Transcript Variation and Evolution - Christchurch Girls' High School

Variation and Evolution
Charles Darwin
• Charles Darwin was a brilliant naturalist who
changed the way people think about life on
earth. One reason why he was able to do this was because he
was always passionate about science and nature!
• From a young age Darwin collected lots of different things
like stones and beetles and performed experiments with his
brother in the garden shed. It was this early interest that
helped him become a great man!
• Read more about Darwins Life:
http://www.christs.cam.ac.uk/darwin200/pages/index.php?p
age_id=j1
What is
Evolution?
• Evolution is the slow process that changes
animals and plants and it’s a great piece of
science! It describes loads of things in nature
like fossils, peacocks' tails, lions’ teeth, birds’
wings and human brains, just to name a few.
It is also supported by lots and lots of
evidence that has been collected by scientists
for more than 150 years!
How do species evolve (change over
time)
This links clearly explains how species evolve.
Scroll down to the question ‘How do species
evolve’
http://www.christs.cam.ac.uk/darwin200/pages
/index.php?page_id=j2
So this is Natural Selection!
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!
Why is knowing about Evolution
important?
Take a look at this:
http://www.christs.cam.ac.uk/darwin200/docs/
content/why_evolution.pdf
Variation
• For evolution by natural selection to occur
there must be slight differences between
members of a population. For example
differences in size, colour, behaviour etc .
What do these differences mean?
Some individuals will be better suited to the
environment than others. This may mean that
some individuals are better camouflaged and
therefore not 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 genes 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.
Natural selection
Variation
Individuals show variation:
some variations are more
favorable than others
Lots of babies
Population produces too
many offspring, many will
die
Natural Selection
Natural selection favors the
best suited at the time
Inheritance
Variations are inherited. The
best suited variants leave
more offspring.
Modelling Natural Selection
• Scattered around the room are different coloured
butterflies. You are an insectivorous bird and you have 20
seconds to catch as many butterflies as you can with your
‘beak’ (between thumb and forefinger).
•
•
•
•
How many different phenotypes did you find?
How many butterflies of each phenotype did you catch?
How many of each phenotype did the whole class catch?
The population contained 80 red, 80 black and 80 clear
butterflies. Which ones were the best at avoiding
predation? Why were they more successful?
• What is likely to happen to the proportions of each
phenotype in the next generation? Why will this happen?
• What was the ‘selection pressure’ operating in this model?
Darwin’s Theory of
Evolution by
Natural Selection.
Darwin’s 5 points
1.
2.
3.
4.
5.
Population has variations.
Some variations are favorable.
More offspring are produced than survive
Those that have favourable traits survive.
A population will change over time as the
individuals with the more favourable
characteristics survive and pass their
genes on to the future generation.
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.
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 this, 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.