We welcome Zach Throckmorton, of Lincoln Memorial University, as our first guest blogger . . . click for his bio, or go to the “Who we are” tab.

When did the Anthropocene begin? It is abundantly clear that those of us living today have an enormous impact on the living world around us. But since when are humans different than other larger-bodied mammals? When we integrate the archeological record with ecological theory, we can peer into the past to see how people interacted with the environment in ancient times.

The most challenging course I took while a grad student at UW-Madison with Noah Theriault was Animal Population Dynamics. I struggled with the math intellectually, but reading article after article of hard, objective demographic data illustrating how modern humans can so dramatically affect other animal populations was emotionally harrowing. Stiner et al.’s seminal 1999 Science paper shows the utility of using humanity’s ecological footprint to better understand past growth of our own populations. The authors sought to draw attention to how the need to feed in a degrading environment can spark novel behavioral innovations – like using nets to catch birds when there are no tortoises to eat. But their focus was on measuring human population growth – not measuring population declines in other species.

Their archeological data are unambiguous. Humans occupied the Israeli site of Nahal Meged, Galilee, fairly continuously from about 200,000 to 10,000 years ago. Table 2 in the Stiner et al. paper presents the bad news for tortoises: at 200,000 years ago, tortoises were abundant, and as easy, delicious prey, were a preferred food for humans. By 10,000 years ago, less than a third of the small prey taken at Nahal Meged were tortoises. Concurrently, birds (just as tasty but much more difficult to catch) were a negligible component of small-bodied prey taken at Nahal Meged, but by 10,000 years ago, a third of the small-bodied prey were birds. Humans not only switched prey from tortoises to birds: they also started eating smaller and smaller tortoises. Figure 4 in Stiner et al. shows the dramatic reduction in tortoise skeletal remains at the site: the tortoises taken 10,000 years ago were only two-thirds the size of tortoises taken 200,000 years ago. In animal population dynamics, this process is described by the Lotka-Volterra differential equation:

Where y is human hunting pressure, and x is for dinner

This equation predicts how quickly an animal population will decline given how much of it is eaten and how quickly it can reproduce. Tortoises do not reproduce quickly, so their populations are particularly susceptible to hungry humans. If the human population is growing rapidly, the tortoise population shrinks even faster – as evidenced by fewer and fewer larger, older tortoises (that all got eaten).

There are many variables that can affect how big animals can grow that have nothing to do with humans – like climate change. But importantly, Stiner et al. showed that factor was unlikely to play a role because this particular area’s ecology was relatively static during this time frame. This scenario should sound eerily similar, as it the same as in many areas of the world with many of the animals we consume. Fisheries on the verge of collapse are one of the more glaring examples.

If ancient humans living in Israel were hunting tortoises to near extinction about 25,000 years ago, then when did the Anthropocene begin? Modern humans inarguably have an unprecedented and disproportionate influence on the earth’s ecosystems today (at least for vertebrates – we cannot hope to match the effects that, say, photosynthesizers had on the planet). But since when are humans so different that we would consider naming a geological epoch after ourselves? I explored this question my first year of graduate school at the University of Indianapolis with my adviser John Langdon and colleague Laurah Turner. We combed the literature and came to the conclusion that the human footprint on the planet started becoming remarkable in the Middle Paleolithic. By the Upper Paleolithic, humans were causing serious, varied disturbances – and a lot of large animals start going extinct throughout the world.

While the Overkill Hypothesis is controversial, I cannot imagine humans played absolutely no role in the Quaternary Extinction Event. Though not considered a mass extinction event, 80% of the large mammal genera in the Americas and Oceania went extinct. European big mammals fared better, with less than a third of these genera disappearing. And African large mammals were almost unscathed, with less than 5% of them becoming extinct. Perhaps having evolved alongside our ancestors, when there were not many of them, as they first mastered stone tool use, fire, and then increasingly complex technologies, the African large mammals adapted to the increasingly substantial predatory pressure people posed. To this day, many large African mammals counterattack rather than flee when confronted by humans – nothing short of a tank would embolden me to stand down a charging bull elephant. American large mammals, however, first faced fully modern humans with atl-atls and other advanced technologies and behaviors – and stood no chance against our onslaught.

Our hunting technologies continue to become more and more efficient. And there continue to be more and more humans. Humans are unusual mammals in that we are able to extract nutrition from every trophic level and convert it into more humans.

From “Lisa the Vegetarian,” episode five of The Simpsons’ seventh season

Large, slowly reproducing mammals that we love to grill are increasingly expensive as they become comparatively less common like those tasty Israeli tortoises. From my paleoanthropological perspective, the Anthropocene began with the Quaternary Extinction Event.

If there’s any hope at all for not degrading the planet to the point where we ourselves become extinct, it’s in the Lotka-Volterra equation. We have to spread the heavy pressure we impose on other species widely so that individually, they don’t get stamped out of existence like the dodo – a large, slowly reproducing and undoubtedly delicious beast. And we’re best off consuming rapidly reproducing animals. Fortunately for us, there is a group of animals that is both speciose and characterized by high rates of reproduction: insects.