Lise Barnéoud's Hidden Guests shows how this fascinating new field brings with it profound implications for medicine, and even what it means to be human, finds Helen Thomson "We are composed not only of human cells and microbes but also fragments of others " My children were conceived using donated eggs, so you would be forgiven for assuming we share no genetic material. Yet science has proved this isn't entirely true. We now know that during pregnancy, fetal cells cross the placenta into the mother, embedding themselves in every organ yet studied. Likewise, maternal cells, and even those that crossed from my mum to me, can make their way into my kids. And things might get even more chimeric - I have older sisters, so their cells, having passed into my mum during their own gestation, might have then found their way into me and, in turn, into my kids.

A planet is about to be destroyed by the collapse of a binary star system in Slow Gods, Claire North's first venture into classic science fiction. It's bad luck for those living on Adjumir, which is set to be obliterated Claire North is a successful and prolific novelist, writing under three separate names, but this is their first shift into classic science fiction, i.e. a novel with spaceships in it. I loved the title of this book, Slow Gods, and I loved the cover art. All of which is to say that I went in with high hopes. It begins: "My name is Mawukana na-Vdnaze, and I am a very poor copy of myself."