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How Cold Water Immersion Shaped Human Evolution

Updated: Jan 23

Our ancient Mothers likely gave birth in cold water


  • How come human babies are born knowing how to swim, but they don't learn to walk for 10-12 more months?

  • Certain anatomical features of human beings are more similar to aquatic mammals like dolphins, whales, and manatee than they are with Chimpanzees, suggesting that Homo Sapiens evolved near and in the water.

  • The equatorial glaciers of East Africa suggest that the streams in which our ancient grandmother's likely gave birth were cold.

  • One woman in the United Kingdom labored in a cold bath. She reported an easy childbirth and excellent birth outcomes.

Evolution at the water's edge

There are several anatomical features that distinguish human beings from other primates with whom we share more than 95% of our DNA, and these features raise several curious questions. For example,

  • Why do humans have less hair than chimpanzees, bonobos, and gorillas?

  • Why do we walk upright?

  • Why are humans beings the only primates with fat just beneath the skin?

  • Why do human nostrils point down, while other apes have nostrils that point out?

A British scientist named Alister Hardy proposed The Aquatic Ape Hypothesis (Hardy 1960), to answer each of these questions. In summary, Hardy suggested that our anatomy evolved as an adaptation to aquatic lifestyles. He suggests that early hominids lived at the water's edge, and that our ancient ancestors evolved to wade, dive, swim, hunt, forage, and birth in the streams of East Africa.

According to Hardy:

  • Less body hair would streamline us for swimming & diving,

  • Walking upright would allow us to wade thru shallow waters with our heads above water, and

  • Fat just under the skin would help keep us warm and buoyant in cold water.

  • Downward facing nostrils would allow ancient humans to dive without forcing water up their noses.

Proponents of the Aquatic Ape Hypothesis point out that many of the unique characteristics of our anatomy are similar to dolphins, whales, and manatee -- i.e., other aquatic mammals. Opponents point out that beaver and otters are also streamlined, and they have fur. That is, Hardy's skeptics argue that, although we're the only primates with subcutaneous fat, there are lots of other creatures besides whales that have it, too. And that walking upright would be an advantage for hunters in the African grasslands, not just in foraging for fish.

A 16 minute video (below) provides a lovely summary of the both hypothesis and its detractors.

But none of the opposing arguments to the Aquatic Ape Hypothesis are convincing to me, because no one is really asking, "What makes humans different from beavers?"

A much more interesting question is:

Why are human babies born knowing how to swim, but not how to walk?

Human bodies expect cold water immersion

Almost everyone has an experiential understanding of the healing power of the water (e.g., Blue Mind by Nichols, 2015). Even those who do not enjoy swimming almost always appreciate the serenity and beauty of being at the beach.

The Aquatic Ape Hypothesis might explain the feeling of deep connection that some people feel to the water. If our ancestors were selected, under evolutionary pressures, to live along the shores, then it would make sense that we feel that ancient calling to the water.

It is sometimes said that Nature (and/or God, depending on your point of view) does not make mistakes. That is, every anatomical feature in the human body must serve some evolutionary purpose that increases chances of survival and sexual reproduction.

If that's the case, then what evolutionary purpose could the aquatic aspects of human anatomy possibly serve?

Allow me to suggest that is our enormous brains.

The principal distinguishing feature of human beings is their large brains that allow them to form complex social networks. Growing such a brain demands nutrient-dense foods rich in omega-3 fatty acids, and fatty fish are the best source of omega-3's available. So it makes sense that ancient hominids who were adapted to the water would secure more of the essential fatty acids necessary to construct healthy brains. For example, it may be that walking upright was an adaptation to wading in the water to spear or trap fish.

However, evolutionary biologists have failed to explain how it is that human women evolved to have a pelvis that would both allow them to walk upright and give birth to human babies with enormous skulls. The risks in childbirth, both to Mother and baby, of passing such a large brain through the birth canal must have put tremendous negative selective pressure on the first Homo Sapiens.

