The researchers believe modern speech and language first emerged in Homo heidelbergensis, an extinct species of the genus Homo that lived in Africa, Europe and western Asia from at least 600,000 years ago and possibly much earlier than that. This species might have been the common ancestor of Homo sapiens and Neanderthals.
Dediu and Levinson's work counters the theory that a single, or very few, genetic change(s) resulted in the acquisition of the capacity for language. Instead, the scientists hold that genes associated with language and culture co-evolved.
"The basic idea," Dediu explained, "is that cultural change is not simply an effect of a better genetic background; culture does not have to wait for biology change, but culture generates new selective pressures to which our biology must adapt, changes in biology that might allow new cultural changes in a co-evolutionary cycle."
The evolution of lactose tolerance and changes to our immune and digestive systems due to farming are all examples.
As for when an individual of any species first communicated in a complex way via sound, it's possible the sound was a whistle, Mark Sicoli, an assistant professor in Georgetown University's Department of Linguistics, told Discovery News. Sicoli studies whistled speech still used in parts of Oaxaca, Mexico.
"Hypothetically, whistled speech could be as old as the earliest languages," Sicoli said, adding that it could even have been a component of proto-language, the precursor of human language used by the earlier hominid species.
Since Neanderthals and some humans out of Africa interbred and otherwise spent time together, we could retain aspects of Neanderthal communication that persist to this very day.
"If our proposal is correct," Dediu concluded, "then we might not only carry some Neanderthal genes in our own genomes as traces of our past encounters, but also our languages might as well preserve some faint signature of their languages as well, but until rigorous testing is attempted, this must remain pure -- even if exciting -- speculation."