Life,
as we have been studying it, starts off with small single celled organisms and
gradually includes more and more multicellular ones. The introduction of these
larger organisms has not by any means replaced the single celled one on this planet.
This impels one to consider whether there is any difference in the actual cells
found in either group that could account for this. If all things are made up of
the same building blocks, and we are all composed of cells, does that mean that
they are all the same cells?