universal grammar. Further, it seems to follow that creoles would share features with the languages from which they are derived, and thus look similar in terms of grammar. Many researchers of universal grammar argue against a concept of relexification, which says that a language replaces its lexicon almost entirely with that of another. This goes against universalist ideas of a universal grammar, which has an innate grammar. Criticisms Geoffrey Sampson maintains that universal grammar theories are not falsifiable and are therefore pseudoscientific. He argues that the grammatical "rules" linguists posit are simply post-hoc observations about existing languages, rather than predictions about what is possible in a language. Similarly, Jeffrey Elman argues that the unlearnability of languages assumed by universal grammar is based on a too-strict, "worst-case" model of grammar, that is not in keeping with any actual grammar. In keeping with these points, James Hurford argues that the postulate of a language acquisition device (LAD) essentially amounts to the trivial claim that languages are learnt by humans, and thus, that the LAD is less a theory than an explanandum looking for theories. Morten H. Christiansen and Nick Chater have argued that the relatively fast-changing nature of language would prevent the slower-changing genetic structures from ever catching up, undermining the possibility of a genetically hard-wired universal grammar. Instead of an innate universal grammar, they claim, "apparently arbitrary aspects of linguistic structure may result from general learning and processing biases deriving from the structure of thought processes, perceptuo-motor factors, cognitive limitations, and pragmatics". Wolfram Hinzen summarizes the most common criticisms of universal grammar: Universal grammar has no coherent formulation and is indeed unnecessary. Universal grammar is in conflict with biology: it cannot have evolved by standardly accepted neo-Darwinian evolutionary principles. There are no linguistic universals: universal grammar is refuted by abundant variation at all levels of linguistic organization, which lies at the heart of human faculty of language. In addition, it has been suggested that people learn about probabilistic patterns of word distributions in their language, rather than hard and fast rules (see Distributional hypothesis). For example, children overgeneralize the past tense marker "ed" and conjugate irregular verbs as if they were regular, producing forms like goed and eated and correct these deviancies over time. It has also been proposed that the poverty of the stimulus problem can be largely avoided, if it is assumed that children employ similarity-based generalization strategies in