Where Do Humans Really Rank on the Food Chain?

It's a platitude that we've all heard dozens of times, whether to justify our treatment of other species or simply to celebrate a carnivorous lifestyle: humans are the top of the food chain.

Ecologists, though, have a statistical way of calculating a species' trophic level—its level, or rank, in a food chain. And interestingly enough, no one ever tried to rigorously apply this method to see exactly where humans fall.

Until, that is, a group of French researchers recently decided to use food supply data from the U.N Food and Agricultural Organization (FAO) to calculate human tropic level (HTL) for the first time. Their findings, published today in the Proceedings of the Natural Academy of Sciences, might be a bit deflating for anyone who's taken pride in occupying the top position.

On a scale of 1 to 5, with 1 being the score of a primary producer (a plant) and 5 being a pure apex predator (a animal that only eats meat and has few or no predators of its own, like a tiger, crocodile or boa constrictor), they found that based on diet, humans score a 2.21—roughly equal to an anchovy or pig. Their findings confirm common sense: We're omnivores, eating a mix of plants and animals, rather than top-level predators that only consume meat.

To be clear, this doesn't imply that we're middle-level in that we routinely get eaten by higher-level predators—in modern society, at least, that isn't a common concern—but that to be truly at the "top of the food chain," in scientific terms, you have to strictly consume the meat of animals that are predators themselves. Obviously, as frequent consumers of rice, salad, bread, broccoli and cranberry sauce, among other plant products, we don't fit that description.

The researchers, led by Sylvain Bonhommeau of the French Research Institute for Exploitation of the Sea, used FAO data to construct models of peoples' diets in different countries over time, and used this to calculate HTL in 176 countries from 1961 to 2009. Calculating HTL is fairly straightforward: If a person diet is made up of half plant products and half meat, his or her trophic level will be 2.5. More meat, and the score increases; more plants, and it decreases.

With the FAO data, they found that while the worldwide HTL is 2.21, this varies widely: The country with the lowest score (Burundi) was 2.04, representing a diet that was 96.7 percent plant-based, while the country with the highest (Iceland) was 2.54, reflecting a diet that contained slightly more meats than plants.

On the whole, since 1961, our species' overall HTL has increased just slightly—from 2.15 to 2.21—but this averaged number obscures several important regional trends.

A group of 30 developing nations in Southeast Asia and Sub-Saharan Africa (shown in red)—including Indonesia, Bangladesh and Nigeria, for example—have had HTLs below 2.1 during the entire period. But a second group of developing countries that includes India and China (shown in blue) has slightly higher HTL measures that have consistently risen over time, going from around 2.18 to over 2.2. The HTLs of a third group, shown in green (including Brazil, Chile, South Africa and several countries in Southern Europe), have risen further, from around 2.28 to 2.33.

By contrast, HTL in the world's wealthiest countries (shown in purple)—including those in North America, Northern Europe and Australia—was extremely high for most of the study period but decreased slightly starting during the 1990s, going from around 2.42 to 2.4. A fifth group of small, mostly island countries with limited access to agricultural products (shown in yellow, including Iceland and Mauritania) has seen more dramatic declines, from over 2.6 to less than 2.5.

These trends closely correlate, it turns out, with a number of World Bank development indicators, such as gross domestic product, urbanization and education level. The basic trend, in other words, is that as people become wealthier, they eat more meat and fewer vegetable products.

That has translated to massive increases in meat consumption in many developing countries, including China, India, Brazil and South Africa. It also explains why meat consumption has leveled off in the world's richest countries, as gains in wealth leveled off as well. Interestingly, these trends in meat consumption also correlate with observed and projected trends in trash production—data indicate that more wealth means more meat consumption and more garbage.

But the environmental impacts of eating meat go far beyond the trash thrown away afterward. Because of the quantities of water used, the greenhouse gases emitted and the pollution generated during the meat production process, it's not a big leap to speculate that the transition of huge proportions of the world's population from a plant-based diet to a meat-centric one could have dire consequences for the environment.

Unfortunately, like the garbage problem, the meat problem doesn't hint at an obvious solution. Billions of people getting wealthier and having more choice over the diet they eat, on a basic level, is a good thing. In an ideal world, we'd figure out ways to make that transition less damaging while still feeding huge populations. For example, some researchers have advocated for offbeat food sources like meal worms as a sustainable meat, while others are trying to develop lab-grown cultured meat as an environmentally-friendly alternative. Meanwhile, some in Sweden are proposing a tax on meat to curb its environmental cost while government officials in the UK are urging consumers to cut back on their demand for meat to increase global food security and to improve health. Time will tell which approaches stick.

In the meantime, simply keeping track of the amount of meat we're eating as a society via HTL could provide a host of useful baseline information. As the authors write, "HTL can be used by educators to illustrate the ecological position of humans in the food web, by policy makers to monitor the nutrition transition at global and national scales and to analyze the effects of development on dietary trends, and by resource managers to assess the impacts of human diets on resource use."

In other words, monitoring the intricacies of our middling position on the food chain may yield scientific fodder to tackle problems like food security, obesity, malnutrition and environmental costs of the agricultural industry. A heavy caseload for a number that ranks us on the same trophic level as anchovies.

Joseph Stromberg | | READ MORE

Joseph Stromberg was previously a digital reporter for Smithsonian.