This document summarizes key points from the book "Worlds within Words" by K. David Harrison about the complexity of human languages. It discusses how language change occurs naturally over time without central authority. It also examines arguments about whether all languages are equally complex and explores examples of complex linguistic structures from smaller and endangered languages, including morphemes adding smell descriptions in Siberian Tofa, onomatopoeic sound words in Tuvan, word reduplication in Rotokas and Filipino, noun classifiers in an unnamed language, and gender-specific terms and sign languages.