Complex sentence: The field of study of sexuality in non-human species has been a long standing taboo, with researchers either failing to observe or mis-categorizing and mis-describing sexual behaviour which does not meet their preconceptions.
Split into simpler sentences: The field of study of sexuality in non-human species was a long standing taboo. In the past, researchers sometimes failed to observe, mis-categorizing and mis-described sexual behaviour which did not meet their preconceptions.