The first point to remember is that attempts to clone mice have actually been very unsuccessful for at least a decade. Sheep have been successful. So one asks, 'Where do humans lie?' Most people think they are somewhere between the two, but at least there's a reasonable chance they might be clone-able.

The earliest example known to me of replaced body parts is exemplified by a Mayan skull dating back to 1400 BC. In this skull, false teeth made of stone had been implanted.

The importance of the egg's non-nuclear material - the cytoplasm - in early development is apparent in the consistent relation that is seen to exist between certain regions in the cytoplasm of a fertilized egg and certain kinds or directions of cell differentiation.

For my part, I have worked all my life with eggs and embryos of frogs. Compared to other small animals, these have figured prominently in the world of literature.

I myself have been a major beneficiary of the view that no animal will more repay treatment that is kind and fair.

If you took some famous religious leader, for example, and said it would be nice to clone them indefinitely so you have a dynasty of leaders, my own guess would be that each time the cloning takes place, they would become more and more defective, presumably mentally defective and subsequently worse.

I have this rather amazing report which, roughly speaking, says I was the worst student the biology master had ever taught.

I remember that, at an early age, I spent many months making a three-masted sailing boat with rigging in a half-walnut shell.

In principle. what is done is to take the nucleus out of a cell with a very fine micro-pipette or needle and introduce it into an egg. That had been done with amphibians a long time ago, and then there was a long pause of many years before people were clever enough to make that work in the sheep.

If you explain to a patient what can be done and what might be the downsides, let the patient choose; don't have ethicists, priests, or doctors say you may or may not have replacement cells.