This ambiguity continues to modern times - the Vatican's 1974 Declaration on Procured Abortion specifically "leaves aside the question of the moment when the spiritual soul is infused". Last rites are not administered.In natural reproduction, there are thousands of embryos that are spontaneously aborted every day. It is for this reason that funerals for spontaneously aborted or miscarried foetuses are not routine in the church. Perhaps Hume understands the complexity and pitfalls inherent in the Vatican's approach to the subject of frozen pre-embryos - perhaps he understands better than the Vatican that the history of church teaching on the status of the early embryo speaks against claiming "personhood" for such undifferentiated early life. St Augustine said that "unformed foetuses perish like seeds which have not fructified", clearly seeing actual human life beginning at some point after the foetus has begun to grow. While Vatican officials deem the event a "prenatal massacre" and call on married women to "adopt" the orphan embryos, Hume is prepared to settle for a decent burial.

Sir: The heated rhetoric of Vatican officials about the destruction of frozen pre-embryos in Britain provides an interesting contrast with the cool acceptance of Cardinal Basil Hume. Why should members of gun clubs? Colonel MICHAEL BADGER Runcton,West Sussex. Try telling that to gay and lesbian service personnel abused and hounded from their careers by cowards and bigots they thought were comrades-in-arms Britain is, sexually, still Europe's Deep South. And just as the US Supreme Court imposed civil rights on southern rednecks, so hopefully the European Court will demand that our soldiers be judged on their conduct in battle, not bed. JAMES SCOTTMilton Keynes,Buckinghamshire. Sir: Under normal circumstances the professional users of firearms, servicemen, are never allowed to take their personal weapons home. There is plenty of work to be getting on with down here (which could do with some of that nice Martian money) even if it is not so glamorous or photogenic as a trip to Mars.JUSTINE KELLERGlasgow.

Sir: So "the army's position on gender is perfectly PC, moving happily with the times?" (Magazine 10 August). To uncover an independent fossil record - or better, genetic code - would have fantastic impact upon many fields of research. But it is here that I must praise Mr Arthur for bringing us humbly back to Earth: we simply do not have the technological ability to usefully (let alone economically) mine for Martian fossils. One of the great frustrations to those many scientific disciplines concerned with the origin and evolution of life on Earth is want of a comparison: we have, as yet, only one example of a life strategy and so it becomes terribly difficult to isolate those features of it which are indispensable and those which are not (could, for instance, some other system replace our genetic code?). I am an astronomer, and while my kind may enjoy greater public appeal than most other scientists (no mice, no BSE, lots of big colour pictures) we do get embarrassingly expensive at times. Whenever some $1bn extravagance winds up in the swamp, I find myself furtively avoiding those colleagues across the road in life sciences who are struggling for rat feed and wretched for a week if they crack a Pyrex flask. However, Mr Arthur is unjust to paint us all as rabid alien-hunting trekkies: if there really are fossils on Mars, this discovery is as important to those unravelling life on Earth as it is to those who seek (or fear) it elsewhere.