中学生百科英语3

中学生百科英语3-Cause&Effect

BurkeandWills:AcrossAustralia

AlexandraDavid-Neel:AFrenchWomaninTibet

VitusBering:AcrossSiberiatoNorthAmerica

RobertScott:ARacetotheSouthPole

IntotheDeep:OceanExploration

WorldPopulationGrowth

ChangesintheFamily

WomenandChange

RainForest

TheGarbageProject

Roadrunners

AfraidtoFly

LanguagesandLanguageDiversity

Skyscrapers

Left-Handedness

BiospheresinSpace

Earthquakes

SnowandHail

PhotovoltaicCells:EnergySourceoftheFuture

BiologicalClocks

Headaches

SleepandDreams

HealthCareandEpidemics

Medicine:FromLeechestoLasers

CholesterolandHeartDisease

1BurkeandWills:AcrossAustralia

Australiaisahugecountry,andtheoutback(theAustralianwordfortheinteriorofthecountry)isdesert.Insomeyears,itrainsonlyeightcentimetersintheoutback,butinotheryears,rainstormsturnthedesertintosandyswamps.

Untiltheeighteenthcentury,onlyaborigineslivedinAustralia.ThesearethefirstpeoplewholivedinAustralia.WhenEuropeanswenttheretolive,theybuilttownsonthecoast.However,inthe1850s,peoplebeganthinkingmoreabouttheinterior.

In1860,RobertO'HaraBurke,apoliceofficerfromIreland,waschosentoleadanexpeditionacrossthecontinentfromsouthtonorth.HetookwithhimWilliamJohnWillsandelevenothermen,camels,horses,andenoughsuppliesforayearandahalf.TheyleftMelbournefortheGulfofCarpentariaonAugust20,winterinthesouthernhemisphere.

Theexpeditionhadproblemsfromthebeginning.Burkehadnoexperienceintheoutback.Themenfoughtandwouldnotfolloworders.Twicetheyleftsomeoftheirsuppliessothattheycouldmovefasterandlatersentoneofthemen,WilliamWright,backforthem.

Finally,asmallgroupledbyBurkemovedonaheadoftheotherstoarivernamedCooper'sCreekandsetuptheirbasecamp.Theywerehalfwayacrossthecontinent,butitwassummernow,withveryhotweatherandsandstorms.

TheywaitedamonthforWright,andthenBurkedecidedthatfourfromhissmallgroup,withthreemonths'supplies,shouldtravelthe1,250kilometerstothenorthcoastasquicklyaspossible.TheytoldtheotherstowaitforthematCooper'sCreek.

Thejourneyacrossthedesertwasverydifficult,butattheendofJanuary,theyreachedtheFlindersRiverneartheGulfofCarpentaria.Theystartedtheirreturnjourney,butnowitwastherainyseasonandtravelingwasslowandevenmoredifficultthanontheirtripnorth.Theydidnothaveenoughfood,andthemenbecamehungryandsick.Thenoneofthemdied.Someofthecamelsdiedorwerekilledforfood.

Finally,onApril21,theyarrivedbackatCooper'sCreek,onlytofindthatnoonewasthere.TherestoftheexpeditionhadleftthedaybeforebecausetheythoughtBurkemustbedead.Themencontinuedsouth,butwithoutenoughfood,bothBurkeandWillsdied.Aborigineshelpedthelastmanwhowasstillalive,andasearchpartyfoundhiminSeptember1861.Hewashalfcrazyfromhungerandloneliness.

Thereweremanyreasonsthattheexpeditiondidnotgoasplanned.Ithadaninexperiencedleader,themenmadebaddecisions,somedidnotfolloworders,andtheydidnotgetalong.ButitwasthefirstexpeditiontocrossAustralia,andBurkeandWillsarestillknownasheroesofexploration.

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2AlexandraDavid-Neel:AFrenchWomaninTibet

Tibethasbeenasecretandmysteriousplacetotherestoftheworldforseveralcenturies.ItisonahighplateauinAsia,surroundedbyevenhighermountains,andonlyafewforeignerswereabletocrossitsbordersuntilrecently.

