The Evolution of Laughing and Crying

How have we humans come to be so skillful at smiling, laughing, and crying? Other notable human behaviors – reproducing, fighting, sharing, hunting –  have easily visible predecessors among most animals. But our repertoire of daily grins, laughs, and tears – except for some vaguely similar expressions among chimps, dogs, and rats – is unique. We express life’s joys and sorrows in ways that seem to have little ancestry.

But neuroscientist Michael Graziano proposes that we smile, laugh, and cry in useful mimicry of a protective, cringing reflex that is millions of years old.

In The Spaces Between Us: A Story of Neuroscience, Evolution, and Human Nature (2018), Graziano describes his team’s years of research at Princeton on how the brain monitors the personal space around us. This flexible buffer zone can extend out to the edges of the car we are driving or to our child who is leaning over a ledge. The buffer also shrinks to the physical closeness we allow with those we trust and even disappears altogether for pair bonding and sex. The buffer is a protective, not a social space. “Personal space is all about the zone where you keep people out, not the zone where you invite people in” (Kindle location 472).

Cringe (

So where do smiling, laughing, and crying come in? Such expressive reactions are rooted in an ancient cringe posture that people still take on when their protective zone is suddenly and dangerously threatened – by seeing a stone thrown at them, for example. The posture reflects the brain’s first priorities: protect the eyes and the abdomen. “The forehead is mobilized downward and the cheeks are mobilized upward, dragging the upper lip with them.” As a result, the teeth are exposed. Hands cover the abdomen, the body hunches down, shoulders rise.

Smiles (Mount Pleasant Granary)

We think of a smile as being about teeth, but the display of teeth is only a consequence of the cheeks lifting upward to protect the eyes. Still, the sight of this wincing “smile” may have reassured an early enemy that the individual in the cringe posture was not a threat. But the potential victim learned even more: that the facial expression could be imitated, mimicked, in order to ward off injury, to play it safe. Millions of years later, we smile.

Graziano states his point carefully. “…[T]o be clear, the human smile is not a defensive cringe. When you smile, you are not thereby protecting your eyes from a flying stone. You’re not expressing fear. You’re not anticipating an attack. But the evolutionary precursor of a smile is a defensive cringe that protects the eyes in folds of skin. A smile is an evolutionary mimic” (2255).


Laughter (

While the smile mimics a gesture that might have headed off a conflict before it started, laughter may have emerged as a way to prevent harmless play-fighting already in progress from getting too serious. Graziano connects laughter with tickling. When a child is tickled, the hand of the tickler moves into the child’s protective space, the cringe reaction begins to sound the alarm, the hand reaches an area of sensitive skin and “the touch evokes a full-blown laughter…an entire collection of alarm shrieks, defensive blocking and retracting, a pursing of skin around the eyes, upward bunching of the cheeks, upper lip pulling up, and secretion of tears”(2316). Laughter evolved from such an alarm reaction that tells a play-opponent that yes, you’ve touched me, touché, now that’s enough. Like the smile, laughter gradually became a social signal, read by others, mimicked by those who want to signal their good-natured agreeableness.

Graziano acknowledges that such speculation does not explain the many types of laughter – or the nature of humor itself. But it does suggest why, after the long road of its evolution, full and hearty laughter shares many of the facial markers of the defensive cringe.

Crying (youtube)

Crying, unlike smiling and laughing, adapts the cringe response to the loser’s need for friendly resolution after an all-out fight is over.  After an attack, a primate victor often comforts the loser. The loser’s cringing, moaning, and tears signal not only surrender but a plea to restore amity. After a million years of such reactions, we mimic the post-drubbing defensive cringe as a way to express pain and ask for consolation – even when we are crying alone.

Graziano’s book is very clear, very engaging, and at times very personal. And I value knowing how laughter and tears both link us to early ancestors while also displaying such an evolutionary distance from the original reflex.

Evolution for a Warmer Climate

The climate of the next few centuries “is expected to change 10 to 100 times faster than in the recent geological past.” Slowing this disastrous shift is one struggle. Another is figuring out how to help earth’s organisms to survive it. Humans have long maneuvered evolution to breed plants and animals for their own use. But as the earth grows warmer, understanding and experimenting with how species adapt to change is taking on a more ambitious, long-term purpose.

Animals and plants are responding to current climate changes in two ways. They adjust within the capacity of their DNA—plasticity, as it’s called—and they adapt by changing genetically. They demonstrate plasticity when birds breed and plants flower earlier as spring comes sooner. Animals show flexibility when they migrate towards cooler poles and higher elevations. Many species that scientists had considered doomed have shown greater flexibility than expected, but such plasticity has its limits.

Genetic changes—true evolution—are profound but also less adjustable in the short term. These are changes that can enable a species to resist new diseases and to thrive in new environments. The species that have the best odds for making such  evolutionary leaps are generally those with short lives (and therefore frequent reproduction), many off-spring, genetic diversity, and mobility.

Copepods off the west coast show some flexibility to water temperature but don't migrate enough to make larger genetic adjustments. (

Copepods off the west coast show some flexibility to water temperature but don’t migrate far enough to make larger genetic adjustments.

A case in point: The shrimp-like copepod swims off the west coast all the way from Mexico up to Alaska. That range of water temperatures might suggest that copepods would have no trouble adjusting to warmer water if they needed to. But the local populations are acclimated only to their local temperature and they don’t travel far enough to breed with other copepods that can handle warmer oceans. They are stuck within a limited plasticity.

Purple sea urchins are a different story. They must cope with the increasing acidity in the ocean that is one effect of a warming climate. Like the copepods and temperature, sea urchins in different parts of the ocean tolerate their local acidity. But the sea urchins are better off than the copepods because, essentially, sea urchins are more sociable. They are more likely to migrate, interbreed, and adapt genetically to higher levels of tolerance.

Purple sea urchins move around and intermingle, making them good candidates for genetic changes that will help them tolerate the ocean's rising acidity.  (

Purple sea urchins move around and intermingle, making them good candidates for genetic changes that will help them tolerate the ocean’s rising acidity.

Many species of animals and plants, like the copepods, will be unable to adjust enough to survive. So humans are beginning to step in. Conservation groups are connecting wilderness areas so that migrating species aren’t cut off by highways, cities, suburbs. One example are the Yellowstone to Yukon Conservation Initiative corridors between wild landscapes that run from Yellowstone Park to northern Canada.

In more active interventions, scientists have moved the seeds of trees in order to acclimate them to new environments. Animals too have been transported in order to change their genetic strain (though not yet for climatic reasons). When Florida’s panther population dropped below 30 in the 1990s, eight females that were brought from Texas created enough genetic variation to overcome the effects of inbreeding and multiply the population.

For now, scientists are mostly gathering information. How much can organisms adjust before they die off? Which necessary changes are genetic and therefore relatively slow? And—a devilish question— which species should we try hardest to save? The ones most at risk? Or those most likely to survive? The popular animals like lions and elephants? The ones that carry out key functions in the survival of other species, like bees?

Such interventions and assessments reassure and unnerve me at the same time. As the climate worsens and the urgency grows, as the effort to save species scales up, imagine the conflicts that will emerge. We have seen the debates over GMOs, carbon capping, sea coast construction. Imagine the political feuds and violence of the future when temperature and rainfall have shifted so much that it’s time to commandeer new land for farming, to organize globally to select animals and plants for survival, to abandon regions that are turning to desert and floodplain, to allocate water to some communities of species and not others. As the stakes get higher, the human role on the planet will grow more urgent and potentially more dangerous.