The answer to that question you are asking is "guardian"
Answer:
lack knowledge of geographic al feature lack of manpower necessary to operate the work
I believe the answer is: holding genetics constant while varying the environment.
This could be done by making the identical twins grow up in a different environment. If the behaviour that they displayed is exactly the same even if they grow up in a different environment, the only explanation for that is their behaviour is influenced by genetics, and vice versa.