OneoftheseforeignerswasaFrenchwomannamedAlexandraDavid-Neel(1868-1969).ShetraveledbyherselfinIndiaandChina.ShestudiedtheBuddhistreligion,wrotearticlesandbooksaboutit,andcollectedancientBuddhistbooks.ShealsobecameaBuddhistherself.

David-Neelalwayssaidshehadanunhappychildhood.Sheescapedherunhappinessbyreadingbooksonadventureandtravel.SheranawayfromschoolseveraltimesandevenranawaytoEnglandwhenshewasonly16.

Shewasasingerforseveralyears,butin1903shestartedworkingasajournalist,writingarticlesaboutAsiaandBuddhismforEnglishandFrenchmagazinesandnewspapers.Thenextyear,whenshewas37,shemarriedPhilippe-FrancoisNeel.Itwasanunusualmarriage.Afterfivedaystogether,theymovedtodifferentcitiesandneverlivedtogetheragain.Yethesupportedherallhislife,andshewrotehimhundredsoflonglettersfullofdetailsabouthertravels.

ShetraveledalloverEuropeandNorthAfrica,butshewenttoIndiain1911tostudyBuddhism,andthenherrealtravelsbegan.ShetraveledinIndiaandalsoinNepalandSikkim,thesmallcountriesnorthofIndiaintheHimalayaMountains,buthergoalwasTibet.ShecontinuedtostudyBuddhismandlearnedtospeakTibetan.Shetraveledtovillagesandreligiouscenters,withonlyaninterpreterandafewmentocarryhercampingequipment.Forseveralmonths,shelivedinacaveinSikkimandstudiedBuddhismandtheTibetanlanguage.Thensheadopteda15-year-oldSikkimeseboytotravelwithher.Heremainedwithheruntilhisdeathattheageof55.

Forthenextsevenyears,shetraveledinremoteareasofChina.ThesewereyearsofcivilwarinChina,andshewasoftenindanger.Shetraveledforthousandsofkilometersonhorsebackwithonlyafewmentohelpher—throughdesertheatandsandstormsandtherain,snow,andfreezingtemperaturesofthecolderareas.

In1924,David-Neelwas56yearsold.Shedarkenedherskinanddressedasanoldbeggar.Shecarriedonlyabeggar'sbowlandabackpackandtraveledthroughhotlowlandsandsnowymountainpassesuntilshereachedTibet.BecauseshespokeTibetansowell,shewasabletoreachthefamouscityofLhasawithoutanyoneknowingthatshewasEuropeanandforbiddentobethere.Itwasoftenfreezingcold,andsometimestherewasn'tenoughfood.Sometimesshewassick,andonceshenearlydied.Thiswasthemostdangerousofallherjourneys,butshereachedhergoalandcollectedmoreinformationaboutTibetanBuddhism.

ShereturnedtoFrancein1925.ShespentseveralyearswritingaboutherresearchandadventuresandtranslatingancientTibetanreligiousbooks.Whenshewas66,shereturnedtoChinafortenyears.In1944,theSecondWorldWarreachedeventhatremotearea,andattheageof76,shewalkedfordays,sometimeswithoutfood,untilshewasabletoreachaplacefromwhichshecouldflytoIndiaandthenhometoFrance.Shecontinuedwritingandtranslatinguntilshedied,justsevenweeksbeforeher101stbirthday.

Mostexplorerstraveledtodiscoverandmapnewplaces.David-NeelwenttodoresearchonBuddhism.Shesaidthatfreedomwasthemostimportantthinginlifeforher,and,likemanyotherexplorers,shelivedadangerous,exciting,freelife.

(633words)

3VitusBering:AcrossSiberiatoNorthAmerica

In1733themostcompletescientificexpeditioninhistoryuptothattimeleftSt.Petersburg,Russia.ThegoaloftheexpeditionwastoexploretheeastcoastofSiberiaandtofindoutifAsiaandNorthAmericawerejoined.Thescientistsplannedtoreportoneverything:thegeographyclimate,plants,animals,andcustomsandlanguagesoftheSiberianpeople.

