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.

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.

NATURAL SELECTION – VISTA!

• Natural selection causes populations of

living things to change over time.

• In fact, it can be broken down into five

basic steps, abbreviated here as V.I.S.T.A.

• V - Variation

• I - Inheritance

• S - Selection

• T - Time

• A - Adaptation

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

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

VARIANCE OR VARIATION:

• Members of any given species are seldom

exactly the same, either inside or outside.

• Organisms can vary in size, coloration, ability

to fight off diseases, and countless other

traits.

• Such variation is often the result of random

mutations, or "copying errors," that arise

when cells divide as new organisms

develop.

VARIANCE OR VARIATION:

• If the organism survives and reproduces, their

genes get passed on

• If the gene is either neutral or positive, it is more

likely that the mutation will be passed on to the

next generation

• Differences in color, for instance, aid some

individuals in camouflaging themselves from

predators. Sharper eyes and claws help an eagle

catch its dinner. And brighter coloration improves

a male peacock's chances of attracting a mate.

• Next, let’s look at a few examples of variations

EXAMPLE 1 OF VARIETY OF TRAITS: FUR COLOR OF ORGANISMS

EXAMPLE 2 OF VARIETY OF TRAITS: COUNTER-SHADING IN MARINE LIFE

• 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 for each of

these species?

EXAMPLE 3 OF VARIETY OF TRAITS: BEAKS IN BIRDS

EXAMPLE 4 OF VARIETY OF TRAITS:CLAWS IN BIRDS

Variation in talon size and shape due to hunting technique.

INHERITANCE:

• When organisms reproduce, they pass on their

DNA--the set of instructions encoded in living

cells for building bodies--to their offspring.

• And since many traits are encoded in DNA,

offspring often inherit the variations of their

parents.

• Tall people, for example, tend to have tall

children.

SELECTION: SURVIVAL AND REPRODUCTION

• Environments cannot support unlimited

populations.

• Resources are limited, more organisms are born

than can survive: some individuals will be more

successful at finding food, mating or avoiding

predators and will have a better chance to

thrive, reproduce, and pass on, their DNA.

• Small variations can influence whether or not

an individual lives and reproduces.

TIME:

• In generation after generation, advantageous

traits help some individuals survive and

reproduce.

• And these traits are passed on to greater and

greater numbers of offspring.

• After just a few generations or after thousands,

depending on the circumstances, such traits

become common in the population.

ADAPTATION:

• The result is a population that is better suited--better

adapted--to some aspect of the environment than

it was before. Legs once used for walking are

modified for use as wings or flippers. Scales used for

protection change colors to serve as camouflage.

THE MAN BEHIND IT ALL:

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.

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.

This isolation of the islands

allowed geographical

isolation to take place

GEOGRAPHIC ISOLATION

• Species evolved differently 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.

Darwin’s Conclusions – based on his research:

• 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.

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?

TO SUM IT UP…

• Watch this: Natural Selection

video

HW – NATURAL SELECTION WKSHT