Artificial Selection

Breeding for a purpose

All our modern breeds of dog are descended

from the wolf.

So how come they all look and act so differently?

Loyal and intelligent

Small and friendly

Large and strong

Hard-working with a thick coat

Courageous, with a very strong jaw

Very fast and agile

Gamekeepers in the 1800s had a problem. Poachers were entering their land and stealing their game-birds before the shooting season. Their dogs (mastiffs) were big, strong dogs and great companions but they were not aggressive or fast enough to chase after the poachers.

Mastiff Bulldog

Another breed known to them was the bulldog. This was quick and aggressive but not strong enough to pull the poachers down and hold them until a gamekeeper arrived.

What could they do?

Humans have changed the way dogs look and act by choosing which dogs to breed together.

Mastiff – large and strong but slow and not aggressive.

Bulldog – Aggressive and quick but small.

Bullmastiff – Large, quick, strong and aggressive

This is called

Selective Breeding

Perfect!

+

This dog is a more modern example of selective breeding.

It is a relatively new breed called a labradoodle.

What two dogs do you think were bred to make it?

Where did your breed come from?

Dogs bred as sighthounds - clockwise from top left: Whippet, Borzoi, and Saluki

Can you see the similarities in their anatomy?

What physical characteristics do you think were selected?

14th century print of a hunt.

Can you spot the sight-hounds?

How did you decide?

Dogs bred as herding dogs – clockwise from top left – Border collie, Lancashire heeler, Rottweiler, Old English Sheepdog

Do you think the characteristics that are bred for are physical or behavioural?

Why?

Dogs – bred for a purpose

• Dogs have been selectively bred for a purpose for more than 3000 years.

• Starting with some wolves, dogs were initially bred to help with:– hunting; producing hounds, terriers, and

retrievers– farming; producing herding dogs and guard

dogs

• Modern breeding has given us companion dogs and toy dogs – whose purpose is to keep us company… funnily enough

Meat

Dairy

Draft

The Auroch – where all domesticated cattle were bred from

Artificial selection in plants

Wheat

• Tall wheat plants have a high yield, but are easily damaged in wind and rain

• Dwarf wheat plants have a low yield, but are robust against nasty weather

• Q: What do you think happened when the two types were cross-bred?

• A: A dwarf wheat with high yield that was robust!

• Other types were produced, but they were discarded

• Discuss how you would breed for:

– Better quality of milk from cows

– - Increased number of offspring in sheep

How would you…?

In summary…

• Selective breeding = Artificial selection

• Has been used for animals and plants

• The method:– The desired characteristics are identified– They are bred together– Only the offspring exhibiting the desired

characteristics are bred– This is repeated over several generations until

the desired trait is fully developed

In summary…

• Problems:• Traits are chosen to benefit humans, not

the animal– Physical problems often occur in domestic

animals eg. Inflammation of the udder (mastisis) in cows due to increased milk production

• Usually involves inbreeding, which can lead to reduced genetic diversity

Would it be right to selectively breed humans??

• Adolf Hitler believed in a master race (the Aryans) and implemented a plan to create this race.

• This involved eugenics – the selective breeding of humans.

Nazi eugenics

• Those considered “not worthy of life”, - let alone allowed to have children - included (but was not limited to) the criminal, degenerate, dissident, feeble-minded, homosexual, idle, insane, and the weak

• 400,000 people were sterilised against their will and 70,000 were killed

What do YOU think?