Transcript Variation and Evolution

Variation and Evolution
What is Variation?
• In any population of living things there will be
slight differences or variation between
individuals in the population.
• For example differences in size, colour,
behaviour etc .
What do these differences mean?
Variation means that some individuals in a
population will be better suited to the
environment than others. This may mean that
these individuals are better camouflaged and
therefore less likely to be eaten by predators.
So…
The individuals that are
better suited to the
environment will survive
longer and therefore be
able to mate and pass
their successful variations
on to the next generation.
For example, after a long
period of time there
would be larger numbers
of the dark moth.
We would then say…
That the population has evolved
which means that it has changed
over time.
Where did this idea come from?
The idea that populations of plants and animals
change over time to better suit their environment
was first proposed by Charles Darwin in 1850’s.
• From a young age Darwin was passionate about
science and nature. He collected lots of different
things like stones and beetles and performed
experiments with his brother in the garden shed.
• From 1831 – 1836 he voyaged around the world
as a naturalist on The Beagle, collecting and
making detailed observations of many different
species of plants and animals.
• He published a book On the Origin of Species in
1859 and was ridiculed for his ideas because they
opposed the teachings of the church at that time.
• Today Darwin’s idea that species have
changed over time to better suit their
environment has gained acceptance as a
scientific theory.
• It is called Natural Selection.
• Natural Selection is sometimes called
‘survival of the fittest’. How does it work?
http://www.youtube.com/watch?v=0SCjhI86grU (What is natural selection –
stated clearly)
Natural selection
Variation
Individuals show variation:
some variations are more
favorable than others
Overproduction
Populations produce too
many offspring, many will
die
Natural Selection
Individuals that are best
suited to the environment at
the time will survive and
reproduce
Inheritance
Variations are inherited. The best suited individuals
will leave more offspring, passing on their successful
variations to the next generation.
Darwin’s Theory of
Evolution by
Natural Selection.
Modelling Natural Selection
In your pair you will receive a pile of paper discs
which represent different coloured moths.
Count out 20 of each phenotype (white, black
and speckled). Person 1 scatter them over the
sheet of newspaper while the other person is
not watching. Person 2 (represents a bird) uses
forceps (their beak) to pick up as many moths as
they can in 20 seconds (Person 1 times).
Swap roles and repeat.
Questions
• How many butterflies of each phenotype did you
catch?
• How many of each phenotype did the whole class
catch?
• The population contained 20 white, 20 black and
20 speckled butterflies. Which ones were the
best at avoiding predation (being eaten by the
bird)? Why were they more successful?
• What is likely to happen to the proportions of
each phenotype in the next generation? Why will
this happen?
But what about us?
• When Darwin told the world about his discovery in his book
On the Origin of Species he didn’t really say anything about
humans other than to hint his ideas would reveal the secrets
of human history. But the message was clear; natural
selection is the process which has shaped all species,
including us!
• Other scientists wrote books about human evolution, often
comparing our bones to those of apes and monkeys.
Eventually Darwin decided to write a book about it too to set
the record straight about what the thought about humans. He
wrote a book called The Descent of Man. He presented lots of
evidence to support the theory that humans evolved from
apes. He also argued that all the different human races were
one species, which was a keenly debated subject in Victorian
times.
An adaptation is a special change to a species that helps
the organism survive in its environment. There are three
types of adaptations:
Structural: A body part you can see such as wings on a
bird to enable it to fly.
Functional: The organism’s body is able to perform a
function or do something that most organisms can’t. Eg,
a snakes ability to produce poison or a deep sea fish’s
ability to produce anti-freeze.
Behavioural: An instinctive behaviour that the entire
species carries out, eg penguins huddling for warmth or
bears hibernating for winter.
What is Evolution?
• http://www.youtube.com/watch?v=faRlF
sYmkeY (Simpson’s evolution)
• Evolution is the gradual change in species
over time.
• Evolution happens because the environment
is continually changing.
• Evolution occurs by Natural Selection.
http://www.youtube.com/watch?v=GhHOjC4oxh8 (What is evolution – stated clearly)
Our planet is in a state of change.
• All the pollution that we
produce with our cars,
power plants and
aeroplanes is changing
our climate. At the same
time, we’re cutting down
lots of forests and moving
animals and plants from
one part of the world to
another. This is causing
chaos in the natural
world!
Climate change is
a big issue;
Temperatures are predicted to rise rapidly over the next
hundred years. This might sound quite nice but it will have
lots of bad effects. Sea levels will rise and all the different
weather systems will change. Lots of animals and plants are
now found where they weren’t before. Their presence is
causing lots of problems for local wildlife – they’re messing up
all the food webs!
The UK has lots of new species which have either been
accidently introduced or are taking advantage of the warming
weather: cannibalistic ladybirds, rampant crayfish and exotic
spiders to name a few!
And
•
The changing weather has also confused
many birds which migrate. They rely on
clues from the weather to time their migrations.
