In biology, apoptosis (from the Greek words apo = from and
ptosis = falling, commonly pronounced ap-a-tow'-sis) is one of
the main types of programmed cell death (PCD). As such, it is a
process of deliberate life relinquishment by an unwanted cell in
a multicellular organism. In contrast to necrosis, which is a
form of cell death that results from acute cellular injury,
apoptosis is carried out in an ordered process that generally
confers advantages during an organism's life cycle. For example,
the differentiation of human fingers in a developing embryo
requires the cells between the fingers to initiate apoptosis so
that the fingers can separate. The way the apoptotic process is
executed facilitates the safe disposal of cell corpses and
fragments. Since the beginning of the 1990s, research on
apoptosis has grown spectacularly. In addition to its importance
as a biological phenomenon, defective apoptotic processes have
been implicated in an extensive variety of diseases. Too much
apoptosis causes cell-loss dis