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Breath Control The diving reflex  All mammals have an automatic response to being submerged in (or falling into) water known as the 'diving reflex'. This autonomic reaction immediately ensures the animal holds its breath, reduces its heartbeat (bradycardia) and redirects oxygen laden blood to the brain and the most oxygen dependent organs (vasoconstriction). In fact, so effective is this mechanism, that a person or an animal doesn't even need to be fully submerged for it to take effect; it works just as effectively when the face is submerged or cold water is splashed on the forehead and around the eyes and nose. In Darwinian terms, this evolutionary adaptation makes sense, as it means any animal that falls into water won't immediately drown. Comparisons with other animals have shown that the diving reflex is more highly developed in aquatic and semi-aquatic mammals, as one would expect, and that human test subjects fared only slightly better than most terrestrial animals until further tests showed there was a big difference when volunteers who had had some previous breath holding training were used instead:
"When researchers began to use trained subjects they found a dramatic difference in the results. Bradycardia in face immersion in untrained humans reduces the heart rate by an average of 25%. In groups of experienced skin divers the average reduction is 45%. Among ethnic groups where diving is an important part of their daily activities, the response is even higher." [1] It should be noted that 'training' can be aquired by anyone in a very short time. All it takes is up to five breath holds spaced out by three minute intervals to establish a difference to our physiological response to submergence, and breath-holding could be prolonged by 160%. [2] Breath holding abilities  Newborn human babies are born with an automatic breath-holding reflex, which is why they can be immersed in water as soon as they are born. In baby swim classes, parents are usually encouraged to wet their baby's face before immersing them in order to activate the diving reflex. The breath-holding reflex, unlike the diving reflex, is generally lost if the infant is not introduced to water within the first 6-10 months, and has to be relearned.
Many non-aquatic mammal species can hold their breaths underwater if they are forced to, but they cannot voluntarily hold their breaths on a whim, as we can, although better studies are needed to confirm this. [3] Compared to terrestrial mammals, human beings do have superior breath-holding abilities. Erika Schagatay from the Department of Technology and Sustainable Development and Swedish Winter Sports Research Centre, has spent over twenty years researching human breath holding abilities among diving peoples around the world, including the Ama in Japan, the Hae Nyo in Korea and the Sea Nomads or Sea Gypsies in Indonesia, Phillipines and Burma. Her observations have led her to conclude: "The excellent diving performance of trained members of our species, in the range of several semi-aquatic animals, both concerning endurance and maximal performance, suggests a selective pressure for diving during some period in human evolution. It is difficult to understand how such specialized skills and responses could have evolved in an environment and a scenario not involving diving. While many of these features are present to some extent in other mammals, the combination and magnitude seem to be unique for divers. The basic mechanisms seen in marine mammals were present also in their terrestrial ancestors and refined by adaptation in varying degree to an aquatic environment. The apparent reserve capacity displayed by some competitive elite-trained divers may indicate that humans were more aquatic in the past, as suggested by Hardy, already 50 years ago." [4] Aquatic and semi aquatic mammals obviously have highly developed breath-holding abilities. Like them, and just like semi-aquatic birds or reptiles, we can override the signals to our brain that carbon dioxide is building in the blood and continue holding our breath for a varying amount of time according to our training and experience. Among all air-breathing animals, the record is held by the sperm whale which has been known to hold its breath for deep sea dives for up to ninety minutes, although they regularly dive for 20-30 minutes each time. Experiments with seals and porpoises have shown that they can be trained to dive and retrieve objects at different depths, and that they can calculate how long they need to hold their breath for according to the item that they are being asked to retrieve, consciously making a decision before they dive about how long they need to hold their breaths for. We also calculate how much oxygen we need on a single breath as this is something we do every day, whether we enter the water or not. Our breath holding abilities are a prerequisite for speech and song. We automatically control the amount of breath we need to utter a sentence or sing. The majority of terrestrial animals cannot do this and it is one of the reasons why they cannot speak [5] Human divers  Although we cannot hope to compete with the fully aquatic cetaceans, or even the almost fully-aquatic pinnipeds (seals, sealions, etc.), Erika Schagatay has spent enough time as a diving instructor studying free diving peoples that she notes we can compete quite well with several semi-aquatic species:
