Apoptosis Occurs Because...

Why does apoptosis occur? Apoptosis is defined as programmed cell death, but why would cells program their own death? Also, does apoptosis occur only in higher level organisms or does it occur in organisms like bacteria and fungi as well? Luckily for us, this article answers all of these questions.
Let's attack this question by question. So, why does apoptosis occur? There are several reasons for programmed cell death. To name a few:
1. Some cells are generated in excess and only the ones that become properly functional survive. i.e. Nervous System
2. The mechanism that generates a certain type of cell luckily generates unneeded along with needed cells. Some cells that are needed die with time, but since there were extra unneeded cells produced, the individual is okay. i.e. Immune System
In essence, cells are programmed to die because they are harmful or because it takes less energy to kill them than to maintain them. Programmed cell death occurs to get rid of cells that are not needed, in the way, or potentially dangerous, as Michael Hengartner, the Senior Staff Investigator at Cold Spring Harbor Laboratory, put it.

Now on to another question. Does apoptosis occur amongst unicellular organisms? In a unicellular organism apoptosis could be akin to suicide! Nonetheless, studies have shown processes that scientists consider to be apoptosis in single-celled organisms. The death of the mother cell during sporulation (the process of creating spores) could be considered to be programmed cell death. Some parasites, like trypanosomes change form to escape the immune response from their host. The organisms that fail to change shape just kind of die off.