The Cement Garden by my favorite author Ian McEwan.
I think this was his first novel. McEwan started his career gaining a reputation for Macabre stories which daringly explored human nature. This was certainly one of those stories.
The plot centers around a 15 year old, his attractive 17 year old sister, a 6 year old brother, and a 13 year old sister. Their father dies of a heart attack. Then their mother gets sick and eventually dies. In order to avoid being sent to an orphanage and having the family split apart, they bury the mother's body in a chest and fill it full of concrete in the cellar. They continue to live in the house together, keeping their mother's death as a secret. The 6 year old boy has a desire to become a girl so kids at school will stop picking on him. He begins to cross dress. The main character is the 15 year old who is sexually attracted to his sister whom he eventually has incestual relations with.
Some have likened it to "Lord of the Flies", but I don't thikn this was the author's intent really. But it is in part, an examination of unsupervised human behavior.
All this talk of human evolution in the new age community as if it were synonymous with our biological evolution. But send a group of infants to mars to be raised by robots and you'll have a colony of religious savages in no time.
Why did they do it? It felt good.