TheexpeditionhadtocrossSiberiainordertoreachthePacificOcean.VitusBering,theleaderofthewholeexpedition,leftSt.Petersburgwithalmost600people.Thegroupincludedafewscientists,skilledworkersofallkinds,soldiers,andsailors.AlexeiChirikovleftlater,withmostofthescientistsandtonsofsupplies.

IttooksevenyearsforBering'sandChirikov'sgroupstocrossSiberia.Theytraveledmostlyinflat-bottomedboatsontherivers.Bering'sgroupspentayearinTobolsk,wheretheybuiltashipandexploredtheObRiver.TheycontinuedtoYakutsk,wheretheyspentfouryears.Yakutskwasonlyasmallvillageandthereweremampeopleintheexpedition,sotheyhadtobuildtheirownbuildings.TheyalsobuiltboatsandexploredtheLenaRiver.ThentheymovedontoOkhotskontheeasterncoast.Ittooktwomoreyearstobuildshipssothattheycouldexploreandmaptheeastcoast.

Beringmadecarefulplans,buttherewerealwaysproblems.Forexample,theylostalotoftheirfoodwhenoneoftheshipssankinastorm.Butfinally,theirtwoshipsstartedforNorthAmerica.Theyhadonlyonesummerinsteadoftwoyearsfortheirexplorationsbecauseofthemanyproblemsanddelays.Andsummersareshortinthenorth.

Therewasmorebadluck.Therewerestorms,andthetwoshipslostcontact,butatlastthesailorsonBeringshipsawmountainsashortdistanceacrossthesea.ThisprovedthatNorthAmericaandAsiaweretwoseparatecontinents.

Theirproblemscontinued.Theirwatersupplywaslow,butwhenthemenwentashoreinAlaska,theygotwaterthatwasalittlesalty.Manyofthemenweresickfromscurvy,adiseasecausedbythelackofvitaminC.Whentheydrankthesaltywater,theybecameevensicker.Thentheystarteddying,oneafteranother.

Astheshipsailedsouth,backtowardOkhotsk,itbecamelostinstorms.Finally,astormdroveitontoasmallislandandthemenknewtheirshipcouldnotsailagain.Theywereinaplacewithnotrees,buttherewerebirdsandanimalsforfood,andfreshwatertodrink.However,itwastoolateformanyofthem.Mencontinuedtodiefromscurvy,andonDecember8,1741,Beringdiedandwasburiedontheislandthatisnownamedforhim.Whenspringcame,thefewremainingmenwereabletobuildasmallshipfromthewoodintheoldoneandleavetheisland.

Bythistime,theRussiangovernmenthadlostinterestintheNorthPacific.Bering'sreportsweresentbacktoSt.Petersburgandforgotten.Decadeslater,peoplerealizedthatBeringwasagreatexplorer.HisexpeditiongatheredimportantscientificinformationabouttheinteriorofSiberia,mademapsoftheeasterncoast,anddiscoveredanewpartofNorthAmerica.Today,wehavetheBeringSeabetweenSiberiaandAlaskatoremindusoftheleaderofthisgreatscientificexpedition.(581words)

4RobertScott:ARacetotheSouthPole

ThefirstpersontoreachtheSouthPolewasRoaldAmundsen,aNorwegian.

RobertScott,whowasEnglisharrivedattheSouthPoleamonthafterAmundsenanddiedonthereturnjourneytohisship.Yet,strangelyenough,Scottbecameahero,butAmundsendidnot.

CaptainRobertScott(1868-1912)wasanofficerintheEnglishnavy.From1901to1904,heledanexpeditiontoAntarcticaforaBritishscientificorganizationcalledtheRoyalGeographicalSociety.Hisgrouptraveledfarthersouththananyoneelsehadeverdone.Hegatheredinformationonrocks,weather,andclimate,andhemademaps.WhenhereturnedtoEngland,hewasanationalhero.

AfewyearslaterScottdecidedtoorganizeanotherexpedition.HesaidthathewantedtomakeacompletescientificstudyofAntarctica,buthisrealgoalwastobethefirstpersonattheSouthPole.Hetookthreedoctors,severalscientists,andanumberofothermenwithhim.

Scott'sgroupsailedonashipnamedtheTerraNovainJune1910.WhentheyreachedAustralia,theylearnedthatAmundsenwasalsoonhiswaytothePole.

