What are the motifs in Lilith's Brood by Octavia E. Butler?

The importance of family is a recurring idea. Many of the struggles that are seen in the story come from a desire to be free but the Humans are free to do almost anything they want—with the exception of having children. The Humans in the story often are seen stealing the construct children because they cannot have their own. There are Humans in the story that do not have a strong desire to have a construct child but many of the Humans in the story are so focused on being able to have children again that when the opportunity arises for them to go to Mars and have their fertility restored, they willingly take the opportunity, even though life on Mars will be very hard and the terrain must be changed to suit Human life.