Download 2 How Do Population Changes Happen?

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4ENNESSEE 3CIENCE
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!FTER YOU READ THIS SECTION YOU SHOULD BE ABLE TO ANSWER
THESE QUESTIONS
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',% ',% s 7HO WAS #HARLES $ARWIN
s 7HAT IDEAS AFFECTED $ARWINS THINKING
s 7HAT IS NATURAL SELECTION
7HO 7AS #HARLES $ARWIN
)N #HARLES $ARWIN GRADUATED FROM COLLEGE
!LTHOUGH HE EVENTUALLY EARNED A DEGREE IN RELIGION $ARWIN
WAS MOST INTERESTED IN THE STUDY OF PLANTS AND ANIMALS
$ARWINS INTEREST IN NATURE LED HIM TO SIGN ON FOR A
FIVEYEAR VOYAGE AROUND THE WORLD (E WAS A NATURALIST
ON THE (-3 "EAGLE A "RITISH SHIP ! NATURALIST IS SOME
ONE WHO STUDIES NATURE $URING THE TRIP $ARWIN MADE
OBSERVATIONS THAT HELPED HIM FORM A THEORY ABOUT HOW
CHANGES IN THE TRAITS OF POPULATIONS HAPPEN 4HESE IDEAS
CAUSED SCIENTISTS TO CHANGE THE WAY THEY THOUGHT ABOUT
THE LIVING WORLD
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3UMMARIZE !FTER YOU READ
THIS SECTION MAKE A CHART
SHOWING THE FOUR STEPS OF
NATURAL SELECTION )N THE CHART
EXPLAIN WHAT HAPPENS AT
EACH STEP
$!27).3 */52.%9
/N THE TRIP $ARWIN OBSERVED PLANTS AND ANIMALS FROM
MANY PARTS OF THE WORLD /NE PLACE $ARWIN FOUND INTERESTING
WAS THE 'ALÈPAGOS )SLANDS 4HESE ISLANDS ARE LOCATED ABOUT
KM WEST OF %CUADOR A COUNTRY IN 3OUTH !MERICA -ANY
UNUSUAL ORGANISMS LIVE ON THE 'ALÈPAGOS )SLANDS
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#ONVERT !BOUT HOW FAR
ARE THE 'ALÉPAGOS )SLANDS
FROM %CUADOR IN MILES
KM MI
4HIS LINE SHOWS THE COURSE OF THE (-3 "EAGLE
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$ESCRIBE 7HICH CONTINENT
ARE THE 'ALÉPAGOS )SLANDS
CLOSEST TO
$ARWIN STUDIED PLANTS AND ANIMALS ON THE 'ALÉPAGOS )SLANDS
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)NTERACTIVE 2EADER AND 3TUDY 'UIDE
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0OPULATION #HANGES
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$ESCRIBE 7HAT DID
$ARWIN OBSERVE ABOUT THE
lNCHES ON THE 'ALÉPAGOS
)SLANDS
$ARWIN OBSERVED THAT THE ANIMALS AND PLANTS ON THE
'ALÈPAGOS )SLANDS WERE SIMILAR TO THOSE IN %CUADOR
(OWEVER THEY WERE NOT IDENTICAL &OR EXAMPLE $ARWIN
CLOSELY OBSERVED BIRDS CALLED FINCHES 4HE FINCHES ON THE
'ALÈPAGOS )SLANDS WERE SLIGHTLY DIFFERENT FROM THE FINCHES
IN %CUADOR )N ADDITION THE FINCHES ON EACH ISLAND IN THE
'ALÈPAGOS DIFFERED FROM THE FINCHES ON THE OTHER ISLANDS
$ARWIN HYPOTHESIZED THAT THE ISLAND FINCHES WERE
DESCENDENTS OF 3OUTH !MERICAN FINCHES (E THOUGHT THE
FIRST FINCHES ON THE ISLANDS WERE BLOWN THERE FROM 3OUTH
!MERICA BY A STORM (E SUGGESTED THAT OVER MANY GEN
ERATIONS ADAPTATIONS AROSE IN THE FINCH POPULATION THAT
HELPED THEM SURVIVE IN THE DIFFERENT ISLAND ENVIRONMENTS
&OR EXAMPLE THE BEAKS OF DIFFERENT FINCH SPECIES ARE
ADAPTED TO THE KIND OF FOOD THE SPECIES EAT
4HE LARGE GROUND lNCH HAS A WIDE
STRONG BEAK )T CAN EASILY CRACK OPEN
LARGE HARD SEEDS )TS BEAK WORKS
LIKE A NUTCRACKER
4HE CACTUS lNCH HAS A TOUGH BEAK )T
