Using one relevant research study, show how a principle that defines the biological level of analysis may be demonstrated.

        Rosenzweig wanted to test if a common thought of many people was true, he wanted to see if having more experiences the brain of beings would get bigger. The researcher decided to get some rats as participants and for several weeks to position them in one of three conditions: a standard condition with average space, company, food, and water at any time; an enriched condition with rats with more than average space, company, food, water and every day new toys to play with; and an empovirished condition with rats isolated from the others and with the minimum necessary to live. Here the use of rats was very helpful since testing such an hypothesis on human beings would have been problematic. This is caused by the fact that not only such a test would be ethically immoral because it would put the participants under possibly dangerous deprivation situations, but it would also be problematic to calculate the increase in size of the brain of the participants. In this situation the use of animals such as rats was encouraged since the brain of rats is flat and less complex than the brain of bigger mammals. Rats are also very cheap to buy, which is something for which researchers often have to think about unfortunately. Finally the ethical considerations are less important than in a situation with humans tested.

        This experiment was conducted with the use of animal testing for several reasons, and this demonstrated that animal research can be very helpful also when there is the need to understand a human situation. Unfortunately there have been some critiques for the fact that there is no proof of the fact that these results could also be applied to human beings.