What does a control group show in an experimental investigation? the effects that the scientists are causing by manipulating variables how nature would act without manipulation by the researchers why each part of a system is related to every other part all parts of a system that scientists are controlling and changingwhat does a control group show in an experimental investigation? the effects that the scientists are causing by manipulating variables how nature would act without manipulation by the researchers why each part of a system is related to every other part all parts of a system that scientists are controlling and changing