The essential properties which distinguish a human language from apes' communication systems can be identified. Some of them are presuppositions – called preadaptations in Hurford 1999 – for more advanced properties and can, to some extent, be arranged in temporal order. As for fixing dates at which certain milestones in the evolution of human language were reached, we are limited to educated guesses (Hurford 1999).

Homo erectus had acquired bipedalism. By walking on the legs, hands are free for gestures. In the following two million years, brain size doubles. Especially the posterior human brain, which is active in semiosis, is much larger in humans than in apes (Lieberman 2002: 52). In the same period, use and production of ever more sophisticated tools increases.

While all hominids show aggressive behavior inside their species and even their group, this is paired with enhanced social interaction in hominini. Probably on the basis of a more developed mirror-neuron system and consequently increased empathy among peers, Homo erectus elaborates the theory of mind of which apes possess a rudimentary form, and develops shared intentionality (Keller 1995, Tomasello 2008, Terrace 2019).

Already at the stage of primates, semiosis is available in the form of gestures and cries. As Wernicke's area develops, the brain becomes more efficient in interpreting sounds perceived as indexes and, thus, in inferring their repraesentatum (Keller 1995, ch. 10). In producing signs to be understood by peers, Homo erectus also uses icons, viz. onomatopoetic and sound-symbolic signs. Later, at the stage of Homo sapiens, this capacity also appears in art, as this uses icons and symbols.

Human motor control develops specific abilities beyond those of non-human primates. This even includes manual control. For instance, although chimpanzees can throw objects, Homo erectus improves this ability significantly (Calvin 1983). Motor control is also an evolutionary basis of cognitive abilities and semiosis, both the structuring of the sense of a message and its coding by sound:

• The neural mechanism that converts a possibly complex goal into a series of steps and issues the commands that coordinate movements for their execution adapts to converting an idea into a set of components and coding these by a series of signs (Lieberman 2002: 53).
• In non-human primates, the laryngeal motor cortex is part of the premotor cortex and only indirectly connected to the laryngeal motor neurons in the brain stem, which innervate the laryngeal muscles. In humans, the laryngeal motor cortex is located in the primary motor cortex and directly connected with the laryngeal motor neurons. This development contributes to the ability to speak and vocalize voluntarily (Simonyan & Horwitz 2011: 197).
  The vocal tract of Homo erectus develops into the shape seen in Homo sapiens. Enhanced neural equipment enables fine sequential and simultaneous differentiation, so that the apparatus of phonation and articulation can form and combine the speech sounds characteristic of language. Humans can transmit up to 30 phones per second. Apes' cries are far from this.

The auditory apparatus becomes capable of fine differentiation on the temporal (serial) and the simultaneous axis. These refinements of motor and sensory control may have started with Homo heidelbergensis (ca. -700,000).

Once displaced reference has become possible, prevarication is possible, too. Pre-human primates already know they can be cheated. Nevertheless, they develop language further to full effability, on the basis of shared intentionality and mutual trust.