Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Sentence1: Macroevolution is more than repeated rounds of microevolution. 
Sentence2: evolution over geologic time above the level of the species is more than repeated rounds of microevolution.
microevolution

Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.
Mammals

Sentence1: Scientists still know relatively little about Archaea. 
Sentence2: People that do research still know relatively little about Archaea.

Archaea