Towards an understanding of the costs of fire

The ability to produce fire at will and to maintain it for a long duration is considered one of the major advances in human evolution. The exact process by which hominins first learned to use and to create fire is still hotly debated, with some arguing for a sudden transformative event that was quickly followed by a biological and cultural dependence on fire, such as a reliance on the extra calories saved through cooking food and an external source of heat. Others suggest that the 'domestication' of fire was a long and drawn-out process, with hominins using fire when it was available on the landscape but perhaps not having the ability to produce fire until much later in human history. In this paper we propose a third option, that fire should be considered like other technologies - that is, it certainly comes with benefits but also with costs, and that hominins functioned as optimal foragers who chose to use this tool only when the costs were less than the benefits. The potential benefits of fire have been well-described in other publications. Here we discuss in detail the various kinds of costs associated with fire and how these costs could, and do, structure human fire-use behavior. We then describe a small experiment to 'put some numbers on' the potential costs of fire, by quantifying one of the most expensive costs (fuel collection) and comparing it to one of the most-praised benefits (cooking of food). The results suggest that the costs of fuel collection are very high in less-forested environments, and that excessively large amounts of cooked foods are needed to match the total costs of fuel collection and the act of cooking. Overall, the costs of fire can be quite high and must be considered when proposing models for pre-modern human adoption and regular use of fire technologies.