AmundsenandScottwereverydifferentfromeachother,andtheymadeverydifferentplans.Amundsenplannedeverythingverycarefully.Hetooksledsanddogteams,asthegreatArcticexplorersdid.Scotttookponies(smallhorses)andafewdogs,butheplannedtohavehismenpullthesledsthemselvesformostofthetrip.

Onearlierexpeditions,assomedogsbecameweak,themenkilledthemforfoodforthemselvesandtheotherdogs.Amundsendidthistoo,andithelpedhimreachthePole,butlaterpeoplecalledhim"dogeater."Scottwouldnoteathisdogs,andthiswasonereasonhediedonthisexpedition.

Therewereotherdifferencesbetweenthetwoexpeditions.Amundsensailed100kilometersclosertothePolethanScottdid.Scottalsohadthebadluckofhavingextremelybadweather—daysofblizzardsandstrongwinds.Itwasoften-40C(minus40degreesCelsius).

Scottandhismenbuiltabasecampneartheocean'sedgeandspentthewinterthere.TheyusedsledsandponiestocarryatonofsuppliesfartherinlandtoaplacethattheynamedtheOneTonDepot.Whenspringcame,afewofthemenstartedaheadoftheotherswithmotorizedsledstoleavesuppliesalongtheway.However,afteronlyafewdays,themotorizedsledsbrokedown,andthemenhadtopullthem.

Afewdayslater,ScottstartedfortheSouthPolewithafewmen.Thewholejourneywasverydifficult.Scottandhismeneitherwalkedthroughdeepsnoworskiedovericeandunevenground.Theclimatewastoodifficultfortheponies,andtheyalldied.Therewerefrequentsnowstorms.Sometimesthemencouldn'tleavetheirtentsforseveraldaysbecauseofblizzards.

WhenScottwas260kilometersfromthePolo,hesentallbutfourbacktothebasecamp.Thiswasprobablyhismostseriousmistake.Histentwasbigenoughforonlyfourpeople,andhehadonlyenoughfoodandfueltortour.Somehowhehadtoprovideforfourpeopleplushimself.Also,onemanhadlefthisskisbehindwithsomeofthesupplies.Hehadtowalkinthesnowandthissloweddownthewholegroup.

OnJanuary17,1912,ScottandhismenreachedthePole,onlytofindatentandtheNorwegianflag.TheywerenotthefirstpeopletoreachtheSouthPole.Theyhadlosttherace.

Thenextday,theystartedthe1,300-kilometerjourneybacktotheirbasecamp,pullingtheirheavysledsfullofsupplies.ThetripbackwasworsethanthetriptothePole.Theybecameweakfromhunger.Attimes,thewhitenesseverywheremadethemblind.Theirfingersandtoesbegantofreeze,andtwoofthemenfellandinjuredthemselves.Theydidn'thaveenoughfueltokeepwarmintheirtent.Theybecameexhaustedandhadmoreandmoredifficultypullingtheirsleds.

Finally,onemandied.Thenanotherbecamesoweakthatheknewhewasendangeringthelivesoftheothers.Onenight,heleftthetentandneverreturned.Hewalkedoutintotheblizzardtodieinsteadofholdingbacktheotherthree.

Everyday,Scottdescribedtheterriblejourneyinhisdiary.OnMarch21,thethreeremainingmenwereonlytwentykilometersfromtheOneTonDepot,butanotherblizzardkeptthemintheirtent.OnMarch29,theywerestillunabletoleavetheirtent.Onthatday,Scottwrotehislastwordsinhisdiary.

Asearchpartyfoundthethreebodieseightmonthslater.TheyalsofoundScott'sdiary,excellentphotographsoftheexpedition,andletterstotakebacktoEngland.

Thesearchpartyleftthefrozenbodieswheretheyfoundthem.

Today,thebasecampbuildingisstillthere.Insidearesupplies,furniture,andthemen'sbelongings.TheyhavebeenleftjustthewaytheywerewhenScott'sexpeditionwasthere.NewZealandtakescareofthebuildinganditscontents.

