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

premolars/molars

2,3,4

coat length short, medium, long

tail length short, medium, long

number of claws on hind

feet

4, 5

size small, medium, large

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. Micesuffering from these mites itch and scratch themselves untilthey develop open wounds which become badly contaminatedwith bacteria. The mice lose weight and eventually die due toserious bacterial infection. The mice which are much moreprone to picking up and harbouring the mites are those withcurly 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.....