Fig. 4

Polymorphisms in language evolution. a Synonymy: languages have many nearly synonymous words (German Hals and Nacken both mean ‘neck’ in English). They can be interchangeably used to express one and the same concept. Near synonymy is often resolved by dropping one of the two words. b Analogy: languages with complex morphology (case systems, etc.) often have irregular paradigms which consist of different stems (like good, better, best in English). These paradigms are often resolved retaining only one form and adapting the other forms to this model (e.g., good, gooder, goodest). b Derivation: words can be slightly modified by adding affixes (word derivation) or merging to words with each other (compounding). Often, both the modified or merged forms can still be interchangeably used with the original forms. They can also replace the original forms. d Incomplete lineage sorting: if rapid divergence occurs before the polymorphisms are resolved, they may yield patterns that seem to be in contradiction with tree-like divergence