Let's think big. How can one encompass the entirety of human history, and prehistory, in a single volume? A variety of answers are possible. They have a history too, which one of this brace of contemporary efforts also tries to encompass. The other offers an attempt at a new synthesis, which is impressively broad in its incorporation of insights from a range of historical sciences.

The framework that Patrick Manning's A History of Humanity sets up this way is reasonably promising. The way to build an intelligible overview, he argues, is to focus on systems, and how they have enlarged and grown more complex. That has happened, he relates, mainly through the growth of institutions – a term which, like ‘systems’ itself, he uses with maximum generality. They are ‘structures formed and maintained by members to achieve agreed-upon purposes’ (p. 43), and are the basis of social evolution. They include speech, agriculture, ceramics, migration, libraries, the state, war, and – yes – science.

A definition broad enough to cover all those may lack analytic power. Still, it allows some further bold generalization. Human history can be read as a story of innovations producing new institutions, ‘and the internal logic of each institution brought into play the dynamics necessary to sustain the character of activity in that new institution’. Some readings of that are tautologous, but Manning goes on to give enough specifics to allay that anxiety, most of the time.

The trigger for the key transition to systems with a new character was the first institution listed, speech. Manning's story, speculative but he suggests that it fits known facts, is that human systems consisted of extended family groups until around 70,000 years ago. Then, unprompted, as it were, one group in North East Africa invented spoken, syntactic language, which spread to others and made all the other institutions possible. All this is framed by an account of the braided paths of biological, cultural and social evolution, along with evolution of Earth systems (summarized as Gaia) though the account of the relations between them isn't always clear. Manning endorses the idea that all three evolve by some quasi-Darwinian mechanism, but the mechanics of this for cultural and social evolution are too vague to carry conviction.

Nevertheless, there is much to ponder here, as well as plenty to critique. Any book with such a grand ambition is bound to fall short – but it is more interesting to look for aspects that are reasonably successful. Manning is noteworthy for sketching a world history that brings together genetic (and epigenetic) data with language distribution, archaeology and demographic history to trace the sequence of migrations and the continual extension of human networks that underpin more and more complex exchanges, and more ramified institutions.

Rees and Sleigh's slimmer volume examines our position from several different points of view. A capstone in Reaktion's now vast but always worthwhile series in which each volume describes a different species and its cultural history, it has to take a different tack from all the others. Humans are the species that writes books, the one that lives cultural history or, indeed, history.

The co-authors’ brief here is thus both more and less demanding than Manning's. More because it has to take some account of cultural history in its entirety (another obviously impossible task). Less because, while rooted in academia, the series presents free-wheeling personal reflections, designed to inform and stimulate in less than two hundred pages. Authorial chutzpah, rather than scholarly detail, is at a premium. The job is to offer as many things as possible, loosely connected, to divert, entertain, and provoke further investigation, without doing anything intellectually disreputable.

And they succeed well. Six illustrated chapters each cover a topic that may, or may not, help define the essential attributes of humanity. In each case, that depends crucially on similarity or contrast, and on the negotiated boundaries between categories. Humans may be similar to, but also usefully distinguished from, beasts, other hominins, machines, gods or aliens. Exactly how is a matter for continual cultural work, often in service of maintaining or attacking power structures. This comes through especially clearly, unsurprisingly, in the chapter headed ‘She’, which elucidates how women's human status has typically been judged (by men) according to how they behave. Any claim to female equality, usually received as a bid for dominance, is deemed to risk sacrifice of what males define as humanity.

The two books come together in accepting the contemporary obligation to situate overviews of human culture, society and evolution as part of a story that leads to the Anthropocene, and to offer suggestions about its significance. For Rees and Sleigh, this leads to a concluding chapter reflecting on the history of a species that knows it is human, but does not know what a human is. They relate again how efforts to define humanity end badly, usually leading to inhumane treatment of those deemed to lack some putative essential human quality. They retain a sympathy for the idea that humans are uniquely cooperative. ‘The global success of our species is based on our ability to act in concert’ (p. 169), they write. Manning would agree.

They propose that the best way for we humans to locate ourselves today is not via humanism, or any of several varieties of posthumanism, but ‘imhumanism’. This is a play in immanence, denoting the idea that humanity cannot be abstracted or separated from actual humans. Instead, it is ‘assumed to exist as a quality that simply inheres in the human’ (p. 176). It cannot be possessed. But can be given away, or attributed to or conferred on others.

The examples that follow, such as conferring humanity on the dead, or on slaves, underline how it must be done in culturally sanctioned, and often contested, ways. So perhaps the next step is to say that humans are the creatures that argue about what it is to be human, and who merits the designation.

Rees and Sleigh take a different path, discussing the extension of legal standing, and personhood of a kind, to entities (trees, rivers, machines) that others do not consider human. They go on to say that imhumanism points to a celebration of shared humanity, and that extending that beyond a single species might ‘save’ Homo sapiens in the Anthropocene. This seems enigmatic in its global import, but does solve a more immediate difficulty: ending a book on an impossibly expansive subject.

Manning's authorial solution to the same problem is to review institutions that have arisen or grown explosively in the last two centuries. As before, his inventory is broad, including popular culture and its institutions, and institutions of general and specialized knowledge – science again. Add these to newcomers like corporations, trades unions, nations and international organizations, he suggests. Then consider how they all interact. One result of that interaction is the advent – more as aspiration than as reality – of global democratic discourse. That, he suggests, offers hope for a collective means of taking decisions about ‘modification of the Human System itself and its ties to the natural world’ (p. 236).

He wisely leaves open the question whether this is feasible. The vision of humanity as a species somehow having a conversation with itself/ourselves about the future of the entire planet may raise doubts occasioned by the lived experience of modern global media, and social media. But he outlines hopes not for a world government, but for a developing global discourse that helps along ‘the discussion and distillation of knowledge-based ideologies … appropriate to workable social priorities for humanity’ (p. 255). That slightly curious formulation is hard to prise open. But I think one can hear a faint echo of the Enlightenment in this appeal for real knowledge, in some sense, helping social movements gain traction, enough to help them lift the human system (or Human System – you decide) out of its current self-made crises. Like him, I guess I am still hoping.