All other groups of animals are thought to produce genetically innate vocalizations.
To understand this concept, it is important to distinguish vocal learning from auditory learning. Auditory learning is the ability to make sound associations, such as a dog learning how to respond to the sound "sit". All vertebrates have auditory learning.
Vocal learning is the ability to imitate sounds that you hear, such as a human or a parrot imitating the sound "sit". Currently only vocal learners have been found to have forebrain regions dedicated to vocal learning and production of these learned vocalizations. Vocal non-learners only have been found to have non-forebrain vocal regions responsible for the production of innate vocalizations." http://www.jarvislab.net/Evolution.html
That's kind of what I meant: surely that speech gene is not a gene that describes a whole brain?
"The question is why this gene is present in aquatic mammals and is absent in terrestrial apes"
Doesn't that refute the "speech gene" theory? Surely some terrestrial apes also communicate by "speech"?
I don't know enough about genetics to confidently discuss this more. Presumably if several species share a gene, they are likely to have a common ancestor?