25 Amazing Facts About the Human Body - Mental Floss

25 Amazing Facts About the Human Body ; Wisdom teeth serve no purpose. They're left ... Thehumanbodyisanamazingpieceofmachinery—withafewweirdquirks. It’spossibletobrushyourteethtooaggressively.Doingsocanweardownenamelandmaketeethsensitivetohotandcoldfoods. Goosebumpsevolvedtomakeourancestors’hairstandup,makingthemappearmorethreateningtopredators. iStock.com/MyetEckWisdomteethservenopurpose.They’releftoverfromhundredsofthousandsofyearsago.Asearlyhumans’brainsgrewbigger,itreducedspaceinthemouth,crowdingoutthisthirdsetofmolars.Scientistsaren'texactlysurewhyweyawn,butitmayhelpregulatebodytemperature.Yourfingernailsdon’tactuallygrowafteryou’redead.Iftheywerelaidendtoend,allofthebloodvesselsinthehumanbodywouldencircletheEarthfourtimes.Humansaretheonlyanimalswithchins.iStock.com/mhelm3011Asyoubreathe,mostoftheairisgoinginandoutofonenostril.Everyfewhours,theworkloadshiftstotheothernostril.Bloodmakesupabout8percentofyourtotalbodyweight.Thehumannosecandetectabout1trillionsmells.Youhavetwokidneys,butonlyoneisnecessarytolive.Bellybuttonsgrowspecialhairstocatchlint.iStock.com/PeopleImagesThesatisfyingsoundofcrackingyourknucklescomesfromgasbubblesburstinginyourjoints.Skinisthebody’slargestorganandcancomprise15percentofaperson’stotalweight.Thumbshavetheirownpulse.Yourtongueismadeupofeightinterwovenmuscles,similarinstructuretoanelephant’strunkoranoctopus’stentacle.Onageneticlevel,allhumanbeingsaremorethan99percentidentical.iStock.com/BorupFotoThefootisoneofthemostticklishpartsofthebody.Extraocularmusclesintheeyearethebody’sfastestmuscles.Theyallowbothofyoureyestoflickinthesamedirectioninasingle50-millisecondmovement.Asurgicalprocedurecalledaselectiveamygdalohippocampectomyremoveshalfofthebrain’samygdala—andwithit,thepatient’ssenseoffear.Thepinealgland,whichsecretesthehormonemelatonin,gotitsnamefromitsshape,whichresemblesapinenut.Hairgrowsfast—about6inchesperyear.Theonlythinginthebodythatgrowsfasterisbonemarrow.iStock.com/GlobalStock Noonereallyknowswhatfingerprintsarefor,buttheymighthelpwickwaterawayfromourhands,preventblisters,orimprovetouch. Theheartbeatsmorethan3billiontimesintheaveragehumanlifespan. Blushingiscausedbyarushofadrenaline.