USES ITS BEAK TO EAT CACTUS PARTS AND
INSECTS )TS BEAK WORKS LIKE A PAIR OF
NEEDLENOSE PLIERS
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)NFER 7HAT CAN YOU GUESS
ABOUT THE ENVIRONMENT IN
WHICH THE CACTUS lNCH LIVES
BASED ON THE INFORMATION
IN THE lGURE %XPLAIN YOUR
ANSWER
4HE WARBLER lNCH HAS A SMALL
NARROW BEAK )T CAN CATCH SMALL
INSECTS WITH ITS BEAK )TS BEAK
WORKS LIKE A PAIR OF TWEEZERS
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)NTERACTIVE 2EADER AND 3TUDY 'UIDE
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0OPULATION #HANGES
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(OW $ID $ARWIN $EVELOP (IS 4HEORY !BOUT
#HANGE /VER 4IME
!FTER $ARWIN RETURNED TO %NGLAND HE SPENT MANY YEARS
THINKING ABOUT HIS EXPERIENCES ON THE TRIP )N $ARWIN
PUBLISHED A FAMOUS BOOK CALLED /N THE /RIGIN OF 3PECIES BY
-EANS OF .ATURAL 3ELECTION )N HIS BOOK $ARWIN PROPOSED
THE THEORY THAT CHANGES IN THE TRAITS OF POPULATIONS OVER TIME
HAPPEN BY NATURAL SELECTION
.ATURAL SELECTION HAPPENS WHEN ORGANISMS THAT
ARE WELL ADAPTED TO THEIR ENVIRONMENT SURVIVE BUT LESS
WELLADAPTED ORGANISMS DO NOT 7HEN THE BETTERADAPTED
ORGANISMS REPRODUCE THEY PASS THEIR USEFUL TRAITS ON TO
THEIR OFFSPRING /VER TIME MORE MEMBERS OF THE POPU
LATION HAVE THESE TRAITS $ARWIN COMBINED IDEAS ABOUT
BREEDING POPULATION AND %ARTHS HISTORY TO COME UP WITH
A THEORY TO EXPLAIN HIS OBSERVATIONS
2%!$).' #(%#+
$ElNE 7HAT IS NATURAL
SELECTION
)$%!3 !"/54 "2%%$).'
)N $ARWINS TIME FARMERS AND BREEDERS HAD PRODUCED
MANY KINDS OF FARM ANIMALS AND PLANTS 4HEY LEARNED
THAT IF THEY BRED PLANTS OR ANIMALS THAT HAD A DESIRABLE
TRAIT SOME OF THE OFFSPRING MAY HAVE THE TRAIT ! TRAIT IS A
FORM OF AN INHERITED CHARACTERISTIC 4HE PRACTICE IN WHICH
HUMANS SELECT PLANTS OR ANIMALS FOR BREEDING BASED ON
DESIRED TRAITS IS CALLED SELECTIVE BREEDING
3ELECTIVE BREEDING SHOWED $ARWIN THAT THE TRAITS OF
ORGANISMS CAN CHANGE AND THAT CERTAIN TRAITS CAN SPREAD
THROUGH POPULATIONS &OR EXAMPLE MOST PETS SUCH AS THE
DOGS BELOW HAVE BEEN BRED FOR A VARIETY OF DESIRED TRAITS
/VER THE PAST YEARS PEOPLE HAVE SELECTIVELY BRED
DOGS TO PRODUCE MORE THAN BREEDS
2%!$).' #(%#+
%XPLAIN (OW DID IDEAS
ABOUT SELECTIVE BREEDING
CHANGE $ARWINS THINKING
ABOUT CHANGES IN THE TRAITS OF
POPULATIONS OVER TIME
0EOPLE HAVE SELECTIVELY BRED DOGS FOR DIFFERENT TRAITS 4ODAY THERE ARE
OVER DOG BREEDS
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)NTERACTIVE 2EADER AND 3TUDY 'UIDE
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0OPULATION #HANGES
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)DENTIFY !CCORDING TO
4HOMAS -ALTHUS WHAT ARE
TWO THINGS THAT CAN LIMIT THE
SIZE OF HUMAN POPULATIONS
$URING $ARWINS TIME A SCIENTIST NAMED 4HOMAS
-ALTHUS WAS STUDYING HUMAN POPULATIONS (E OBSERVED
THAT THERE WERE MORE BABIES BEING BORN THAN THERE WERE
PEOPLE DYING (E THOUGHT THAT THE HUMAN POPULATION
COULD GROW MORE RAPIDLY THAN FOOD SUPPLIES COULD GROW
4HIS WOULD RESULT IN A WORLDWIDE FOOD SHORTAGE -ALTHUS
ALSO POINTED OUT THAT THE SIZE OF HUMAN POPULATIONS IS
