Event · event
The partial-gravity programme
Human lines adapted to develop normally at 0.38 g.
Read more in Ageing slowed, not ended
Off Earth, editing is how children are fitted to their world. The partial-gravity programme of the 2100s, which let children grow up healthy at Mars's 0.38 g, has grown into routine adaptation for each world: radiation tolerance in the Belt, cold and low gravity on Titan. Almost everyone off Earth is adapted: children before birth, and most adult emigrants by gene therapy when they arrive, which helps less. The Mandate adapts by state plan; the Settlement under the rules above, so an adaptation is allowed once proven safe, and the pool pays for poorer families' children; the Open Cities and the Lines adapt without limits. Populations now differ by world as well as by bloc, and altered people find Earth hard to return to. Whether they keep full rights to migrate to Earth, the Kinship Question, came to a head in the 2450s, when the Belt's independence made it a question of citizenship; Earth decided yes, grudgingly.
Those births are possible because the partial-gravity programme of the 2100s has already adapted human lines to low gravity. On the lightest worlds, children grow up in spin nurseries (see Designed children, in Ageing slowed, not ended).
Gravity. In 2026 nobody knows how much gravity a child needs to grow up healthy, or what centuries of low gravity do to an adult. In this history the answer was engineered, not assumed. The partial-gravity programme of the 2100s adapted human lines to develop normally at Mars's 0.38 g, and Mars-born people now struggle on Earth (see Designed children, in Ageing slowed, not ended). The Moon (0.16 g), Titan (0.14 g), Callisto (0.13 g), Ganymede (0.15 g) and the Belt are too light for adaptation alone: it helps their adults, but their children are raised in rotating spin nurseries, and adults spend regular time under spin. The Belt's habitats rotate anyway; on Titan, the Moon and Jupiter's moons the nurseries are a standing running cost.