Mitochondria are the cell’s batteries, little structures inside every cell that provide our energy. They have a most curious property in that they have their own DNA, separate from the rest of our DNA, that is only inherited from the mother. The other oddity about the mitochondrion is its genesis. It is now virtually certain that mitochondria were once free living single celled creatures. Life in those days – we’re talking of around 2 billion years ago – consisted only of single-celled creatures: life was a matter of one cell engulfing another and digesting it: the war of the cells. It wasn’t a pretty world, by our standards, and this went on for about 1 billion years before multicellular organism began to evolve. But sometimes, instead of one cell consuming another, both cells found an accommodation: one continued to live inside another and both benefited: symbiosis. This also happened in the line that led to plants: the green of plants comes from the photosynthetic chloroplasts, also once free-living organisms.
Over time, many of the genes in the mitochondria have been lost or been incorporated into the host genome – only 37 remain. But the mitochondria are vital – if they seriously malfunction, life is not possible.
So when genetic modification of mitochondria is proposed what we are really talking about is not human genetic modification but a form of bacterial modification: the bacterium just happens to be part of us. We don’t scruple to tinker with our most basic bits of plumbing. If the heart is failing we implant a pacemeaker. This is not considered to be dehumanizing. But tinkering with our genes is thought by some to transgress human integrity. This is illogical. The team in question is at Newcastle University and the head, Professor Doug Turnbull, put it succinctly: "What we've done is like changing the battery on a laptop: the energy supply now works properly, but none of the information on the hard drive has been changed”.