Final answer:
The case history of mnemonist Rajan Mahadevan suggests that exceptional memory is primarily a genetic trait independent of practice or learning. Research has shown that hyperthymesia, which is a rare exceptional memory ability, is believed to be linked to specific genetic factors.
Step-by-step explanation:
The case history of mnemonist Rajan Mahadevan suggests that exceptional memory is primarily a genetic trait independent of practice or learning. This is supported by the fact that Rajan displayed exceptional memory abilities from a very young age, without any intense practice or training.
Research has shown that exceptional memory abilities, such as hyperthymesia, are rare and are believed to be linked to specific genetic factors. It is important to note that while innate ability plays a significant role, practice and learning can also enhance and refine memory skills.