1. WHY LANGUAGES DIFFER IN THE WAY THEY DO ? Traditional thinking HISTORICAL DRIFT. History separates languages in space and time. Lupyan and Dale research DEMOGRAPHIC AND SOCIAL INFLUENCE Languages may adapt their structure to the environment in which they are being learned and used.

2. THE LINGUISTIC NICHE HYPOTHESIS Languages evolve within particular socio-demographic niches Languages with most speakers and which spread in a wider area have simpler grammar. use of lexical devices. Languages spoken by few people have a more complex Grammar use of inflectional devices that afford economy of expression.

3. INTERRUPTED TRANSMISSION HYPOTHESIS Aspects of a language difficult for adults to learn will become morphologically simpler over many generations. Complex grammatical systems, while difficult for adults, may facilitate language learning in children by providing redundant information.

4. Redundancy helps early acquisition (L1) Poverty, facilitates adult acquisition (L2) Redundancy, R L, and poverty, P L, separately specify learn ability for a language comprised of infant (L1) versus adult (L2) learners. As the proportion of L2 learners increases, greatest language fitness is obtained for languages that minimize grammatical distinctions. Adult L2 learners tolerate a higher reconstruction error than infants.