Final answer:
The most complex use of singing language among mammals is observed in great apes and cetaceans, with humans having the most developed form. The unique human vocal tract and specific genetic mutations like those in the FOXP2 gene support complex language development.
Step-by-step explanation:
The most complex use of a singing language among mammals might belong to species of great apes and cetaceans, specifically primates and whales. While the communication systems of nonhuman primates do not exhibit the same flexibility and infinite recombination found in human language, some species like chimps and bonobos reveal a capacity for complex vocalizations. Similarly, the elaborate songs of whales, known for their low frequency capable of traveling long distances underwater, suggest a sophisticated aural communication method among these marine mammals.
Humans, equipped with a unique vocal tract, including a descended larynx and a large, rounded tongue, have developed the most complex form of language known. This complexity includes the creation of tens of thousands of words from fifty distinctive phonemes. Furthermore, the slight mutation found in the human FOXP2 gene compared to that of other primates likely played a role in the emergence of spoken language in our ancestors.
These complex communication methods in great apes and cetaceans hint at the biological underpinnings that may have laid the foundation for the extraordinary linguistic capabilities seen in humans.