Looking at Steven Mithen’s Book (2024) “The Language Puzzle” (Part 7 of 23)
0053 Well, after making a commitment to vocalization as the only pathway for the evolution of language, chapter fivecovers speaking and hearing.
Here is snapshot.

0054 This comparison is only the start. Because vocalization is not under voluntary control at the start of bipedalism, the lineage will have to wait almost three million years before language can evolve with Homo heidelbergensis (who appears along with or after the domestication of fire, between 0.8 and 0.6 Myr).
Or something like that.
0055 So, why not start with manual-brachial gestures? Bipedalism (present by 3.5 Myr) enslaves the foot and frees the hand. The arms and hands are already under voluntary control. Plus, manual-brachial gestures can pantomime and point. They can serve as iconic and indexal natural signs. The referents are imaged or pointed to.
The next challenge is to frame displacement in terms of two issues. First (M), a chimpanzee will almost always use its general intelligence to solve problems to get food for itself. In other words, the great apes forage for themselves. Second (N), there must be a way to frame the displacement that occurs with manual-brachial gestures.
0056 Indeed, these issues crop up in chapter six, concerning iconic and arbitrary gestures… er… words.

0057 I start with the first issue (M). The period of concern starts at 4.5 My and accounts for the emergence of the earliest species of the Homo genus, around 2.5 Myr, along with Oldowan stone tools.

0058 Two adaptive changes (M1 and M2) key into the transition from living in tropical forests (characteristic of the common ancestor, at 7 Myr) to mixed forest and savannah (at 4.5 Myr).
0059 The first adaptive change (M1) is anatomical. Bipedalism enslaves the foot and frees the hand to carry things, ranging from babies to rocks. Also, the hands (“manual”) and arms (“brachia”) are capable of communicative gestures. Bipedal species travel from one location of seasonally rich resources to another. They travel in bands (50). So, a certain amount of cooperation among family (5) and friends (5) is necessary.
0060 The second adaptive change (M2) is… well… may I say, “cultural”?
With all the travel, settling in and packing out, there is less time for individual foraging. Indeed, individual foraging does not provide enough to keep each person in the band alive.
However, a team of around 15 souls can gather enough to feed a band of 50. Well, no one thinks of it so analytically. On a good day, a team of around 15 can gather enough to feed all their family (5) and friends (5). Yes, that covers everyone in the band, more or less. On any given day, a band of 50 supports two or three teams. One is bound to get lucky.