This post is an excerpt from my upcoming book ‘Uncommon Cold: The Science & Practice of Deliberate Cold Exposure.’ It blends the experiences of my midlife crisis with the science of ice baths.
Uncommon Cold
CHAPTER 9
Evolution at Water’s Edge
Cold water is in our DNA
To understand autonomic responses to cold water immersion requires a narrative explanation of the historical selection pressures under which they evolved. For example, the wrinkles that appear on fingertips when they've been too long in the water are the result of vasoconstriction (Wilder-Smith & Chow 2013). However, these wrinkles have an evolutionary advantage beyond thermoregulation. They also improve grip, which may have aided our ancient ancestors when fishing with their bare hands.
According to a wonderful academic research book titled Human Brain Evolution: The Influence of Freshwater and Marine Food Resources (Cunnane & Stewart 2010) much of our ancient ancestors lives were lived along the coastline. There were at least two reason for it:
Only aquatic food resources (e.g., shellfish) can provide the omega-3 fatty acids that are necessary to support development of the enormous human brain, and these were not available in the grasslands of the savanna, and
During the Ice Ages, the human populations were squeezed between advancing equatorial glaciers and the coasts. As ice built up over the continents — including the equatorial glaciers of East Africa — sea levels dropped and humans moved into the areas of land that were uncovered by the receding coastline. The fossil remains of those ancient human communities are now underwater, but the consequences of those periods on human evolution were likely profound.
The Aquatic Ape Hypothesis
Humans have several unique anatomical features that distinguish us from the chimpanzees and bonobos with whom we share nearly 99% of our DNA. These features raise certain questions related to cold water immersion. For example, why do humans have:
· Nostrils that point down, while other apes have nostrils that point out?
· Less hair than chimpanzees and bonobos?
· Walk upright, instead of on all fours?
· Have large stores of subcutaneous fat like dolphins instead of low single-digit body fat percentages like apes? (Pontzer et al. 2016).
In the early 1960’s, a British scientist named Alister Hardy proposed to answer all of these questions at once by formalizing The Aquatic Ape Hypothesis (Hardy 1960). In summary, Hardy suggested that our anatomy evolved as an adaptation to aquatic lifestyles.
According to Hardy:
· downward facing nostrils allows ancient humans to dive without forcing water up their noses.
· less body hair streamlines swimming, & diving,
· walking upright facilitates wading in shallow waters,
· subcutaneous fat stores (just under the skin) would help keep humans warm and buoyant in cold water.
Proponents of Hardy’s Aquatic Ape Hypothesis point out that many of the unique characteristics of our anatomy resemble aquatic mammals like dolphins, whales, and manatees. Opponents point out that beavers and otters are both streamlined, and they have fur. That is, Hardy's skeptics argue that although we're the only apes with subcutaneous fat, there are lots of other creatures besides whales that have it, too. And walking upright would alsp be an advantage for hunters in the African grasslands, not just for foraging for shellfish with our heads above water.
The arguments opposing the Aquatic Ape Hypothesis are not 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?”
Evolution in cold equatorial waters
Hardy suggests that early hominids lived at the water's edge, and that our ancient ancestors evolved to wade, dive, swim, hunt, and forage along the beaches and streams coastal Africa.
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?
It is almost undoubtedly our enormous brains.
Keep reading with a 7-day free trial
Subscribe to Self-Actual Engineering to keep reading this post and get 7 days of free access to the full post archives.