This is partly due to defects in a particular type of specialised cell found in the pancreas.

BBC: Diabetes hormone treatment hope

The other, which faces a specialised type of solar cell made of a material called indium gallium arsenide, is sculpted into a structure called a photonic crystal that causes it to emit infra-red radiation selectively at the frequency best absorbed by the cell.

ECONOMIST: Solar power

The adult cells are thought to revert to a state similar to that of embryonic stem cells, which are even less specialised, before becoming the new cell types.

BBC: Stem cell research doubts