Factors which prevent individuals from mating.
f æ k t ə ɹ z WORD_BOUNDARY w ɪ t̠ʃ WORD_BOUNDARY p ɹ ɪ v ɛ n t WORD_BOUNDARY ɪ n d ɪ v ɪ d̠ʒ uː ə l z WORD_BOUNDARY f ɹ ʌ m WORD_BOUNDARY m eɪ t ɪ ŋ WORD_BOUNDARY