RobertScott'snamelivesoninstoriesofhistriptoAntarctica,thelastpartoftheEarththatpeopleexplored.HewasnotthefirsttoreachtheSouthPole,butheisrememberedasoneofthegreatheroesofexploration.

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5IntotheDeep:OceanExploration

Saltwatercoversroughly71%oftheEarth'ssurface,andyetwehavespentmuchmoretimeexploringtheEarth'smountains,forests,anddesertsthanstudyingitsoceans.Scientistssaythatweknowmoreaboutthemoonthanweknowaboutourownoceans.Andtoday,wecontinuetospendmoremoneyonspaceexplorationthanonoceanexploration.

Whyisitthatweknowsolittleabouttheoceansthatsurroundus?Perhapsitisbecause,forcenturies,peoplethoughtoftheoceanasjustatravelnetwork.Itwasawaytogetfromoneplacetoanother.Mostoceantravelersstayedclosetothecoast.Theirgoalwasnottoexploretheoceanbutrathertofindnewtraderoutesfortheexchangeofspicesandothergoods.

Toearlysailors,theoceanwasalsoafrighteningplace,fullofdangerouscreatures.Theythoughtthat,deepbelow,theoceanwasadarkandlifelessplace.Believingthispeoplehadlittleincentivetoexploretheoceandepths.

Oceanexplorationwasalsohamperedbytheconditionsbelowthesurface.Thetremendouspressureofthewaterwouldcrushanunprotecteddiver.Watertemperatureontheoceanfloorwasnotinvitingeither.Vents,oropenings,ontheoceanfloorhavetemperaturesashighas254°F(254degreesFahrenheit)or123°C(123degreesCelsius).

Toexplorebelowthesurfaceoftheocean,humansneededspecialequipment.

Earlydivingsuitsfromthelateeighteenthcenturyandearlynineteenthcenturywerenotveryuseful.Onetypeenclosedthediver'sbodyinacylinder,makingitdifficulttomovearound.Alatertypeofdivingsuitreplacedthelargecylinderwithaheavymetalhelmet.Airfromabovethesurfacetraveledthroughatubeintothehelmet.

Theseearlydivingsuitsallowedpeopletodescendfiftyfeetbelowtheoceansurfaceforaboutanhour.

In1872,thefirstshipequippedforoceanexplorationsetoutonafour-yeartriparoundtheworld.Theshiphadtwolaboratories,anditcarriedthemostadvancedscientificequipmentofthetime.Scientistsontheshiptestedthetemperatureanddensityofseawater.Theygatheredinformationaboutoceancurrentsandmeteorology.Theydiscoveredanunderwatermountainchainandmorethan4,000newspecies.Theresultsofthisexpeditionencouragedinterestinexploringfartherbelowtheoceansurface.Todothis,however,diversneededbetterequipmenttoprotectthemfromthepressureofwater.

Twodivers,CharlesBeebeandOtisBarton,designedoneoftheearlysubmersiblesfordeep-seadiving.Itwasalarge,hollow,steelballlessthanfivefeetindiameterandweighing5,000pounds.Alongheavychainconnectedthesteelbailtoashipabove.In1934,BeebeandBartondescendedhalfamilebelowthesurfaceoftheoceanintheirsubmersible.Frominsidethesteelball,theywereabletoseeextraordinarycreatures.Thiswasagreatbreakthroughforoceanexploration,fornowpeoplecouldseetheunderwaterworldwiththeirowneyes.

SinceBeebeandBartonsrecord-breakingdescent,improvementshavebeenmadeindivinequipment,allowingpeopletotraveldeeperforlongeramountsoftime.

Justtwenty-sixyearsafterBeebeandBarton,shalf-miledescent,JacquesPiccardandotherstraveletoadepthof35,797feet,ornearlysevenmiles,intheirownmuchimprovedsubmersiblecalledtheTrieste.Evenatthisgreatdepth,theexplorersdiscovereddeep-seandnewspecies.

Theworkofdeep-seaexplorershasgivenusapictureoflifefarbelowthesurface.Tnowgreaterunderstandingofthediversityoflifeintheocean.Wearenowmoreawareofdependenceonhealthyoceans.Stilllessthanonetenthof1%ofthedeepoceanhasbeenexplored.SylviaEarle,oneoftheleadingexpertsonoceans,says,"We'reinanewcenturnewmillennium,andmostoftheplanethasyettobeseen."

