7 . 1 1 C I D E N T I F Y S O M E C H A N G E S I N T R A I T S T H A T H A V E

O C C U R R E D O V E R S E V E R A L G E N E R A T I O N S T H R O U G H

N A T U R A L S E L E C T I O N A N D S E L E C T I V E B R E E D I N G

NATURAL SELECTION

COULD YOU HAVE RIDDEN A HORSE MILLIONS OF YEARS AGO?

• Horse evolution goes back more than

55 million years

EVOLUTION OF THE HORSE THE ECOLOGICAL PRESSURES FACING THE SPECIES DETERMINED THE TYPE OF DIFFERENCES, OR VARIATION

The development of larger limbs

and hooves allowed horses to

spread out and become more

successful in grassland habitats

as they developed.

HOW DO GENETICS CHANGE OVER SEVERAL GENERATIONS?

• Changes occur over time from either natural

selection or selective breeding

• You now know that when DNA is copied,

mutations (mistakes) can occur

• Sometimes those mistakes are fatal, some

times they make no difference in survival,

and sometimes, every once in a great while,

that mutation becomes critical to survival

WHY CAN YOU RIDE ONE NOW?

• Natural selection caused some changes in

horses, and humans participated in selective

breeding which both domesticated the horse

and made specialized organisms.

WHAT EXACTLY IS NATURAL SELECTION?

• The process by which individuals that are

better adapted to the environment survive

and reproduce more successfully than other

members of their species

• These are changes in genetics traits over

many generations

WHO FIGURED THIS OUT?

• CHARLES DARWIN – 1809-1882

• Most people in the world did not

become aware of the theory of

evolution until 1859, when Charles

Darwin published his book On the

Origin of Species by Means of

Natural Selection.

DARWIN’S OBSERVATIONS

• This book described the observations and evidence

that he collected over 20 years of intensive

research, beginning with a five-year voyage around

the world on a British research ship, the HMS Beagle.

• During this five-year voyage, Darwin was able to

make observations about plants and animals

spread around the world, and to collect specimens

to study when he returned to England.

DARWIN’S JOURNEY

• Each time the Beagle stopped at a port to do some

trading, Darwin went on land to explore and look

for the local plants, animals, and fossils. One of the

most important things Darwin did was to keep a

diary. He took extremely detailed notes and

drawings about everything he saw as well as his

thoughts.

• http://www.nhm.ac.uk/nature-online/science-of-

natural-history/expeditions-collecting/beagle-

voyage/

THE GALAPAGOS ISLANDSDarwin’s best known

discoveries were made on

the Galápagos Islands, a

group of 16 volcanic

islands near the equator

about 600 miles from the

west coast of South

America.

Allowed geographical

isolation to take place

GEOGRAPHIC ISOLATION

• Species evolved differently in on the islands than on

the “mainland”

• Darwin was amazed by the array of life he saw on

the Galápagos Islands. He saw animals unlike

anything he had ever seen before.

• For example, the iguanas (large lizards) differed

between islands. The members of one iguana

species spent much of their time swimming and

diving underwater for seaweed, while those of

another iguana species lived on land and ate

plants.

SIMILARITIES AND DIFFERENCES

Marine Iguanas of the Galapagos

Large claws for gripping slippery rocks, eat seaweeds

Green iguanas in South America

Smaller claws for climbing trees, eat leaves

Marine Iguanas

WHAT DOES THIS MEAN?

Key understanding: mainland species were still related to the island species -

Curiously, they looked different, ate different foods, and behaved differently, but still had some similarities

So how did this happen?

Answer: gradual changes over many generations

Darwin’s observations

• Of particular interest were the finches on these islands

• They had varied sizes and shapes of the beaks. This observation made him wonder….

WHY?

FROM ONE FINCH…

• There are now at least 13 species of finches on the

Galapagos Islands, each filling a different niche on

different islands. All of them evolved from one

ancestral species, which colonized the islands only

a few million years ago.

