Natural Selection

• On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life

• This is quite a title!

• But it does suggest that Natural Selection must play an important role in the creation of new species

The Origin of Species

• Natural Selection is the way in which nature favours the reproductive success of some individuals within a population over others

• In other words, some individuals are more likely to pass their genes along than others

But what is natural selection?

How Natural Selection Works

• Success can take many forms1. Better suited to

gathering resources in a population

2. Better able to avoid predators

3. Ability to adapt to a unique environment

• There is no single recipe for success

1. Gathering Resources• Cheetahs• A faster cheetah is more

likely to catch its prey than a slower cheetah

• Faster cheetahs are more likely to eat regularly and stay alive

• So on average, faster cheetahs are more likely to reproduce and will have more offspring than slower cheetahs

• Darwin’s Finches• Variation in the size and

shape of beaks• Each species has evolved

to feed on unique things• Differences in diet mean

that they do not compete with each other for resources

1. Gathering Resources

• Anteaters• Ant colonies can be large tunnel complexes• Ancestors of anteaters with longer noses and tongues found it

easier to eat ants directly out of the colony• They were more likely to pass their genes and anteaters now

have very long noses and tongues

1. Gathering Resources

• Camouflage• The ability to blend in with

surroundings provides an advantage in evading predators

• An insect that looks more like a leaf, for example, than another is more likely to be mistaken for a leaf and more likely to be ignored by a predator

• This camouflage is more likely to be passed along to future generations

2. Avoiding Predators

Example of Camouflage

• Common Potoo

• Cactus• Found mostly in dry, arid places• Waxy coating helps keep water

from evaporating• Animals living in the desert eat

plants for moisture• Cacti have developed spikes to

deter predators• Since cacti with spikes are less

likely to be eaten, they are also more likely to breed and pass on their genes

2. Avoiding Predators

3. Adaptations to a Unique Environment

• A characteristic or feature of a species that makes it well suited for survival or reproductive success in its environment

3. Adaptations to a Unique Environment

3. Adaptations to a Unique Environment

• Fennec Fox• Fennec foxes live in the

desert• Have large ears to

dissipate heat• Fennec foxes with large

ears are less likely to over heat in the desert and are more likely to breed

• Remember the cactus, with its waxy coating?

• This coating prevents water evaporation in a hot, arid environment

3. Adaptation to a Unique Environment

• The polar bear• Among the largest bears• Has both a heavy double layer of fur and a layer of fat 4-5

inches thick, to survive extreme cold• They are very strong swimmers

– Why might this be important?

3. Adaptation to a Unique Environment

• They are very strong swimmers– Why might this be

important?– They live in oceanic

areas and often live on areas of the sea frozen only during the winter months

• They blend well into their surroundings, making it harder for prey to spot them

3. Adaptation to a Unique Environment

• The Theory of Natural Selection allowed Darwin to make predictions he could not prove at the time (theory!)

• He predicted that, based on the location of great apes today, we would find fossil evidence of human ancestry in Africa (biogeography!)

Predictions

• Darwin’s orchid: flower with a very long spur– He predicted an insect must exist with a very long

proboscis, in order to pollinate it– Madagascan Hawk Moth discovered in 1903

Predictions

• Over the next several slides, you’ll see some species that in some way demonstrate natural selection

• Your job is to decide how that species has been affected by natural selection, or to decide which animal is most likely to pass it genes along

The Natural Selection Game

Giraffe

Roses

Walking Stick

The Cobra

Blue Shark

Venus Fly Trap

Octopus

Pangolin

Buckeye Butterfly

Angler Fish

Bee Orchid

• A characteristic or feature of a species that makes it well suited for survival or reproductive success in its environment

Adaptation

• Explains why the cactus can be successful in the desert

Adaptation

• This phrase has been used to describe Darwin’s theory

• Is this misleading?

Survival of the Fittest

• Directional Selection

• Stabilizing Selection

• Disruptive Selection

Types of Selection

• Selection that favours an increase or decrease in the value of a trait from the current population average

Directional Selection

Directional Selection

Antibiotic Resistance in Bacteria

• Selection against individuals exhibiting traits that deviate from the current population average

Stabilizing Selecton

Stabilizing Selection

Birth weight in human babies

• Favours two or more variations of a trait that differ from the current population average

Disruptive Selection

Disruptive Selection

Rock Pocket Mouse

• Some populations have adapted to living at extreme heights

• Able to survive despite low oxygen levels

A Human Example

"The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!”

Darwin

Homework Questions

• PG. 335 #2, 6, 11• PG. 372 #17, 32