The branches · 6 of 7
Inheritance
What we pass to our children, chosen rather than left to chance.
Changes made before birth that a child carries for life and may pass on: editing the genes of an embryo, choosing among embryos, and whatever comes after. This is the one branch where the person changed could not consent, which is why the record here is watched most closely.
4 upgrades
furthest stage reached: in clinical use- A baby is born with donor mitochondria to avoid an inherited disease
Mitochondria, the parts of a cell that make its energy, carry a little DNA of their own, passed only from mother to child; faults in it cause diseases that are often fatal in childhood. Moving the nucleus of the mother's egg into a donor's egg with healthy mitochondria gives a child that is genetically the parents' with a small part from a third person. The first such child was born in 2016, in Mexico, to avoid a rule elsewhere; Britain had already made it lawful under licence, and eight children born there were reported in 2025. It is the only change to inheritance a regulator has approved.
- Embryos are chosen by a genetic score for traits, not disease
Fertility clinics have long tested embryos for single-gene diseases. Since 2019 companies have sold scores that add up thousands of small genetic differences to rank embryos by their risk of common diseases, and since 2025 two have sold rankings for traits that are not diseases at all: predicted height, predicted intelligence, eye colour. No regulator reviews these scores, the predictions are weak at the level of one embryo, and the practice is condemned by most of the field. It is on the tree because it is being done, to paying customers, through named clinics.
- A child is born from an embryo whose genes were edited on purpose
The genes of a human embryo are changed before it is implanted, and a child is born carrying the change in every cell, able to pass it on. This happened in China in 2018, against the rules of the field and the law: twin girls, then a third child, with a gene disabled in the hope of making them resistant to HIV. The scientist responsible announced it himself and went to prison for it. The record keeps the entry at the stage it reached, because the ladder records what has happened, not whether it was allowed.
- A mammal is carried to birth in an artificial womb
The end point of taking birth out of the body: an animal that goes from a fertilised egg to a live birth with no mother at any stage. Nothing has done this. The two famous results are halves: in 2017 lambs taken from their mothers two thirds of the way through pregnancy lived for four weeks in a fluid-filled bag and were born from it; in 2021 mouse embryos grew in bottles from a few days old to about the midpoint of pregnancy. The gap between the two halves has not been bridged in any mammal, which is why this entry sits at the bottom of the ladder with a precise test.