Abstract:Anchored on linguistic innateness, Principle and Parameter (PP) Theory assumes Universal Grammar is composed of some principles or isomorphic biological structures, which extensively enhances researches in language acquisition, cross-language comparison, and language change.Based on current biolinguistics, the paper argues that PP Theory essentially misinterprets linguistic phonotype as linguistic genotype, and transforms problems of cross-language variations to typology derivations in formal method, failing to meet the requirements of explanatory adequacy and biological adequacy, and to explain language origin and evolution.Merger without cross-language variation is a biological design of language, and morphogenesis, a dynamic interaction between endogenous mechanism and epigenetic system, results in cross-language variations as post-syntax, which also explains the problems of the universal nature of genotype, ecological variation of phenotypes, and factors leading to such variations.