Stableisotopesofmostimportantbiologicalelements,suchasC,H,NandO,affectlivingorganisms.Inrapidlygrowingspecies,deuteriumandtoalesserextentotherheavyisotopesreducethegrowthrate.Atleastfordeuteriumitisknownthatitsdepletionalsonegativelyimpactsthespeedofbiologicalprocesses.Asarule,livingorganisms'resist'changesintheirisotopicenvironment,preferringnaturalisotopicabundances.Thispreferencecouldbeduetoevolutionaryoptimization;anadditionaleffectcouldbeduetothepresenceofthe'isotopicreso-nance'.Theisotopicresonancephenomenonhasbeenlinkedtothechoiceofearliestaminoacids,andthusaffectedtheevolutionofgeneticcode.Totesttheisotopicresonancehypothesis,literaturedatawereanalyzedagainstquantitativeandqualitativepredictionsofthehypothesis.Fourstudiesprovidedfiveindependentdatasets,eachinverygoodquantitativeagreementwiththepredictions.Thus,theisotopicresonancehypothesisisnolongersimplyplausible;itcannowbedeemedlikely.Additionaltestingisneeded,however,beforefullacceptanceofthishypothesis.
