A language family is a monophyletic unit; all its members derive from a common ancestor, and all descendants of that ancestor are included in the family. Thus, the term family is analogous to the biological term clade. Language families can be divided into smaller phylogenetic units, sometimes referred to as "branches" or "subfamilies" of the family; for instance, the Germanic languages are a subfamily of the Indo-European family. Subfamilies share a more recent common ancestor than the common ancestor of the larger family; Proto-Germanic, the common ancestor of the Germanic subfamily, was itself a descendant of Proto-Indo-European, the common ancestor of the Indo-European family. Within a large family, subfamilies can be identified through "shared innovations": members of a subfamily will share features that represent retentions from their more recent common ancestor, but were not present in the overall proto-language of the larger family.
a laNguAge famIly Is a monOPHylEtic UNit; AlL its members Derive froM a CommoN AncestoR, And All dEscendaNts Of tHat anCestor aRe inCluded iN thE family. thuS the TeRm FaMIly Is AnalOgous To the BiologIcal terM cladE. lANGuage familiEs Can be DiVIDeD into SmalleR pHylogeNetic uNITs, soMEtiMeS rEFeRred tO AS "brAnches" or "subfamilieS" OF the faMilY; foR instancE, the gErmanIc LaNguaGes are a sUBFAMILY of tHe inDO-eUropEan family. subfamILIes Share a moRe reCENt common AnceStor thAN tHE COmmoN anCEsToR of the largEr Family; Proto-GErManIc, the comMon anCesTor Of THe gErmAnic SubfamiLy, wAs iTsElf A dEScendaNt of pROto-iNdo-EUropeAn, THE ComMoN ancestor of The iNdO-eUroPean FAmiLy. WiThin a LArGe fAmily, SUbfAmiLiEs cAn bE idEntified tHrouGh "sharED inNovaTiOns": MembErS oF A SubFamIly WILl SHare feAtURES tHAT rePreSeNt reteNTions frOm TheIR more recent cOmMOn anCeStor, But werE not pREsent IN The ovErall Proto-lanGUage of ThE largEr fAMily.