Early Homo

The term proto-language, as defined by linguist Derek Bickerton, is a primitive form of communication lacking:

a fully-developed syntax;

tense, aspect, auxiliary verbs;

a closed-class (i.e. non-lexical) vocabulary.

That is, a stage in the evolution of language somewhere between great ape language and fully developed modern human language. Bickerton (2009) places the first emergence of such a proto-language with the earliest appearance of Homo, and associates its appearance with the pressure of behavioral adaptation to the niche construction of scavenging faced by Homo habilis.

Anatomical features such as the L-shaped vocal tract have been continuously evolving, as opposed to appearing suddenly. Hence it is most likely that Homo habilis and Homo erectus during the Lower Pleistocene had some form of communication intermediate between that of modern humans and that of other primates.

Steven Mithen proposed the term Hmmmmm for the pre-linguistic system of communication used by archaic Homo, beginning with Homo ergaster and reaching the highest sophistification in the Middle Pleistocene with Homo heidelbergensis and Homo neanderthalensis. Hmmmmm is an acronym for holistic (non-compositional), manipulative (utterances of commands or suggestions), multi-modal (acoustic as well as gestural and mimetic), musical, and memetic.

The discovery in 2007 of a Neanderthal hyoid bone suggests that Neanderthals may have been anatomically capable of producing sounds similar to modern humans. The hypoglossal nerve, which passes through the canal, controls the movements of the tongue and its size is said to reflect speech abilities.

Klein argues that the Neanderthal brain may have not reached the level of complexity required for modern speech, even if the physical apparatus for speech production was well-developed. The issue of the Neanderthal's level of cultural and technological sophistication remains a controversial one.

The development of fully modern behavior in H. sapiens, not shared by any other variety of Homo, is dated to some 70,000 to 50,000 years ago. The development of more sophisticated tools, for the first time constructed out of more than one material (e.g. bone or antler) and sortable into different categories of function (such as projectile points, engraving tools, knife blades, and drilling and piercing tools) are often taken as proof for the presence of fully developed language, assumed to be necessary for the teaching of the processes of manufacture to offspring.

The greatest step in language evolution would have been the progression from primitive, pidgin-like communication to a creole-like language with all the grammar and syntax of modern languages. Many scholars believe that this step could only have been accomplished with some biological change to the brain, such as a mutation. It has been suggested that a gene such as FOXP2 may have undergone a mutation allowing humans to communicate. Evidence suggests that this change took place somewhere in East Africa around 100,000 to 50,000 years ago, which rapidly brought about significant changes that are apparent in the fossil record. There is still some debate as to whether language developed gradually over thousands of years or whether it appeared suddenly.

The Broca's and Wernicke's areas of the primate brain also appear in the human brain, the first area being involved in many cognitive and perceptual tasks, the latter lending to language skills. The same circuits discussed in the primates' brain stem and limbic system control non-verbal sounds in humans (laughing, crying, etc.), which suggests that the human language center is a modification of neural circuits common to all primates. This modification and its skill for linguistic communication seem to be unique to humans, which implies that the language organ derived after the human lineage split from the primate (chimps and bonobos) lineage. Plainly stated, spoken language is a modification of the larynx that is unique to humans.

According to the Out of Africa hypothesis, around 50,000 years ago a group of humans left Africa and proceeded to inhabit the rest of the world, including Australia and the Americas, which had never been populated by archaic hominids. Some scientists believe that Homo sapiens did not leave Africa before that, because they had not yet attained modern cognition and language, and consequently lacked the skills or the numbers required to migrate. However, given the fact that Homo erectus managed to leave the continent much earlier (without extensive use of language, sophisticated tools, nor anatomical modernity), the reasons why anatomically modern humans remained in Africa for such a long period remain unclear.