Endurance Running vs. Diving: Which Came First?

New study takes a land-and-water perspective on the evolution of our exceptional human stamina

To the point

• Humans have remarkable endurance: Unlike other apes, humans have a talent for endurance running, long-distance swimming, and breath-hold freediving.
• Human freediving ability: The typical human diving pattern falls within the range of shallow-diving, semi-aquatic mammals, showing a striking similarity to the bimodal diving range of sea otters.
• Bone mass and buoyancy: Buoyancy control is key to shallow diving, and shallow-diving semi-aquatic mammals have "heavy bones" compared to fully terrestrial mammals. Variation in hominin bone mass may reflect different niches: heavy-boned populations, such as earliest H. erectus from Java, may have foraged underwater, while lighter-boned populations focused on hunting and gathering on land.
• The "dive first, run later" hypothesis: Environmental pressures around three to two million years ago led coastal Homo to breath-hold dive for aquatic resources, selecting for increased bone mass and improved cardiorespiratory function. The latter adaptation may have helped more lightly built populations to develop endurance running and to live at high altitudes.

A new study combines palaeoanthropology and diving physiology to address a fundamental question in human evolution: why did humans evolve their exceptional aerobic endurance? Did our ancestors begin endurance-running terrestrial prey to exhaustion, or did breath-hold diving for aquatic resources also play a key role?

Drawing on comparative physiology, anatomy, paleoecology and paleoanthropology, researchers Josephine Joordens and Erika Schagatay propose a new "dive first, run later" hypothesis. In their study, they challenge and modify the popular endurance running hypothesis, arguing that the origin of human stamina cannot be understood from land-based foraging alone. "When studying the origin of human endurance and the evolutionary history of the Homo sapiens lineage, it is imperative to take not only endurance running, but also endurance diving for food, into account," they argue.

A new view on human endurance

Humans are unusual among primates. Not only are we capable endurance runners, we are also strong long-distance swimmers and skilled breath-hold divers. Modern populations of freedivers, such as the Ama and the Sama-Bajau, demonstrate that humans can repeatedly dive for hours to hunt fish, gather shellfish and other aquatic resources.

This form of repeated breath-hold diving is described in the study as "endurance diving": making repeated dives with short breathing pauses at a regular pace in order to minimise recovery time at the surface and maximise time spent underwater where resources are available. Japanese Ama divers, for instance, gather shellfish such as abalone and turbo shells by repeatedly diving to shallow depths. A time-depth recording of two hours of a working shift by an Ama diver shows 50 dives to depths of around 8-10 metres, with 45 per cent of the time spent underwater. "This diving method enables individuals to work underwater for hours each day while holding their breath," says Erika Schagatay, a professor of animal physiology and a specialist in human performance in hypoxic environments, such as breath-hold diving and high-altitude environments.

Challenging the endurance running hypothesis

The endurance running hypothesis, which was first put forward by Bramble and Lieberman in 2004, remains one of the main textbook explanations as to why humans became so different from other apes. According to this hypothesis, characteristics such as long legs, effective cooling mechanisms and increased aerobic capacity evolved as a result of early humans hunting terrestrial prey by pursuing animals over long distances.

Joordens and Schagatay do not dismiss the endurance running hypothesis outright. Instead, they argue that this explanation may be incomplete. Their "dive first, run later" hypothesis considers both running and diving and could provide a more comprehensive explanation of the diverse locomotion and foraging strategies observed among contemporary hunter-gatherers. "Our study provides a balanced land-and-water perspective on human evolution," says Josephine Joordens, a professor of hominin palaeoecology and evolution. "A combination of land-based foraging and foraging in water close to the shore by shallow diving could have shaped the multifaceted humans we are today."

Endurance diving as a gateway

Endurance diving requires enhanced respiratory and cardiovascular capacity, as well as the ability to pace breathing and breath-holding efficiently. When a person is only breathing half of the time, they must breathe twice as much when they can. Avoiding the build-up of lactate is essential. The researchers argue that this diving-related ability to pace effort and manage oxygen could have started off the evolution of the cardiorespiratory stamina required for long-distance running.

They also highlight an unexpected link between breath-hold diving and tolerance of high altitudes. Both activities involve hypoxic, or low-oxygen, conditions. An effective diving response helps to conserve oxygen during dives, while traits such as a large spleen can increase blood oxygen content in both diving and high-altitude environments. This is the first study to place these physiological similarities between breath-hold diving ability and high-altitude tolerance in a human evolutionary context.

Heavy bones - an adaptation to diving in shallow water

The study also revisits one of the most notable features of many hominin fossils: high bone mass, also known as "heavy bones". In the case of fossils belonging to groups such as Homo erectus and Neandertals, this has often been attributed to heavy physical loading and intense activity during life. Joordens and Schagatay draw attention to comparative data from terrestrial, shallow-diving and deep-diving mammals. These data show that increased bone mass can improve buoyancy control during shallow diving but reduce running efficiency. This suggests that populations of early Homo with heavy bones may have evolved high bone mass not through physically demanding terrestrial activity, but because heavier bones helped them to dive more efficiently in shallow coastal waters.

Variation in hominin bone mass may therefore reflect different ecological niches. Heavily built coastal Homo populations, such as the earliest Homo erectus from Java, may have included underwater foraging in their repertoire, whereas more lightly built Homo populations may have relied more on running and land-based hunting and gathering.

Different populations, shared human abilities

The paper also refers to recent DNA modelling results indicating that all modern humans evolved from a merger of two ancient populations which split apart very early on. "We suggest that the remarkable cardiorespiratory fitness and diving as well as running abilities of modern humans could have resulted from a merger between populations specialising in endurance diving and endurance running, leading to who we are today," says Joordens. "We can all learn endurance diving and running to some extent, but some may have more talent for running - and others for diving efficiently." This variation in abilities may have helped humans adapt to different environments and contributed to the successful global dispersal of our species.

Testing the "dive first, run later" hypothesis

The authors emphasise that, despite being incomplete and biased, the hominin fossil record remains an important archive of human evolution, particularly when combined with research in human physiology. Future research should evaluate the new "dive first, run later" hypothesis alongside the endurance running hypothesis, combining data and insights from palaeoanthropology and physiology.

The authors propose several approaches that could provide new ways of examining existing data. "For example, the external human nose may have evolved as an essential feature that enables shallow diving without flooding the nasal airways," says Schagatay. In future research, taking a combined land-and-water approach to available fossil data may lead to new functional interpretations that were previously overlooked.