Final answer:
HAART involves a combination of different drugs to combat the high mutation rate of the HIV virus and prevent resistance.
Step-by-step explanation:
The evolutionary rationale behind Highly Active Anti-Retroviral Therapy (HAART) is to combat the high mutation rate of the HIV virus. When individual drugs are used, the virus can easily develop resistance. HAART involves a combination of different drugs to attack the virus at different stages of its replicative cycle, making it more difficult for the virus to develop resistance to multiple drugs at the same time.