Cold water immersion likely shaped our evolution

Updated: Aug 28

The Aquatic Ape Hypothesis suggests our ancient Mothers gave birth in cold water

Will the evolutionary missing link be found in the water?

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.

Why, for example, do humans have less hair than chimpanzees? Why do we walk upright? And why are humans beings the only primates with fat just beneath the skin?

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.

  • 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.

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. They 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.

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?

Cold water immersion might be in our DNA

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.


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.

Geography and human evolution

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. Nonetheless, it is 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 geography of human evolution must have included cold water.

While the principal distinguishing feature of human beings is their large brains that allow them to form complex social networks, 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 homo sapiens.

But 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). Moreover, at 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).

The Aquatic Ape Hypothesis suggests that our ancestral Mothers would have sought out the same relief from childbirth pain that modern Mothers do, and given birth in the water. If that singular practice conferred upon human beings the evolutionary advantage larger brains, then it was water births that allowed us to become human.

And the streams and rivers in the East African metaphorical Garden of Eden were the first human women gave birth must've been cold, given the hydro-geography of that region at the time.

That means that we evolved to be born in freezing cold water.

As I told Dean Hall:

If it's true that we are all born into the cold water, then there must be something about the experience of the ice bath that brings up the original trauma of childbirth for us.
It's no wonder that you feel an emotional unburdening from the Forge.
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.

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


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