In Britain, the government has okayed scientists creating babies in test tubes using genetic material from three people:

Experts say three-person IVF could eliminate debilitating and potentially fatal mitochondrial diseases that are passed on from mother to child.

Opponents say it is unethical and could set the UK on a “slippery slope”.

They also argue that affected couples could adopt or use egg donors instead.

Mitochondria are the tiny, biological “power stations” that give the body energy. They are passed from a mother, through the egg, to her child.

Defective mitochondria affect one in every 6,500 babies. This can leave them starved of energy, resulting in muscle weakness, blindness, heart failure and death in the most extreme cases.

The BBC says: “It is a change that would have ramifications through the generations as scientists would be altering human genetic inheritance.” There have been critics:

Dr David King, the director of Human Genetics Alert, said: “These techniques are unnecessary and unsafe and were in fact rejected by the majority of consultation responses.

“It is a disaster that the decision to cross the line that will eventually lead to a eugenic designer baby market should be taken on the basis of an utterly biased and inadequate consultation.”

One of the main concerns raised in the HFEA’s public consultation was of a “slippery slope” which could lead to other forms of genetic modification.

So: to relieve the undeniable and cruel suffering of a small number of babies born with this disease, and the handful of families who might benefit from this therapy, we cross a massive ethical line into engineering babies who have more than two biological parents.

To accommodate a tiny minority, we cast aside bedrock constraints based on an enduring understanding of human nature. Because that’s how we roll in modernity. There is no line we will not cross. If it can be done, it will be done. That is the ultimate lesson in human nature, I suppose.