Paleoanthropologists acknowledge that our early hominin ancestors would have used tools manufactured from perishable materials prior to the appearance of the earliest stone artifacts, but we have largely eschewed hypothesizing that the plant-based culture of this period was a measurable driving factor in human biological and behavioral evolution. In The Botanic Age, Dean Falk argues that during the period from 6.5 through 3.5 million years ago, the elaboration of a plant-based behavioral suite was foundational to the development of major features that separate us from other apes: bipedalism, cognitive complexity, and language. Although the direct physical evidence, outside of hominin fossils, is understandably nonexistent, Falk weaves The Botanic Age together with support from a wide range of fields, including primatology, ethnography, experimental archaeology, and evolutionary developmental biology. Some of the ideas expand on Falk’s own work, but in many places they rely on the expertise of others. This point is noteworthy because The Botanic Age includes an interview section with eight individuals whose work particularly inspired Falk’s thinking on the topic—a refreshing practice that I hope other authors will consider.

Using the universal ape practice of building sleeping nests in trees as a point of departure, The Botanic Age proposes that our hominin ancestors applied their knowledge of working with plant raw materials to new domains when they moved to the ground in response to forest fragmentation caused by late-Miocene climate change. Falk argues that bipedalism developed in this context as an adaptation advantageous for the acquisition of necessary materials, which were now further separated in space, to fulfill the evolutionary-programmed requirement to build sleeping nests. This compelling hypothesis ties the origins of bipedality directly to reasonably assumed existing practices as opposed to invoking a need to carry novel objects or resources. In this sparser canopy environment, some individuals started to nest on the ground, promoting prosocial cooperative networks for protection from predators and leading to changes in sleep patterns with substantial implications for cognition. Human sleep, Falk explains, is much shorter than that of chimpanzees, likely as a response to the need and demands of surviving on the ground at night in the company of nocturnal predators. A happy evolutionary accident of this development is the maintenance and consolidation of REM sleep—crucial for emotional regulation and creative inspiration—into longer chunks of time.

After The Botanic Age describes how the seeds of bipedalism and higher cognitive abilities were planted in the pre–Stone Age period, Falk sets out to illustrate how these factors were also preconditions for human-like language capabilities. Increased bipedal activity resulted in morphological changes, particularly the lack of opposability in the big toe. A direct result of this development would have been the loss of ape-like gripping abilities for hominin infants. Here is where Falk’s model really comes into focus: it explains how hominins—likely hominin mothers—applied the long-standing knowledge of weaving plant materials for nests to the invention of baby slings. Once baby slings were invented, it would have been a short step to recognizing that they could similarly be used to carry resources or raw materials back to a camp site, potentially setting up a sexual division of labor. As hominins became accustomed to carrying heavy loads—again, most probably female hominins—they would have needed to place their babies down, resulting in vocal protestations. Falk, building on their previous work, reasons that infant-directed language must have quickly developed in these contexts to help reassure and soothe infants as a replacement for physical contact. Ultimately, such vocalizations would have developed into lullabies and, eventually, more formal language.

On the surface, The Botanic Age does not provide any new hard evidence or even a completely novel set of hypotheses, but Falk should be praised for directly addressing the contributions of the period of our human history prior to the appearance of preserved material culture. Although some researchers have speculated that complex cognitive abilities and language capacities developed with Homo erectus starting after two million years ago, The Botanic Age suggests that these features owe their origins to the environmental circumstances and social relationships of an earlier stage of our evolutionary history. In fact, Falk argues that the development of stone-tool technologies may not have been as much of a cognitive leap as has often been hypothesized, but instead a strategy for making more efficient tools out of wood and other perishable materials. In proposing woodworking as a primary impetus for the invention of stone tools, Falk points to use-wear analyses indicating that early stone tools were used for processing botanical material and that some primates used sharpened spears for capturing insects, grub, and other small prey. As with connecting the origins of bipedality to preexisting ape practices of nest building, Falk offers a similarly logical explanation that sharp stone edges would be superior to manual labor for refining existing botanical tool kits without having to invoke new practices of scavenging or hunting. Paleoanthropologists and researchers in allied fields will find a number of fertile hypotheses in this long-overdue model for the significance of the botanic age to our origins.