A duo goes against the tide to explain an origin of human endurance

Two researchers may have opened floodgates on the debate over why humans can run marathons, swim the English Channel or dive a hundred meters and back on a single breath and their ape cousins can’t. Humans evolved endurance for feats like these not just by running down prey on the African savanna, but also by diving for food in lakes or coastal waters, the duo propose September 17 in PaleoAnthropology. The hypothesis adds complexity to a decades-old theory that puts the drivers for evolution exclusively on land.

But it coexists with a history of pushback for any water-related ideas. The work is causing ripples among anthropologists. In 1960, researchers came up with what’s been called the aquatic ape or waterside hypothesis, which suggested that our ancestors evolved longer legs and other adaptations from swimming for their suppers in watery habitats.

Popularized in media accounts but not adequately vetted in peer-reviewed journals, the idea was shunned by the scientific community as additional fossils pointed away from a life in water. More recently, the dominant theory has been that it was landlocked human ancestors who gradually developed our remarkable endurance. Yet evolutionary anthropologist Josephine Joordens, a self-professed “water person” who trained as a marine biologist, had long wondered whether coastal life was vital to the evolutionary process, because it provides easy access to both water and land resources.

Joordens combined forces with Erika Schagatay, a physiologist at Mid-Sweden University in Östersund, to formulate what they call the “dive first, run later” hypothesis. Schagatay — herself a freediver — has spent decades observing and monitoring modern sea foraging people such as the Ama in Japan and the Sama-Bajau in Southeast Asia. Joordens studied fossil evidence and combed the literature about aquatic activities.

Our evolution “was likely a very complex and very dynamic process,” says Joordens, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. They propose some Homo species wound up shallow-water diving repeatedly about 2 million to 3 million years ago, much the way the Sama-Bajau do today. These people spend four to six hours per day repeatedly diving several meters deep to catch fish and collect shellfish and other food.

They evolved bigger spleens than their non-diving counterparts and, it seems, enhanced respiratory and cardiovascular capacity. They have the ability to “pace” breathing periods and breath-holding to avoid fatigue. In our ancestors, that could have paved the way for the cardiorespiratory stamina needed in modern endurance running, Schagatay says.