Prediction and Application
Unlike sciences such as physics and evolutionary biology, immunology has not to date been much motivated by predictive synthetic theories.
Now that it is clearly possible to empirically partition defenses into tolerance and resistance, it should be possible to develop and test hypotheses about their relative importance in different circumstances.
A natural hypothesis is that the fitness benefits and costs of resistance and tolerance vary across environmental conditions, favouring different combinations of these two components of defense under different circumstances [15].
For example, it has been argued that a high rate of infection but low virulence should select for host tolerance, whereas the opposite should favour resistance [16].
Similar adaptive scenarios can be envisaged for variation in, for example, host reproductive status and age and body condition.
Testing such adaptive hypotheses would move the study of animal defenses beyond elucidation of mechanism.