A brief history of blood, sweat and tears
So humans are a peculiar species. You probably knew that. What you may not have realized is how many specific traits and behaviors are uniquely human.
We're not just big-brained featherless bipeds with special instincts for language, tools, and culture. We're also the only creatures who sing from the ground, sing and dance together, bury our dead, point declaratively, enjoy spicy foods, blush, and faint (not to mention all of our weird sexual practices). We have the least symmetrical brains, the most dependent babies, and the fastest and most accurate overhand-throwing skills.
In his famous speech, British Prime Minister and orator Winston Churchill condensed his interpretation of human uniqueness into “Blood, Toil, Tears, and Sweat”. Churchill's call to action solicits cooperative national efforts that transcend political differences. In a situation of extreme national distress, that’s his offer to achieve “victory at all costs”. “All we got”, if you will.
In a broader sense, blood, sweat and tears are a triad that makes us unique as humans. They are what we are left with when stripped down of political narratives and ideologies. Blood, sweat and tears are both our superpowers and kryptonite. I wanted to peel the layers on what we possess that no one else does on this planet.
Blood: fear and insight
In “Nine Pints”, Rose George examines the unique biology of blood and tradition surrounding it. “The iron in our blood comes from the death of supernovas, like all iron on our planet,” she writes. “This bright red liquid contains salt and water, like the sea we possibly came from.” George charts the distance that our blood travels in the body every day. Some twelve thousand miles, “three times the distance from my front door to Novosibirsk.”
Ancient people knew none of this biology. But they were certain of blood’s importance and fascinated by its mystery. For them, blood was something hidden. Visible only when flowing from a wound, or during childbirth, miscarriage, and menstruation. So it became a symbol both of life and of death.
In medicine, the most appreciated feature of blood is the ease of access. A pinprick of a finger yielded a drop on a slide that, under the microscope, revealed a world of cells of different shapes, sizes, and colors. Looking at blood this way was like solving a puzzle. Inspecting the configuration of the nucleus and the cytoplasm for clues on the path to a correct diagnosis.
Blood is figurative and emotional, too: our blood “boils” when we’re angry, “chills” when we’re afraid, “curdles” when we’re threatened. Such primitive associations appear to be impervious to advances in scientific understanding. In Japan, blood types now underpin a pseudoscientific philosophy of personality types. A little like astrological signs. Type A’s are considered perfectionist, kind, calm even in an emergency. B’s are eccentric and selfish, but cheery. O’s are both vigorous and cautious while AB’s, obviously, are complicated.
For millennia, the human body was understood as a vessel for a quartet of liquids: yellow bile, black bile, white phlegm, and red blood. Each corresponded to one of the four classical elements—fire, earth, water, and air — from which it was thought everything in the cosmos was made.
Bloodlines. Blood brothers. Blood feud. We still think of blood as what makes tribal identity cohere. The inquisitors in Spain defined race by blood, as did Southern slave owners and Nazi eugenicists. We fear blood, still, despite our science and understanding, and we look to blood to tell us who we should fear.
Before long-range projectile weaponry, there were only two ways to secure meat. Either by scavenging the leftovers of mightier beasts or by running down their own prey. Humans occupied the latter ecological niche thanks to two great advantages of bipedalism.
The first advantage is in how we breathe. A quadruped can take only a single breath per locomotive cycle. Its chest must absorb the impact on the front limbs. We can choose other ratios, and pace our energy consumption.
The second advantage is in our extraordinary ability to regulate body temperature. This allows us to do what lions cannot. Run long and hard in the noonday sun. It all comes down to sweating.
The two large animals used for transport perspire profusely compared to other quadrupeds. In one hour, a horse can lose about 100 grams of water per square meter of skin, and a camel can lose up to 250 g/m2. Duck soup for humans. We shed 500 g/m2, enough to remove between 550 and 600 watts’ worth of heat.
Peak hourly sweating rates can surpass 2 kilograms per square meter. The highest reported short-term sweating rate is twice that high. In the animal kingdom, we are the superstars of sweating.
And we have another advantage when we lose water. Humans can tolerate considerable temporary dehydration. In fact, the best marathon runners drink only about 200 milliliters per hour during a race. These advantages allowed our ancestors to become unrivaled as diurnal, high-temperature predators.
They could not outsprint an antelope. But during a hot day, they could dog its heels until it finally collapsed, exhausted. Documented cases of such long-distance chases include some of the fleetest quadrupeds. In North America, the Tarahumara of northwestern Mexico could outrun deer. In Australia, some Aborigines would outrun kangaroos.
In the race of life, we are neither the fastest nor the most efficient. But thanks to our sweating capability, we are the most persistent.
Tears: reverse dominance and social support
Humans aren't the only species whose eyes occasionally fill up with fluid. Nor are we the only species to wail in distress. But we are the only ones who unite tears and noisy crying together in a single behavior. Tears are a fascinating, understudied puzzle, ripe with insight into the human condition.
Tears don't have any medicinal healing powers. They don't serve an excretory function, i.e., by flushing toxins or stress hormones out of the body. Weeping is a behavior that we, as biological organisms, enact for a specific purpose. Despite our celebrated self-awareness, we are oblivious to our reasons for crying.
Tears represent a behavior rather than a symptom. In particular, they're a social behavior. Something we evolved to do because of their effects on the people around us. Tears are a signal. But Nature doesn't evolve new signals just for the hell of it. In fact, Nature is fairly conservative in this regard. So for a new signal to evolve, there has to be a good reason. Some unique communicative agenda not satisfied by the existing vocabulary.
Kevin Simler suggests that we evolved weeping to prove to third parties when we are victims of aggression. To seek refuge from, and "tattle" on, aggressors. Unlike other submission and distress signals weeping leaves the victim with a wet face, red/puffy eyes, a runny nose, and a heaving chest. Signs that remain visible (and audible) for many minutes after a conflict. This is ideal for running off and soliciting help from others who may be out of earshot and/or direct sight.
The hypothesized original function of weeping was to serve as a submission and a distress signal at the same time but addressed to two different receivers - the aggressor and the helper. Tears, in this theory, are a political act.
In any other species, wearing a signal that advertises, "I recently lost in a dominance challenge," is strict liability. An invitation for others to pile on. But humans are different. For us, wearing a badge of surrender is also something of an asset. It plays into the instincts of third parties to help those who have been victimized.
We have strong social norms against aggression, and a unique eagerness to support the underdog. This whole suite of attitudes and reactions is called a reverse dominance hierarchy. This goes a long way toward explaining our instincts towards social norms and cooperation.
Tears are inherently a piece of social technology. A device for coordinating the tradeoff between dominance and social support. And this invention turns out to be useful in a variety of scenarios. Whenever people are rewarded for humbling themselves and/or opening themselves up for connection, we shouldn't be surprised to find tears. We survive not as individuals but as social creatures, soldered together with tears.