There is much to reflect on here - the inherent viciousness of much human behaviour, coupled with a naive belief in our own 'unique specialness' and the way in which our short lifespans make it difficult for us to learn from our history or avoid the mistakes of the past;
On the part of the alien Oankali, a similar conceit is evidenced in their certainty that their assessment of genetic qualities is all that is needed to fully understand others, and a blindness to their own fatal contradictions including; perfectionism, being control freaks, and their inability to imagine themselves in the place of those others;
It challenges the commonly held ideas of 'progress' that modern/western society has about sophistication or civilisation being synonymous with 'advanced' material technology, yet the otherwise 'primitive' Oankali surf deep space, assimilate other species and strip entire planets using only a detailed genetic understanding and adaptability as well as their own version of 'Free Trade'.
Socially, the book & Xenogenesis series also reveals from the increasingly desperate reactions of the 'human resisters' just how fundamentally important children/offspring are in giving our lives purpose (a fact that is often glossed over in today's technological society, but still appreciated in several indigenous ones) There is much else here - about the nature of gender, domination, compassion, power and community - that is insightfully woven into the characters and storyline as commented on by other reviewers. But perhaps it is Butler's treatment of human and alien sexuality that is most unusual and haunting and lingers well after you finish the book/series.
Butler is an accomplished and original writer who grounds aspects of her most memorable characters and storylines on mythic African themes - the importance and interconnections between spirituality, human relationships/lineages and science - or using the scholar, Charles Finch's concept of, 'The reunification of myth & science' as a basis for the future.
My only gripe with her work is that the books are too short, and the endings often unresolved, but this is perhaps linked to her sparse prose style and wish to explore the storylines further elsewhere. Nevertheless, I thoroughly enjoy her writing, and so will you...
Also recommended: Adulthood rites, Imago, the patternist series - in fact ALL her books.