Joordens and Schagatay put breath-hold diving before running in the origin of human endurance

A diver who is at the surface for only half of a working period has to take in twice as much air while she can, and has to hold effort below the point where lactate accumulates ^[11]. Sustaining that takes respiratory and cardiovascular capacity plus the ability to pace breathing and breath-holding ^[11]. Joordens and Schagatay argue that this pacing ability could have started the evolution of the cardiorespiratory stamina that long-distance running requires ^[12]. "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 ^[3].

The measurements behind that pattern come from one working shift. Fifty dives in 120 minutes is one dive every 2.4 minutes ^[17]; 45 percent of two hours is 54 minutes underwater ^[18]; spread across the dives, that is roughly 65 seconds below the surface each time against about 79 seconds on it ^[19]. "This diving method enables individuals to work underwater for hours each day while holding their breath," said Schagatay, a professor of animal physiology whose work covers human performance in hypoxic environments ^[8]. One trace from one diver cannot show how a population of them works. What it does show is that the pattern is sustainable in a trained modern freediver.

High bone mass appears in many hominin fossils, and the authors reinterpret it as an adaptation to diving in shallow water ^[15]. The fossil record bears on that claim directly.

The comparison most open to testing is the altitude one. Breath-hold diving and high-altitude living both impose low oxygen; the diving response conserves oxygen during a dive, and a trait such as a large spleen can raise blood oxygen content in both settings ^[13].

Bramble and Lieberman's 2004 hypothesis derived long legs, effective cooling mechanisms and increased aerobic capacity from hunting terrestrial prey over long distances ^[4]. Humans are unusual among primates in being capable endurance runners as well as strong long-distance swimmers and skilled breath-hold divers ^[20]. "Our study provides a balanced land-and-water perspective on human evolution," said Joordens, a professor of hominin paleoecology and evolution ^[9]. A synthesis of existing comparative evidence does not weigh the energetic returns of the two activities against each other. What it can do is propose a sequence. "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," she said ^[10].