Whenscientistssetouttoexploretherootsofhumanlaughtersomeapes（类人猿）werejusttickled（胳肢）tohelp.That’showresearchersmadeavarietyofapesandsomehumanbabieslaugh.Afteranalyzingthesoundstheyconcludedthatpeopleandgreatapesinheritedlaughterfromasharedancestorthatlivedmorethan10millionyearsago.Expertspraisedtheworkitgivesstrongevidencethatapelaughterandhumanlaughterarerelatedthroughevolution（进化）.

Scientistshavenotedthatapesmakecharacteristicsoundsduringplayorwhilebeingtickledespeciallytosignalthatthey’reinterestedinplaying.It’sbeensuggestedbeforethathumanlaughtergrewoutofprimate（灵长类动物）roots.Butapelaughterdoesn’tsoundlikehumanlaughter.Itmaybeslowernoisybreathing.Sowhatdoesthathavetodowiththehumanha-ha?ToinvestigatethatMarinaDavilaRossandhercolleaguescarriedoutadetailedanalysisofthesoundsmadebyticklingthreehumanbabiesand21otherprimatesapesincluded.

Aftermeasuring11featuresinthesoundfromeachspeciestheytriedtofindouthowthesesoundsappearedtoberelatedtoeachother.Theresultlookedlikeafamilytree.SignificantlythattreematchedthewaythespeciesthemselvesarerelatedthescientistsreportedonlineinthejournalCurrentBiology.Theyalsoconcludedthatwhilehumanlaughtersoundsmuchdifferentfromapelaughtertheirtypicalfeaturescouldhavecomefromthesameancestor.

Pankseppwhostudieslaughter-likeresponsesinanimalsbutdidn’tparticipateinthenewworkcalledthepaperexciting.Panksepp’sownworkconcludesthatevenratsproducelaughterinresponsetoplayingandticklingwithsoundsthatcanhardlybeheardbypeople.RobertProvineascientistwhowrotethebookLaughter:AScientificInvestigationsaidthenewpapershowedsomeimportantclueslikeapesoundsthathadn’tbeenrealizedbefore.

69.Whydidthescientistsanalyzethelaughtermadebyticklinghumanbabiesandapes?

A.Totrytodiscoveriftheycanmakecharacteristicsounds.

B.Toseeiftheyinterestedinplaying.

C.Tofindoutifthelaughterofapesandhumansisrelated.

D.Tofindoutthedifferencesbetweenhumansandapes.

70.BasedonParagraph3wecanknowthatresearchers