Even though the bones of the newborn skull are flexible and the human baby brain is highly underdeveloped (small) relative to how much it still needs to grow, the baby's enormous head is still difficult to birth. For our ancient grandmothers, the remedy for the unique difficulties of human childbirth was likely also found in the water. For example, experience with modern water births have demonstrated reduced pain, greater maternal satisfaction, and fewer medical interventions (Simkin & Bolding 2004), compared to births outside the bath (Young & Kruske 2013).

The Aquatic Ape Hypothesis suggests that our ancestral Mothers would have sought out in water births the same relief from childbirth pain that modern Mothers do, which would explain why baby's born with instinctive knowledge of how to swim would have an evolutionary advantage.

If an ancient practice of water births made it feasible for human beings to birth larger brains, then it was water births that allowed us to become uniquely human.

How cold was the water?

It's easy to forget that there are three mountain-top glaciers near the Equator in East Africa, where human beings are thought to have evolved -- even though we all remember that it was Mount Kilamanjaro in Tanzania that Wim Hof chose for his record-breaking, frigid hiking expeditions. So despite our expectation that human beings must've evolved in a hot place that was without winter, it must also be true that there was no shortage of streams and river beds fed by melting snow.

In short, the streams and rivers in the East African metaphorical Garden of Eden where the first human women gave birth must have been cold, given the hydro-geography of that region at the time.

The analgesic effects of cold water immersion have been well known, so it stands to reason that a cold water birth might relieve labor pains. One woman in the United Kingdom who was brave enough to try it reported exactly this. She reported that she bathed in a cold outdoor pool "while in early labour and had a very easy and quick birth" (Cool Swimming, Buckley 2022, p16). Moreover, more than one study has demonstrated that ice massage during birth labor is effective for reducing a pregnant woman's pain (e.g., Hajiamini et al. 2012):

... the results suggest that ice massage is a safe, noninvasive, nonpharmacological method of reducing labor pain (Waters & Raisler 2003).


Feeling called to the water

I had a phone conversation today with Dean Hall, the trauma therapist who cured his leukemia with cold water swimming. He asked me why he felt such a strong emotional release when he emerges from the Forge.

I told him, "I don't know for a fact, but I will share with you my speculation."

This is what I told him:

One of the things that has been very difficult to explain about deliberate cold exposure is an answer to the question "Why is an ice bath so important to human health, when you know our species emerged in the hot, equatorial climate of East Africa?" It's a particularly vexing problem, to explain why the benefits of cold exposure are not exclusive to those human beings who descend (more recently) from cold climates. The Aquatic Ape Hypothesis probably holds important clues.

That is, no matter whether your ancestors hailed from the North Sea (as mine did) or from the equator, the early evolutionary experiences shared by all human ancestors likely shaped our anatomy to need cold water immersion on a regular basis. Just like our bodies are evolved to expect exercise and we get sick if we're not getting enough of it, it is likely that we will experience less-than-optimal health if we don't get enough cold water immersion.

Whole-body, cold water immersion is in our ancient DNA.

As I told Dean Hall:

If it's true that our ancient ancestors were all born into the cold water, then there must be something about the experience of the cold water that brings up the original trauma of childbirth for us. It's no wonder that you feel an emotional unburdening from the ice bath. Something in your ancestral, evolutionary history is calling you to the ice bath, where you can relive your birth trauma, and resolve it from a position of control.


Deliberate Cold Exposure & Trauma

The psychological principle of "compulsion to repeat" claims that we become hard-wired by trauma to recreate the traumatic experiences in ways that allow us to resolve them. In that way, the experience of the ice bath might be a symbolic reliving of our birth trauma.

Dean told me that after swimming the entire length of the Willamette River in Oregon, he referred to the Willamette as "Mother River." Perhaps it is no accident that the Christian tradition of baptism in the water is sometimes characterized as being "born again."


About the Author

Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.

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