LIMITED BY PROBLEMS SUCH AS STARVATION AND DISEASE
$ARWIN REALIZED THAT -ALTHUSS IDEAS CAN APPLY TO ALL
SPECIES NOT JUST HUMANS (E KNEW THAT ANY SPECIES CAN
PRODUCE MANY OFFSPRING (E ALSO KNEW STARVATION DIS
EASE COMPETITION AND PREDATION LIMITED THE POPULATIONS
OF ALL SPECIES /NLY A LIMITED NUMBER OF INDIVIDUALS LIVE
LONG ENOUGH TO REPRODUCE
$ARWIN REASONED THAT THE SURVIVORS HAD TRAITS THAT
HELPED THEM SURVIVE IN THEIR ENVIRONMENT (E ALSO
THOUGHT THAT THE SURVIVORS WOULD PASS ON SOME OF THEIR
TRAITS TO THEIR OFFSPRING
)$%!3 !"/54 %!24(3 ()34/29
2%!$).' #(%#+
%XPLAIN (OW DID #HARLES
,YELLS BOOK CHANGE HOW
SCIENTISTS THOUGHT ABOUT
%ARTHS HISTORY
.EW INFORMATION ABOUT %ARTHS HISTORY ALSO AFFECTED
$ARWINS IDEAS ABOUT CHANGES IN POPULATIONS $URING
$ARWINS TIME MOST GEOLOGISTS THOUGHT THAT %ARTH WAS
VERY YOUNG "UT IMPORTANT BOOKS SUCH AS 0RINCIPLES
OF 'EOLOGY BY #HARLES ,YELL WERE CHANGING IDEAS ABOUT
THE %ARTH ,YELLS BOOK GAVE EVIDENCE THAT %ARTH IS MUCH
OLDER THAN ANYONE ONCE THOUGHT
$ARWIN BELIEVED THAT POPULATIONS CHANGE SLOWLY
$ARWIN REASONED THAT IF %ARTH WAS VERY OLD THERE WOULD
BE ENOUGH TIME FOR ORGANISMS TO CHANGE SLOWLY
M:D>:EHHD
$ESCRIBE &ILL IN THE BLANK
SPACES IN THE TABLE
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)NTERACTIVE 2EADER AND 3TUDY 'UIDE
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0OPULATION #HANGES
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.ATURAL SELECTION HAS FOUR STEPS OVERPRODUCTION
INHERITED VARIATION STRUGGLE TO SURVIVE AND SUCCESSFUL
REPRODUCTION
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/VERPRODUCTION ! TARANTULAS EGG SAC
CAN HOLD TO EGGS 3OME OF
THE EGGS WILL SURVIVE AND DEVELOP INTO
ADULT SPIDERS 3OME WILL NOT
JXp@k
'IVE %XAMPLES 4HE lGURE
SHOWS ONE EXAMPLE OF HOW
THE FOUR STEPS OF NATURAL
SELECTION CAN WORK )N A
GROUP TALK ABOUT THREE OR
MORE OTHER EXAMPLES OF HOW
NATURAL SELECTION CAN AFFECT
POPULATIONS
)NHERITED 6ARIATION %VERY
INDIVIDUAL HAS ITS OWN COMBINATION
OF TRAITS %ACH TARANTULA IS SIMILAR
BUT NOT IDENTICAL TO ITS PARENTS
M:D>:EHHD
3TRUGGLE TO 3URVIVE 3OME TARAN
TULAS MAY HAVE TRAITS THAT MAKE IT
MORE LIKELY THAT THEY WILL SURVIVE
&OR EXAMPLE A TARANTULA MAY BE
BETTER ABLE TO lGHT OFF PREDATORS
SUCH AS THIS WASP
3UCCESSFUL 2EPRODUCTION 4HE
TARANTULAS THAT ARE BEST ADAPTED
TO THEIR ENVIRONMENT ARE LIKELY
TO SURVIVE AND REPRODUCE 4HEIR
OFFSPRING MAY INHERIT THE TRAITS THAT
HELP THEM TO SURVIVE
)DENTIFY 7HY ARE SOME
TARANTULAS MORE LIKELY TO
SURVIVE THAN OTHERS
'%.%4)#3 !.$ #(!.'%
$ARWIN KNEW THAT ORGANISMS INHERIT TRAITS BUT NOT
HOW THEY INHERIT TRAITS (E ALSO KNEW THAT THERE IS GREAT
VARIATION AMONG ORGANISMS BUT NOT HOW THAT VARIATION
HAPPENS 4ODAY SCIENTISTS KNOW THAT GENES DETERMINE
THE TRAITS OF AN ORGANISM 4HESE GENES ARE EXCHANGED AND
PASSED ON FROM PARENT TO OFFSPRING
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)NTERACTIVE 2EADER AND 3TUDY 'UIDE
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0OPULATION #HANGES
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