John Sulston developed techniques to study all cell
divisions in C. elegans, from the fertilized egg to the
959 somatic cells in the adult nematode. In 1976, Sulston
described the cell lineage for a part of the developing
nervous system. He showed that the cell lineage is invariant,
i.e. every nematode undergoes exactly the same
programme of cell division and differentiation.

As a result of these findings, Sulston discovered that specific
cells in the cell lineage always die by programmed
cell death. This could be followed in the living organism.
He described the visible steps in the cellular death process
and demonstrated the first mutation of a gene participating
in programmed cell death, the nuc-1 gene.