Living in a dangerous world
This study is not the first evidence that ancient hominids dealt with lead in their environment. According to a 2018 study, two Neanderthals living in France 250,000 years ago were exposed to lead as young children. At the time, these were the oldest known examples of lead exposure (and they are included in the recent study by Joannes-Boyau and colleagues).
Until a few thousand years ago, no one melted silver, plumbed public baths, or released lead fumes into car exhausts. So how were our hominid ancestors exposed to the toxic element? Another study, published in 2015, showed that Spanish caves occupied by other groups of Neanderthals contained enough heavy metals, including lead, to “meet current ‘contaminated soil’ standards.”
Today we think of lead primarily in terms of human-caused pollution. So it’s easy to forget that it also occurs naturally in rock and soil. If this were not the case, archaeologists would not be able to use lead isotope ratios to determine where certain artifacts were made. And some places – and certain rock types – have higher lead concentrations than others. Several common minerals contain lead compounds, including galena or lead sulfide. And the type of lead exposure documented in Joannes-Boyau and colleagues’ study would have occurred at an age when small hominids were very prone to putting stones, cave dirt, and other random objects into their mouths.
Some of the fossils from the Queque cave system in China, which included a 1.8 million year old gorilla-like ape called Black Gigantopithecushad lead levels above 50 parts per million, which Joannes-Boyau and colleagues describe as “a substantial lead level that could have triggered developmental, health, and perhaps societal impairments.”
Even for ancient hominids that did not live in caves filled with lead-rich minerals, wildfires or volcanic eruptions can also release lead particles into the air, and erosion or flooding can result in lead-rich rocks or sediments buried in water sources. If you’re an Australopithecus living upstream of an outcrop of lead-rich mica, for example, erosion could spread poison into your drinking water, or into the drinking water of the gazelle you eat, or into the root system of the bush you get those tasty berries from….
