Polymorphic/Metamorphic malware is written on low-level or high-level languages?

As a part of a course I study polymorphic/metamorphic malware. Every single paper and article I've stumbled upon mentions the techniques used by a malware to achieve polymorphism/metamorphism but non is mentioning the language(s) in which most polymorphic/metamorphic is written on or code examples of that particular technique.

My understanding is that malware can be written using almost any language, from Visual Basic, C and C++ to Java and Python. My question is: In order to achieve polymorphic/metamorphic behavior do you need a low level or a high lever language? Do we know which language most polymorphic/metamorphic malwares use?