Broad Spectrum Revolution

Why Ancient Humans Stopped Following the Paleo Diet

Libya, Sahara, Tadrart Acacus, cave art on sandstone wall
Cave Painting of Hunters at Tadrart Acacus, Algeria. Philippe Bourseiller / Getty Images

The Broad Spectrum Revolution (abbreviated BSR and sometimes referred to as niche broadening) refers to a human subsistence shift at the end of the last Ice Age (ca 20,000–8,000 years ago). During the Upper Paleolithic (UP), people all over the globe survived on diets made up primarily of the meat from large-bodied terrestrial mammals—the first "paleo diet". But at some point after the Last Glacial Maximum, their descendants broadened their subsistence strategies to include hunting small animals and foraging for plants, becoming hunter-gatherers. Eventually, humans began domesticating those plants and animals, in the process radically changing our way of life. Archaeologists have been trying to figure out the mechanisms that made those changes happen since the early decades of the 20th century.

Braidwood to Binford to Flannery

The term Broad Spectrum Revolution was coined in 1969 by archaeologist Kent Flannery, who created the idea to get a better understanding of how humans changed from Upper Paleolithic hunters to Neolithic farmers in the Near East. Of course, the idea didn't come out of thin air: BSR was developed as a response to Lewis Binford's theory about why that change happened, and Binford's theory was a response to Robert Braidwood.

In the early 1960s, Braidwood suggested that agriculture was the product of experimentation with wild resources in optimal environments (the "hilly flanks" theory): but he didn't include a mechanism that explained why people would do that. In 1968, Binford argued that such changes could only be forced by something that disrupted the existing equilibrium between resources and technology—big mammal hunting technologies worked in the UP for tens of thousands of years. Binford suggested that disruptive element was climate change—the rise in sea level at the end of the Pleistocene reduced the overall land available to populations and forced them to find new strategies.

Braidwood himself was responding to V.G. Childe's Oasis Theory: and the changes weren't linear. Many of scholars were working this problem, in all of the ways typical of the messy, exhilarating process of theoretical change in archaeology.

Flannery's Marginal Areas and Population Growth

In 1969, Flannery was working in the Near East in the Zagros mountains far from the impacts of sea level rises, and that mechanism wasn't going to work well for that region. Instead, he proposed that hunters began to use invertebrates, fish, waterfowl, and plant resources as a response to localized population density.

Flannery argued that, given a choice, people live in optimal habitats, the best places for whatever their subsistence strategy happens to be; but by the end of the Pleistocene, those locations had become too crowded for hunting big mammals to work. Daughter groups budded off and moved into areas that were not so optimal, so-called "marginal areas." The old subsistence methods wouldn't work in these marginal areas, and instead, people began exploiting an increasing array of small game species and plants.

Putting the People Back In

The real problem with BSR, though, is what created Flannery's notion in the first place—that environments and conditions are different across time and space. The world of 15,000 years ago, not unlike today, was made up of a wide variety of environments, with different amounts of patchy resources and different levels of plant and animal scarcity and abundance. Societies were structured with different gender and societal organizations and used different levels of mobility and intensification. Diversifying resource bases–and particularizing again to exploit a select number of resources–are strategies used by societies in all of these places.

With the application of new theoretical models such as the niche construction theory (NCT), archaeologists today define the specific shortcomings within a specific environment (niche) and identify the adaptations that humans used to survive there, whether they are expanding the dietary breadth of their resource base or contracting it. Using a comprehensive study known as human behavioral ecology, researchers recognize that human subsistence is a nearly continuous process of coping with changes in resource base, whether people are adapting to environmental changes in the region where they live, or moving away from that region and adapting to new situations in new locations. Environmental manipulation of the environment occurred and occurs in zones with optimal resources and those with less optimal ones, and the use of BSR/NCT theories allows the archaeologist to measure those characteristics and gain an understanding of what decisions were made and whether they were successful—or not.