“THERE is not much point in being multicellular if all your cells are the same. It is division of labour and specialisation of cell function which gives animals and plants their edge in the struggle for life.

How that specialisation comes about, though, is understood only hazily. Most cells in any given body have the same set of genes. The trick is that only about half of those genes are switched on. Some (those involved in basic metabolism, for example) are active in pretty well all cells. But a majority work in only a few sorts of cells, or possibly even just a single cell type. ” View more …