As well as studying past human colonisation on Earth, Smith has published research on how humans might evolve both physically and culturally as we leave our home planet. Before anyone draws up plans for Mars colonies or multi-generational starships, Smith believes it is essential to give serious thought to having extraterrestrial children.

It may not even be possible to conceive a child in space, which would put paid to cosmic colonies straight away. Sex in space is doubtless mechanically doable, but what is less clear is whether it will result in conception. Spaceflight is proven to be bad for human health but its effect on reproductive health is not yet fully understood. The limited studies carried out so far suggest that microgravity is likely to disrupt the body’s hormones and cosmic radiation could cause damage to the developing embryo.

Japan is currently investigating one aspect of this problem on the International Space Station with the intriguingly named Space Pup experiment. This involves flying freeze-dried mouse sperm for several months at a time to study the effects of space on mammalian fertility.

However, on the surface of Mars or with artificial gravity on a starship, weightlessness, at least, is not likely to be such a problem. So let’s assume any possible medical barriers can be overcome, the question then becomes whether it is right to bring a child into the world in a Martian colony or on a starship in the depths of space. “Philosophers call this consent to risk,” explains Smith. “Is it morally acceptable to put someone else at risk without their consent? That is, to have a child in those conditions?”