Transcript Natural Selection - Education Scotland

Natural selection
WALT
• Understand the principle of natural
selection
• Describe features which may be beneficial
to an organism’s survival and explain why
they may be of advantage
Charles Darwin
'survival of the fittest'
is not of those organisms that were most
fit, but of those most well adapted to
surviving in their surroundings.
'natural selection'
is a process in which individuals which
are better adapted to their environment
survive and breed, whilst those less well
adapted fail to do so.
'evolution'
is the change over time due to the
presence of variation within species
Start by drawing the outline of your
mouse
Now choose one possibility from each feature
FEATURE
POSSIBILITIES
coat colour
black, brown, grey, albino
coat depth
fine, medium, thick
coat shape
curly, wavy, straight
eye location
more central in skull, lateral, more lateral
whisker length
short, medium, long
claw length
short, medium, long
whiskers
10, 15, 20 each side of face
number of pairs of
2,3,4
premolars/molars
coat length
short, medium, long
tail length
short, medium, long
number of claws on hind
4, 5
feet
And so the story begins.....
On a dark night.....
Hungry owls come out hunting at night. All the
white mice were much more easily spotted,
so the owls ate all the white mice.....
As the winter gets much colder, some mice face
difficulties keeping warm despite the freezing
temperatures and die due to hypothermia. Only the
mice with medium or thick coats survive...................
Over the summer, a serious outbreak of mites occurs. Mice
suffering from these mites itch and scratch themselves until
they develop open wounds which become badly contaminated
with bacteria. The mice lose weight and eventually die due to
serious bacterial infection. The mice which are much more
prone to picking up and harbouring the mites are those with
curly coats which eventually die off..............
• As the winter kicks in, predators are on the hunt again for scarce food
sources. Those mice with eyes located laterally are able to spot and hide
from predators such as owls on the hunt. Those with eyes located more
centrally in the skull are unable to do so, therefore they quickly die of due to
high levels of predation.
• In the warm summer,
mice reproduce and
very quickly become a
pest to humans in the
area. The council lays
hundreds of traps
throughout the entire
summer period.
• Only those with medium
and long whiskers of at
least 15 in number on
each side are able to
detect the mouse traps
and avoid the trap.
Those with short, few
whiskers die off...........
• The damp, fairly warm Autumn
season provides ideal
conditions for growth of a
fungus Trichophyton
mentagrophytes. Untreated, this
develops into a painful fungal
infection in the feet of the mice,
leaving them unable to retreat
from predators as quickly as
previously. Those with long
claws harbour this fungus much
more seriously and therefore
die off due to increased
predation.
• A long, cold winter
sees the main food
source for the mice
– seeds – freeze for
long periods of time.
• Only the mice with
sufficient molars are
able to mechanically
break down the
seeds enough to
release the nutrients
inside throughout
digestion. All those
mice with only 2
pairs of molars
suffer death due to
starvation.
And so now we see,
through years of natural selection,
surviving the odds of nature,
and all the battle in between,
we have developed the ultimate,
strongest, fittest,
most cunning mouse of all time.....