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: harming an animal species causes that animal 's population to decrease. 
Sentence2: Wild animal populations have decreased drastically, due to both hunting and loss of habitat.
animal

Sentence1: Protozoa make humans sick when they become human parasites. 
Sentence2: paramecium are single celled animals that make humans sick when they become human parasites.
become

Sentence1: sexual reproduction increases genetic diversity. 
Sentence2: All creatures procreate via sexual reproduction.

reproduction