Pupua New Guinea (cassowary) and Africa
(ostrich). How can the distribution of these related species be explained?
The ancestral ratite lived on Gondwana (one land mass). When this split to form the
continents, the ratites on each continent evolved in isolation, giving rise to the
different forms/new species.
ARTIFICIAL SELECTION VS NATURAL SELECTION
Artificial selection is the process by which humans deliberately choose to
breed particular organisms with desirable features.
Eg. domesticated dogs, different breeds of dogs are
all one species and different breeds produced by
Artificial selection.
Natural Selection is the process by which the
environment acts on the population
HUMAN EVOLUTION
The name of our species “homo sapiens” means the “wise man.”
According to fossils we have been around for about 200,000 years.
Fossils indicate other human-like species have existed too.
PRIMATES, HOMINIDS AND HOMININS
Primates include lemurs, monkeys, apes, gibbons and
humans.
 To be classified in this species the organism must have
“grasping hands, nails rather than claws and forward
facing eyes”
Hominids include apes, chimps and humans. (no tail)
Hominins are humans and their common ancestors. There
are key differences which show how different Humans now
are from their original primate ancestors.
HOW STRUCTURES HAVE CHANGED….
Humans are now a ‘sub-tribe’ as they have the ability to walk on
2 legs (known as bipedalism)
 Differences between primates and humans include:
 Skull
 Size
 Jaw shortens
 location of foramen magnum
 Vertebral Column (S Shaped)
 Pelvis (wider)
 Femur (angled inwards)
 Feet (flat)
SUMMARY/KEYWORDS
Pentadactyl limb  having 5 digits
Homologous structure  Features of
organisms that have a similar structure
and provide evidence of an evolutionary relationship (common ancestor).
Do not have to have the same function in all species.
Analogous structure  Similar Structure. Not Related. These structures may have come about,
due to the environment in which they live in.
Divergent Evolution  When two or more species evolve from a common ancestor
Convergent Evolution  When two or more unrelated species adopt similar adaptations in
response to common environmental conditions
SUMMARY/KEYWORDS
Artificial selection humans deliberately choose which individuals will mate
Natural selection the environment acts on the population
Darwin’s theory selection cannot occur without differences in a population
Lamarck’s theory Evolution by inheritance of acquired traits
Genetic isolation keeping potentially interbreeding groups apart by some barrier
Evolution  the gradual development of different species from a common ancestor