Question: I have heard that some amphibians are able to re-grow limbs, and some scientists believe that they would be able (to some extent) make this possible in humans, for soldiers and people who have lost limbs. A) Is this theory correct? B) If it is, then do you think this would be a good idea, or could we be facing mutations, and see a result like that of \"I am legend\" ?

Stephen Curry answered on 17 Jun 2010:

Hi caragh26 – very interesting question. It is certainly true that some amphibians (e.g. frogs) can regenerate limbs they have lost. I don’ think we fully understand yet why they have this capacity and yet mammals do not.

I do think there could be a good chance of exploiting this capability in medicine once it has been figured out.

To ‘program’ humans to have this capability from birth would require genetic engineering of embryos and I’m not sure about the ethics of that one. I am comfortable with trying to eliminate killer diseases that way but making other wholesale changes could have unpredictable effects.

But it’s a tricky area because disease-causing mutations can sometimes have benefits. For example, some mutations in the gene for haemoglobin lead to sickle-cell anemia. The mutation causes an alteration in the hemoglobin protein that makes it form long fibres; these fibres distort red blood cells, which end up blocking the fine blood vessels in the body. If both your haemoglobin genes (from Mum & Dad) have the mutation, you are unlikely to live beyond your 30s. However, people with one mutant copy and one normal copy of the haemoglobin gene are *more* resistant to infection by malaria.

So in that case, it would be hard to know what engineering choice to make.