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6WorldPopulationGrowth

Forthousandsofyears,thepopulationoftheworldincreasedgradually.Then,inthemidnineteenthcentury,theworld'spopulationstartedtoincreaserapidly.Inthe100yearsbetween1830and1930,thepopulationoftheworldgrewfrom1billionto2billionpeople.By1960,justthirtyyearslater,theworld'spopulationhadhit3billion.Fifteenyearslater,thepopulationreached4billion.Then,justelevenyearslater,therewere5billionpeopleonEarth.In1999,wepassedthe6billionmark.

Today,theworld'spopulationgrowsby76millionpeopleeveryyear.Thatisabout240,000peopleeveryday.Bytheyear2050,researcherspredictthatthepopulationoftheworldwillbe9.1billion.

DoestheEarthhavethenaturalresourcestosupportthismanypeople?

Unfortunately,theanswertothisquestiondependsoninformationwedon'thave.Forexample,wedon'tknowhowpeoplewillchoosetoliveinthefuture.Wedon'tknowwhattheirstandardoflivingwillbe.Wealsodon'tknowwhatnewtechnologieswillbeavailableinthefuture.

WedoknowthattheEarth'snaturalresourcesarelimited.Freshwater,forexample,iscrucialforhealthandfoodproduction.However,morethan97%ofthewateronEarthissaltwater,whichispoisonoustobothpeopleandcrops.Only3%ofthewateronEarthisfreshwater,andthreequartersofthatfreshwaterisfrozenattheNorthandSouthPoles.Today,thedemandforfreshwaterisgreaterthanthesupplyinroughlyeightycountriesaroundtheworld.By2025,scientistspredictthatforty-eightcountrieswillhavechronicshortagesofwater.Atpresent,desalinization,ortheremovalofsaltfromsaltwater,isnotasolutiontotheshortageoffreshwater.Ittakesalotofenergytoremovethesaltfromoceanwater,andthatmakesthedesalinizationprocessveryexpensive.

Theamountoflandwecanusetoproducefoodisalsolimited.Today,roughly11%ofthelandonEarthcanbeusedforcrops,whileanother20%isavailableforraisinganimals.Eachyear,however,moreofthislandislostascitiesgrowandroadsstretchacrosstheland.Inaddition,overcultivationhasalreadydamagedanamountoffarmlandequaltothesizeoftheUnitedStatesandCanadacombined.Itispossibletoincreasetheamountoffarmland,butonlyalittle.Somefarmlandcanbemoreproductiveifpeoplestartusingdifferentfarmingmethods,butthiswillnotincreaseworldwideproductionverymuch.

Cleanairisanotherimportantnaturalresource.However,ittooisthreatenedbythegrowingpopulation.Theaveragepersontodayputsabout1.1metrictonsofcarbonintotheatmosphereeachyear.Mostofitcomesfromburningfossilfuels——gasoline,coal,oil,woodandnaturalgas.Scientistssaythattheamountofcarbondioxideintheairisalready18%higherthanitwasin1960.Whateffectwould3billionmorepeoplehaveontheairwebreathe?

Whilewehavemanydifferentsourcesofcommercialenergythereisalimitedsupplyofmanyofthem.Todaymostoftheworld'scommercialenergycomesfromthreenonrenewableenergyresources—petroleum,naturalgas,andcoal.Threequartersofthiscommercialenergyisusedbydevelopedcountries.Asthestandardoflivinggoesupinothercountries,sowillthedemandforenergy.SomescientistspredictthatifeveryoneintheworldlivedlikeanAmerican,ourfossilfuelsupplywouldlastforjustfifteenmoreyears.

Clearly,thenumberofpeoplethattheEarthcansupportinthefuturewilldependonmanythings.TheEarthmaybeabletosupport9billionpeople,butwhatwilltheirstandardoflivingbe?Andwhateffectwillallthesepeoplehaveontheenvironment?

