It was heartening to read Professor Hugh McLachlan's letter (Emotional squeamishness over deaf baby, March 14) on the positive moral aspect of a deaf couple's request to choose an embryo destined to lead to the birth of a deaf child. Having mulled over the possibilities thrown up by embryo selection and the ethical dilemmas involved, my mind is made up to select, with my partner, only embryos destined to give rise to tall, intelligent, strong, blond and blue-eyed children - some readers might think this sounds familiar.

Consider an analogy: suppose, in a loch, several children are drowning and no-one is around to save them. One of the children has been born taller, stronger and more intelligent than the others (by my selection process) and manages to stay afloat, making it to the safety of land. None of the children had a stronger moral or legal claim to survive than the others. None had a positive moral or legal right to survive.

If I choose an embryo destined to have certain physical characteristics enabling survival under such circumstances, I would be doing nothing wrong - morally permissible.

Readers should note that the Darwinian term "fitness", in terms of survival, has nothing to do with physical size or strength, as is sometimes erroneously believed. It is much more complex, a bit like using morals as a justification for some things.

As for the people wanting to select for a deaf child, let them go ahead, but they might not get any great thanks from the offspring - only doing the experiment would give the answer in 10-20 years once the child has grasped the full import of what was chosen for it.

Dr Ronnie Gallagher, Edinburgh.

The comments made by Professor Hugh McLachlan simply do not stand up to scrutiny. His first argument is that it would not be wrong to choose a deaf baby that would otherwise not have been born. This fails on a number of points. First, it strikes me that a great number of babies would not have been born had their parents not had sex leading to their conception. However, this does not mean that the parents would have the right to ensure that their child's biology matches their own, simply because they ensured the child's birth. If a heroin addict became pregnant tomorrow, health services would do everything in their power to ensure that the child was not born addicted to heroin.

I am not, before I am beset by accusations, comparing deaf people to heroin addicts. I am comparing two conditions dangerous to the human body. Human beings evolved to have their level of hearing for many reasons, not least of which is safety. Noise can alert us to many dangers, from the sound of oncoming traffic to the yell of a passer-by if we do not notice we are in trouble. That is to say nothing of the cry of a child in distress. I defy anyone reading this correspondence to tell me that those who are deaf are not more at risk in the world than those with the full range of hearing.

Also, Professor McLachlan's analogy grants the status of a living child to an embryo. Not to choose an embryo which contains a gene that could cause the child to be deaf is not to kill a child, it is deciding that any child that is born will not be born deaf. This lapse in the labelling of an embryo as a child is also apparent in his "drowning children" story. Embryos that are not used are far from being dead children, and to liken them to drowning children who are not "saved" is preposterous.

It is the duty of a parent to ensure their child's safety. By ensuring a child will be born deaf, you are placing it in danger. While I sympathise with wanting to be close to your child and share with it your experiences, this should not be done at the cost of the child's safety.

Stephen Sutherland, Port Glasgow.