"Humans in general seem to be well equipped for repeated diving to depths of 5-20 m to engage in underwater harvesting for several hours per day, with at least half of the diving time spent actively working on the sea floor. This is similar to the normal diving activities seen in several species of successful semi-aquatic mammals such as the sea otter, beaver and manatee, as well as in species of diving birds and reptiles. Voluntary, conscious apneic durations of beyond 10 min and underwater swimming distances of beyond 250 m suggest a great reserve capacity expressed in the trained human, relative to what is necessary for productive underwater harvesting. Human deep-diving skills, achieved after training, include many productive dives to 30-40 m in one day, and single dives for maximal performance exceeding 100 m." [6] In recent decades we have seen an increase in the number and variety of human apneic diving competitions including maximum duration or depth on a single breath, either with or without fins and/or weights. The world record for no limits apnea free-diving for men was set by Herbert Nitsch from Austria in 2007 at 214 meters on a single breath, and by Tanya Streeter, USA, at 160 meters for women in 2002. The record for static apnea (holding one's breath under water while remaining still) is held by Stephane Mifsud from France (11 minutes, 35 seconds) for men, and by Natalia Molchanova, Russia, ( 09 minutes, 2 seconds) for women, "performances in the range of marine mammals," Schagatay says. "Thus after only a short period of organized competitions, human apneic diving is approaching limits previously seen only in semi-aquatic and aquatic mammals, such as seals and dolphins, and certainly not typical or even possible for fully terrestrial air breathers. This rapid record development does not yet seem to level off. Considering the fast development seen and the increasing popularity of the sport, it is clear that the limit of the human aquatic potential has not yet been reached." [7] Schagatay goes on to observe that the comparatively high age at which top results can be produced by competitive divers is atypical compared to other sports. (Natalia Molchanova was 53 years old when she tragically failed to surface from a deep dive in summer 2015.) Many Ama divers also remain fully active into their 90s. She notes that marine mammals are known for long life-spans not often seen in typical land dwellers. However, nobody is suggesting that the ancestors of homo typically swam to depths of 100 meters or more, or needed to hold their breaths for such long periods on a daily basis. Human ancestors would probably have spent much of their time harvest-diving for shell-fish and edible plants, or perhaps spear fishing. "Humans and some species of semi-aquatic mammals rely on lung oxygen for an important part of the total oxygen storage, suggesting that they are typically shallow divers in the sense that they rarely dive below perhaps 30 m, but with a reserve capacity for single deeper dives and longer durations." [8] "Such capacity could reflect that our ancestors were at some point in our prehistory possibly more advanced divers than e.g., the modern Ama, with diving patterns as in the sea otter and other benthic feeders. It is striking that the diving patterns in human harvesting and competitive divers combined closely mimic the bimodal diving activity range of the foraging sea otter, with serial short
dives to < 20 m, or longer and deeper dives to 40-50 m separated by extended recovery intervals, and in extreme cases dives to 100 m. In a group of 14 sea otters, only 5/12000 recorded foraging dives were 90-100 m, while 84% were< 30 m. Such diving behavior depends on several specialized features apparently co-evolved among various diving mammals, and our features suggest that trained humans could fit well among semi-aquatic mammals. [9] "These apparent aquatic adaptations may also be the background to some of the uniqueness of humans among primates, and among terrestrial mammals in general, e.g., vocal communication, body nakedness, a subcutaneous fat layer, upright position, fat babies, underwater vision (see Chapter 10), long lifespan, and a large brain with the need of marine fat sources for optimal development (see Chapter 2). Briefly, when human diving adaptations would stand alone as a phenomenon, that would be remarkable, but when supported by so many independent indications for an aquatic past, they become remarkably plausible." [10]
References: 1. Morgan, Elaine. The Aquatic Ape Hypothesis. Souvenir Press. p.144
2. Hentsch, U. and Ulmer, H.-V. (1984). Trainability of underwater breath-holding time, Int. J. Sports Med., 5, 343-7.
3. http://carta.anthropogeny.org/moca/topics/voluntary-control-breathing
4. Schagatay, Erika. Was Man More Aquatic in the Past? Chapter 7: Human Breath-Hold Diving Ability Suggests a Selective Pressure for Diving
During Human Evolution. Bentham ebooks, p.143
5. http://carta.anthropogeny.org/moca/topics/voluntary-control-breathing
6. Schagatay, Erika. Ibid. p.
7. Ibid.
8. Ibid. p.141
9. Ibid. p.142
10. Ibid. p.142-143
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