WHAT DARWIN LEARNED FROM THESE FINCHES

• The one species of finch gradually evolved into separate species because of food sources and other environmental factors such as amount of water available

For example:• Beaks highly adapted to food source

• Large beaks - meant there was little rainfall because the seeds were large & tough

• Small beaks - Heavy rainfall – seeds – small & soft

• Other adaptations were sharp beaks for finding and eating insects, wide beaks for cracking seeds

THE FINCHES ALSO EVOLVED TO EAT A VARIETY OF FOODS -

MORE ADAPTATIONS

• Darwin studied hundreds more animal

and plant species. After nearly 20

years of research, he proposed

his theory of evolution by natural

selection.

• Another example of what he studied:

THE GALAPAGOS TORTOISE

The giant tortoises (Geochleonenigra) in the Galapagos 2 m long

Saddle-shaped shell, long necksmore prone to standing upright to

forage on cactus

Nearest relative- Chacos Tortoise

(Geochelone chilensis) in Argentina just 20cm long

Dome-shaped shell, short necks

graze on ground level vegetation

Theory of Natural Selection(Darwin’s Conclusions)

• Species have changed over generations through adaptations• The changes allow them to survive and reproduce in a new environment. • Darwin proposed that evolution occurs by means of natural selection• New species may form when a group of individuals is isolated from the rest of the population

Darwin’s 5 key points in theTheory of Natural Selection:

1. Populations have (genetic) variations.

2. Some variations are favorable.

3. More offspring are produced than

survive

4. Those offspring that survive have

favorable traits. 5. A population will change over time.

NATURAL SELECTION - QUICK EXPLANATION

How is this an example of natural selection?

Green bugs are more visible to its predator

Green bugs get eaten more easily

Brown bugs not as visible, they survive

Brown bugs reproduce, the helpful alleles for the brown color are passed on to the next generation

After many generations, more members will be brown

The environment has “selected” organisms with the helpful traits, hence the term “natural selection”

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://evolution.berkeley.edu/evolibrary/home.php

MYTHBUSTING!

• Survival of the “fittest” – what does that mean?

Fitness is the key to natural selection. We're not talking

about how many reps you can burn through at the gym --

biological fitness is an organism's ability to successfully

survive long enough to reproduce.

Beyond that, it also reflects an organism's ability to

reproduce well. It isn't enough for a tree to create a bunch of

seeds. Those seeds need the ability to end up in fertile soil

with enough resources to sprout and grow.

DARWIN’S CONTEMPORARIES

• Lamarck and Wallace had similar findings as Darwin• Wallace called the changes in species over time “evolution”.

Jean-Baptiste Lamarck, 1744-1829

Alfred Russell Wallace, 1823-1913 (with Darwin)

YOU MAY HAVE HEARD OF…

• Lamarckism (or Lamarckian inheritance) is

the idea that an organism can pass on

characteristics that it acquired during its

lifetime to its offspring.

FACTORS AFFECTING NATURAL SELECTION

1. Overproduction

2. Competition

3. Variations

OVERPRODUCTION

• What’s the point of so many offspring?

• Only the “fittest” survive, not all of your

offspring will survive long enough to

reproduce and pass on genetic heredity–

but some will!

COMPETITION

• Resources are limited! There is only so much

food, space, water and shelter

Members of the same species must compete

with each other, only the fittest survive

AND VARIATION ….

Any genetic difference between individuals of the same species

• very important in natural selection

• the stronger individuals survive and reproduce

• offspring with helpful traits will survive and then pass along those traits to their offspring

What might those

traits be?

EXAMPLE 1 OF VARIETY OF TRAITS: COUNTER-SHADING IN FISH

• Upper side of the animal is darker than the lower

side, blends in with sea floor

• Lower side of organism is lighter, organism blends in

with its surroundings – in this case the sky

Which do you think is better for the survival of these

species?

EXAMPLE 2 OF VARIETY OF TRAITS: BEAKS IN BIRDS

EXAMPLE 3 OF VARIETY OF TRAITS:CLAWS IN BIRDS

Variation in talon size and shape due to hunting technique.

TO SUM IT UP…

• Watch this: Natural Selection

video

HW – NATURAL SELECTION WKSHT