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7ChangesintheFamily

BarbaraTodisco,35,andherhusband,Ted,37,havetwochildren.Theylivetogetherinwhatiscalledanuclearfamily.Anuclearfamilyconsistsoftwogenerations——twoparentsandtheirchildren.

EsmeTanguay,43,liveswithherdaughter,Maria,11.Theylivetogetherinasingle-parentfamily.IntheUnitedStates,aquarterofAmericanchildrennowgrowupinsingle-parentfamilies.

JuanDiego,45,ofMiami,Florida,hastwochildrenfromhisfirstmarriage.Hissecondwife,Nancy,hastwochildrenfromherfirstmarriage.JuanandNancyalsohaveachildtogether.JuanandNancyandthefivechildrenlivetogetherinwhatisnowcalledablendedfamilyCarlJacobs,32,liveswithhiswife,theirtwochildren,andhiswife'smotherandfather.Theyareanextendedfamily.Extendedfamiliesconsistofmorethanonesetofparentsandchildren.Themostcommontypeofextendedfamilyconsistsofamarriedcoupleandoneormoreoftheirmarriedchildrenalllivingtogetheronehousehold.Anextendedfamilymightalsoconsistoftwobrothersandtheirwivesandchildren.Alargeextendedfamilymightconsistofgrandparents,parents,children,uncles,andotherrelatives.

Forcenturies,theextendedfamilywasthemostcommontypeoffamily.Onebenefitoflivinginanextendedfamilyisthattherearemorepeopletosharethework.Thiswasespeciallyimportantinsocietieswheremothershadtoworkoutsidethehome,raisingcropsorgatheringfood.Inanextendedfamily,motherscouldworkoutsidethehomewhileotherfamilymemberswereavailabletotakecareofthechildrenanddootherhouseholdtasks.

IntheUnitedStates,oneofthebiggestchangesinfamiliesinthelastcenturyhasbeenadecreaseinthenumberofextendedfamilies.Oneveryimportantreasonforthisdecreasewasindustrialization.Thegrowthofindustrymadeitpossibleformanyyoungpeopletoleavetheirfamiliesandmovetothecitytoworkinfactories.Bythe1920s,amajorityofchildrenintheUnitedStateswerenolongerlivinginextendedfamilies.Instead,theywerelivinginfamilieswithafatherwhowenttoworkandamotherwhostayedathome.

Aslongasafamilycouldaffordtohavethemotherstayathome,thistypeoffamilywasabletosurvive.Formanyfamilies,however,thiswasnotfinanciallypossible.AsthecostoflivingroseintheUnitedStates,moreandmorewomenneededtoworkoutsidethehome.Atthesametime,anemphasisonequalityformenandwomenopenedthedoortonewjobopportunitiesforwomen.Beforelong,single-parentfamilies,blendedfamilies,andevenextendedfamilieswerebecomingmorecommon.

Since1970,thenumberofsingle-parentfamiliesintheUnitedStateshasincreasedtremendously.Today,thereareroughly90millionsingle-parentfamilieswithchildrenundertheageof18.Thatisa200%increasesince1970.Nearly99%ofthesesingle-parentfamiliesareheadedbywomen.Manysociologistshavestudiedsingle-parentfamiliestofindoutwhytheyareincreasinginnumber.ThefactthatitisnoweasiertogetadivorceintheUnitedStatesdoesnotfullyexplainthisincrease.

Inmanycountries,divorceratesstabilizedinthe1980sbutthenumberofsingle-parentfamiliescontinuedtoincrease.Inordertogetabetterexplanationfortheincreaseinthenumberofsingle-parentfamilies,itisalsonecessarytolookatwhypeoplearen'tremarryingandwhytherearemorebirthsoutsideofmarriagetoday.

Thesetwofactorsarealsocontributingtotheriseinthenumberofsingle-parentfamilies.

BoutrosBoutros-Ghali,theformerSecretary-GeneraloftheUnitedNations,oncesaidthatfamilies"areattheleadingedgeofchangeandareadaptingtoseriouschallenges,oftenunderverydemandingconditions."Thetruthisthatfamilieshavealwayshadtochangeandadapt,butsomehowthefamilyhasalwayssurvived.

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