My critique of Engels essay, which consider very good in many other aspects, might be summarized by saying I think the title should be " The Transition in Labor in the Transition from Ape to Man ".
Notice Marx says: " An immeasurable interval of time separates the state of things in which a man brings his labour-power to market for sale as a commodity, from that state in which human labour was still in its first instinctive stage. We pre-suppose labour in a form that stamps it as exclusively human. A spider conducts operations that resemble those of a weaver, and a bee puts to shame many an architect in the construction of her cells. But what distinguishes the worst architect from the best of bees is this, that the architect raises his structure in imagination before he erects it in reality. At the end of every labour-process, we get a result that already existed in the imagination of the labourer at its commencement. He not only effects a change of form in the material on which he works, but he also realises a purpose of his own that gives the law to his modus operandi, and to which he must subordinate his will "////
Marx claims that human labor's distinct characteristic is that it is based on imagination, a plan or none other than thinking , a pre-thought, which means use of language. Whereas Engels famously takes great pains to describe the original human labor as distinguished from its ape predecessor as sort of inhering in the human HAND as an unthinking instinct when it was freed from use in locomotion by the development of upright posture and bi-pedalism; BUT independent of conscious thought and language:
"First, owing to their way of living which meant that the hands had different functions than the feet when climbing, these apes began to lose the habit of using their hands to walk and adopted a more and more erect posture. This was the decisive step in the transition from ape to man....The number and general arrangement of the bones and muscles are the same in both hands, but the hand of the lowest savage can perform hundreds of operations that no simian hand can imitate – no simian hand has ever fashioned even the crudest stone knife....But the decisive step had been taken, the hand had become free and could henceforth attain ever greater dexterity; the greater flexibility thus acquired was inherited and increased from generation to generation....On the other hand ( no pun intended , I guess, giggles) , the development of labour necessarily helped to bring the members of society closer together by increasing cases of mutual support and joint activity, and by making clear the advantage of this joint activity to each individual. In short, men in the making arrived at the point where they had something to say to each other. Necessity created the organ; the undeveloped larynx of the ape was slowly but surely transformed by modulation to produce constantly more developed modulation, and the organs of the mouth gradually learned to pronounce one articulate sound after another.
Comparison with animals proves that this explanation of the origin of language from and in the process of labour is the only correct one. ...First labour, after it and then with it speech – these were the two most essential stimuli under the influence of which the brain of the ape gradually changed into that of man, which, for all its similarity is far larger and more perfect."
Here's where I think Engels is specifically mistaken; when he says:" the greater flexibility thus acquired was inherited and increased from generation to generation...". He seems to think that the flexibility and skill of labor with "the" hand is inherited and increased from generation to generation by unthinking , non-linguistic "instinct", I guess. But this is fundamentally wrong. The way that humans pass on any skills learned in use of the hand in labor from one generation to the next is only by the use of language, culture, tradition, custom, myths , legends, etc. Not by some kind of developing instinct of "the" hand that would be an inheritance of acquired characteristics, a LaMarckian biological inheritance mechanism. The skill that an individual hominid , (upright/bipedal, hands free) learns in using its hands does not get transmitted to its offspring or future generations through its genes but through its culture and language. It is in what Marx termed its imagination, its thinking , contra Engels. So, not "first labour, after it and then with it speech", but " speech and the uniquely human form of thought, symboling and culture, from the very beginning along with "labour". Imagination, language , thought are part of the defining characteristic of human labor or productive activity as Marx says. Toolmaking , a very critical form of uniquely human labour or productive activity, can only be developed and perfected over many generations if the discoveries made by one generation are passed on to the subsequent ones; that new generations do not have to start from scratch. I say the unique human ability is not inventing the wheel, but not having to _re_invent the wheel each generation. Humans uniquely among animal species stand on the shoulders of giants , that is previous generations of the species in laboring or engaging in productive activity.
Another lesser point is that Engels has an overly narrow focus of labour as equated with use of hands. But the arms are also freed by the shift to upright posture/bi-pedalism. Most activity with hands requires use of the arms. An important specific form of the original human labour was certainly _throwing_ rocks or other missiles at predators or prey which action is probably more of the arms than hands. The same goes for whacking a predator or prey with a club. Even gathering fruit ,nuts and berries or fetching water involves the arms as much as the hands. So we must always say "hands _and_arms". Furthermore, use of the legs and feet are a necessary part of much of human labor. Can't go "over there" and gather fruit with the hands and arms without walking over there with your legs. Much labour may have been done by kicking or shoving things with the feet and legs or pushing from the legs. The upright posture would enable novel forms of kicking or shoving with legs and feet as compared with ancestoral hominoid species abilities. Marx actually says in the passage from _Capital_ above: He ("man"; sic) opposes himself to Nature as one of her own forces, setting in motion arms and legs, head and hands,"
The expansion of reference to arms, feet and legs is a minor point compared with the point that thought , language, culture, tradition, custom were integrated with expanded use of freed hands _from the very beginning _ , at the origin of human labour. There was a transition in labour,or life sustaining productive activity, in the transition from ape to man and the critical part of it was that it became guided by imagination, thought, culture, custom, tradition and language. That was the way that skills were accumulated in passing it on from one generation to the next. It was not an accumulation of unconscious or unthinking instinct, but conscious thought and "imagination".