Because the temperature is changing so quickly they’re
starting to get it wrong and they can leave too early
and arrive at their destination when there’s no food, or
leave too late and face the
same problem!
Rainforests
• In many tropical regions
people are cutting down the
rainforests to use the trees
as timber, or to make the
land good for farming.
Unfortunately half the
world's species live in the
rainforest! Their habitats
are being destroyed or cut
up into chunks, isolating
small groups from each
other and making them
more vulnerable
Forests in Brazil have been cut down to
make way for crops such as soya
So
We have to tackle these problems
otherwise we’ll get ourselves into
lots of trouble! But how? Part of the
way we can do this is to understand
how these changes will affect
animals and plants. To do that we
need to understand evolution! We
can use our modern knowledge to
help us conserve species, and cope
with invasive species and climate
change.
So, Darwin and evolution are
proving very useful right now!
How have some species changed over time?
The ancestral kiwi
Tokoeka (Apteryx australis) are thought to be
similar to the ancestor of our brown-coloured
kiwi. They had short beaks and bigger wings.
Modern day kiwi
• Modern day kiwi have long, slender beaks and
tiny wings unsuitable for flying.
Ancestral Whales
• The early whales had long slender legs and a long
tail. They lived near the waters edge.
Modern Whales
Now whales have lost the ability to walk and
they have only tiny back leg bones. Their front
legs are used for swimming
Ancestral Horses
The early horses were about the size of a dog.
Ancestral horse
• The early ancestors of the modern horse
walked on several spread-out toes, because
they walked on the soft, moist grounds of
primeval forests. They changed from eating
leaves to eating grasses so their teeth got
larger and stronger. They needed to run faster
so their legs go longer and they lifted their
toes off the ground. This meant that their
weight was carried on their 3rd toe which was
the longest.
Large Southern Land Mass
Kiwi are part of a bird family called 'ratites' and are
related to African ostriches, the South American rhea
and Australian emus. All the ratites probably
originated from Gondwanaland, the super-continent
that 80 million years ago began splitting into pieces
that include Australia and New Zealand.
Ostrich, rhea, cassowary and kiwi
The ostrich, rhea, cassowary and kiwi are all related birds that had a common ancestor
in Gondwana. (the large southern supercontinent we were once part of)
They are now distributed across New Zealand, South America, South Africa and Australia.
(Top left to right clockwise: Ostrich, rhea, kiwi and cassowary.)
New Zealand’s Unique Ecology
New Zealand has a rich and unique range of plants,
animals and fungi. The level of distinctive
biodiversity is as high as such world-renowned
ecosystems as the Galapagos Islands. So how have
our unique ecosystems developed? Visit the Science
Learning Hub to find out
http://www.sciencelearn.org.nz/Contexts/HiddenTaonga/Looking-Closer/New-Zealand-s-uniqueecology
Our very own!
• Approximately 65 million years
ago when the last land bridge to
Gondwana was lost, the flora,
fauna and fungi of New Zealand
began to evolve in isolation. As a
consequence, many of our native
species – like the kauri, kahikatea,
tōtara, rimu, tuatara, kiwi, kauri
snail and wētā – have become
uniquely adapted to life on our
islands and now only exist in this
country.
Travelled over the sea to get here
Some species were able to reach New Zealand
after the separation from Gondwana by floating
on currents or being blown by the wind, a
process that continues today. Plants such as
mānuka, rātā, flax and pōhutukawa,
and
Birds such as the saddleback, kōkako and huia (now
extinct), and our native bats all originated in other
lands and travelled across the sea. Once here, these
species have evolved separately from their relatives in
Australia or South America and, over time, have
developed as specialised inhabitants of the New
Zealand islands.
Then something happened..
• Around the time that New Zealand was losing the
last of its land connections to other land masses,
a dramatic event occurred that resulted in one of
the most devastating loss of species that has ever
been recorded. There are different explanations
for this loss – some scientists think a meteor hit
the earth, others suggest a series of volcanic
eruptions blanketed the atmosphere with smoke.
Whatever the cause, the result was the mass
extinction of the dinosaurs and other species.
• Before the mass extinction of the dinosaurs,
the reptiles had dominated, but within a very
short period of time, close to 85% of all
species were wiped out, and the mammals
began to occupy the vacant ecological niches –
everywhere, that is, except New Zealand.
But few mammals
• For reasons that are not
apparent, New Zealand was not
inhabited by many mammals.
Instead, our fauna became
dominated by birds and insects.
Birds became the predators, the
scavengers, the herbivores and
the insectivores. They lived
everywhere from the highest
mountains to the sea. With few
predators, many lost the ability to
fly and became ground dwellers.
Insects evolved to extremes of
big and small and occupied a
range of habitats.
We are unique..
• This process has made New Zealand unique –
nowhere else on the planet has such a range
of bird life and insect life, with only two
species of bat representing the mammals.