This experiment helps to prove evolution and it’s mechanism natural selection because it shows the adaptation of a species over extensive periods of time in establishing traits that were ultimately beneficial to the survival of the caminacule or at lest not detrimental to it’s survival.
A catastrophic drop in population is the prime factor. This of necessity always precedes extinction. If a species has suffered such a decline you look first for environmental factors as a cause. If there has been no dramatic change in the environment ex disruption or flooding of habitat or changes of weather patterns, then look for pollution, then disease, then excess predation or competition, and lastly a similar decline in another species on which the species under study is dependent. If none of the above then it is just possible that such declines are part of a natural cycle. However this should never be assumed until the aforesaid possibilities have been eliminated.