Ch 7: Human Breath-Hold Diving Ability Suggests a Selective Pressure for Diving During Human Evolution (pp 120 - 147)
in: Was Man More Aquatic In The Past?
Fifty Years After Alister Hardy Waterside Hypothesis Of Human Evolution
Eds. Vaneechoutte M., Verhaegen M., Kuliukas A.
eISBN: 978-1-60805-244-8, 2011.
Modern humans are generally considered to be fully terrestrial, yet display a range of activities involving breath-hold (apneic) diving, including sustained harvest diving, spear-fishing, recreational free-diving and competitive apnea for duration, distance or depth. Via harvest diving, involving repeated diving with half of the time submerged for several hours per day, groups in South East Asia obtain a considerable amount of catch. The physiological basis for such repeated diving involves i) conscious breath control, ii) an efficient diving response, diverting stored oxygen to the heart and brain, and iii) adequate thermal insulation. Another contribution to the human diving ability comes from the spleen, which - by ejecting extra red blood cells into circulation - can enhance blood gas storage and carbon dioxide buffering capacity, a response typically found in seals.
Most striking among human aquatic activities is competitive apnea, with records of a period of 11 min 35 s in duration, the distance of 265 m in underwater swimming with fins, and a depth of 124 m in deep-diving with fins. Without fins, the distance of 218 m and depth of 101 m have been achieved, performances in the range of marine mammals. This requires additional mechanisms to maximize gas storage, minimize energy expenditure, and enhance conscious tolerance to asphyxia, involving e.g. increase lung volume, baseline hematocrit and spleen volume, and means to cope with the increased pressure. While it takes both inherent predisposition and training to achieve such record results, most healthy humans can, after some practice, make voluntary apneas of 3-4 min, swim a distance of 50 m under water and reach depths of 20-30 m, which may be unique among terrestrial mammals.
Human superior harvest diving and competitive diving capacity may suggest a selective pressure for diving during some time period of human evolution.