A representative subset of the target population can be chosen. This sample is then used to predict functional relationships in the population by virtue of its deliberate similarity. Alternatively, the population values can be predicted based on data obtained from a synthetic model. The prediction in this case is based on the functional similarity between the model and target. Synthetic subjects are often chosen to allow the maximum degree of control over confounds and to be maximally revealing of the phenomenon of interest.
Generality is based on understanding what is going on.
Additional important considerations include the convenience of using a particular synthetic subject. A rat is simply easier to deal with than a whale or a person. The optimal synthetic subject is also one which is optimized to reveal information on the dimension of interest, e.g., giant axons of squid. This is especially true in pure research settings where the goal is understanding general mechanisms of action rather than developing an analog of a specific applied problem. Alternatively, representative samples can be used.