The human condition encompasses the unique features of being human. It can be described as the irreducible part of humanity that is inherent and not dependent on factors such as gender, race or class. (Wikipedia)
In the developed world, we live in the most peaceful, healthful time
in history. The murder and violent crime rate is dropping; we are
vaccinated against the most deadly diseases of previous generations; our
houses protect us from most storms; relatively few people go hungry.
The average lifespan is longer than it has ever been. Then why do we
walk around so anxious, so full of fear? The answer is not terrorists,
TV, Republicans, or Democrats. The answer is our legacy of ancient
fears, the result of having spent millions of years running from
predators. Our fear response is more influenced by the ancient species
we struggled to escape than any modern challenges. We live in a demon-haunted world.
Until not that many generations ago, Homo sapiens and our
primate ancestors found shelter under lean-tos, in caves, and up among
branches. Exposed and relatively defenseless, our predecessors stood a
good chance of being eaten by bigger, badder, species. For most of our
evolutionary history as primates, we were far more likely to play the
role of Big Mac than Big Man on Campus. Our ancestors evolved many
traits to help them escape that fate—if not forever, at least long
enough to reproduce and pass their genes along. These responses still
frame how our bodies work today, which would be great if we were still
being stalked by large cats. But Vegas performers notwithstanding, most
of us are not.
Nor was it just cats. Humans were eaten by giant hyenas, cave bears,
cave lions, eagles, snakes, other primates, wolves, saber-toothed cats,
false saber-toothed cats, and maybe even—bless their hearts—giant, predatory kangaroos.
Amazingly, these are just the predators that consumed our ancestors
during relatively recent history, the past 100,000 years or so. Go
further back in time, and the diversity of things that ate our kin goes
up (particularly given that our earlier, pre-hominin
ancestors were progressively smaller). Some predators, such as
leopards, ate many of our ancestors. Others, like crocodiles, komodo
dragons, or sharks, took their bites, but more opportunistically,
savoring the occasional human or proto-human the way one might enjoy
some special holiday treat. We were, in other words, their thanksgiving
turkey.
In those few places where large predators are still common, primates,
especially cute baby ones, are eaten with great frequency and alacrity.
When our species evolved, human children were special only in as much
as their hairlessness made them slightly easier to digest. Even today,
where humans live alongside predators, both children and adults get
eaten. Harry Greene, a herpetologist at Cornell University and one of a
handful of my colleagues more likely to be eaten by a wild animal than
to die of old age, and Thomas Headland, an anthropologist, recently
conducted a study of Agta hunter-gatherers in the Philippines. Harry was
excited to find that the Agta lived among a high density of pythons.
The Agta tend to be not quite so excited; Greene and Headland found that
one in four Agta men had been attacked by a reticulated python.
Of the 120 men whose stories were considered for the study, six had
been killed by a python. That’s a death-by-python rate of 1 in 20. Those
are lousy odds, but most of us have escaped such risks by living in
houses and cities and living where our ancestors killed off the most
dangerous predators, be they tigers, cave bears, or giant, carnivorous
kangaroos. We should be grateful for having escaped—and yet we haven’t
really escaped, because our bodies are burdened by our long history of
trying to get away.
When our hamburger-size ancestors lived in trees, it was
extraordinarily valuable to be able to respond immediately to the
potential presence of a predator. Many primate species have alarm calls
that are specific for different predators. The first primate nouns
were almost certainly those embedded in calls that meant, “Oh shit, big
cat!” “Oh shit, giant eagle!” or “For the love of god, did you see the
size of that snake?” In this way, predators may have had a positive
impact on who we are now, having given us the precursors of language, or
at the very least, cussing.
In addition to inventing words for these predators, we also responded
in other ways. When we saw or heard a sign of danger—a movement in the
grass, a strange shadow—hormonal reactions screamed out inside our
bodies. These fight-or-flight responses sped up the heart, increased
blood flow to muscles, caused hyperventilation (to get more oxygen for
quick reaction), and made us more likely to respond quickly to a
predator by searching for it, hiding, running away, or for the truly
brave, throwing a stick and then running away.
These fight-or-flight signals and associated jumpiness and anxiety
are part of the problem in modern urban life, part of our discontent.
They are triggered by all sorts of ordinary activities. Thinking of
taxes causes our hearts to beat fast. So does being late for a meeting,
forgetting your homework, or contemplating how to pay for a home
improvement. In none of these cases does our fight-or-flight response
serve a purpose. It gets us agitated. It makes our heart beat faster. It
prepares us to run, but to where? To what end?
Right now there are anxious people all around you, ready to run from
predators that aren’t there. Our misplaced anxiety can seem silly (the
other day I just about melted down while trying to find my keys so that I
could drive to the gym, where I was planning to run in place). But it
is still a serious problem that can cost money and can cost lives. We
have resolved this plague in part by medicating. Xanax, Valium. and
other drugs help. “There are no more leopards,” the little pills say,
and we rest more easily.
Anxiety is just one lingering result of predators’ influence. Another
is, well, tingly. When you are spooked by a sound or a testy boss, the
hair on your arms stands up. Along with the upright hair come chills.
But why does this happen? Once upon a time, when we still had fur, when
our hair stood on end it made us look bigger, less like a Big Mac and
more like, well, something slightly larger than a Big Mac. But now that
we have lost most of our hair, the chills that run through our body and
the contraction of the tiny muscles in our skin that pull our hair
erect simply make us look ridiculous, more cowardly than bold.
Many traits that influenced our ability to spot predators or flee
from them have been under strong natural selection for much of the past
40 million years of primate evolution and even before then. (We have
been prey essentially since the beginning.) Researchers are just
beginning to explore these possibilities. Lynne Isbell at the University
of California-Davis has argued that the range of our color vision evolved
in part because those of our ancestors who could see more colors were
more likely to spot snakes. A study this year found that children spot snakes more quickly than they do flowers
. They also spot snakes when using color vision more quickly than in
gray scale. Our interactions with other species (be they snakes, or as
some have argued, fruits) shaped our eyesight. Our screams, those
preverbal (and universal) utterances, are alarm calls signaling,
simultaneously, both a threat and the need for help.
But it wasn’t just predators that influenced our evolution. Parasites
and pathogens have also shaped our bodies in ways that are affecting
you now. With predators, most of our adaptations relate to avoiding
encounters in the first place, for the simple reason that by the time we
encounter a predator, it tends to be too late. But once we are attacked
by parasites, we often still stand a chance. Among the deadliest
parasites in human history are those carried body-to-body by mosquitoes,
such as the malaria parasite. Those ancestors who lived in areas where
malaria was and is most problematic evolved responses to escape Plasmodium’s
deadly wrath. One adaptation puts people at an increased risk of
sickle-cell anemia, and another raises the risk of favism, a condition
in which consuming fava beans causes anemia. Even the relative
prevalence of different blood types has been argued to be a consequence
of Plasmodium’s influence; some blood types appear to be more resistant to malaria than others.
Lice and other parasites and the diseases they carry may have played a
role in our loss of hair; parasites now have fewer places to hide.
Parasites might have played a role in our original sociality, too,
having brought us together to pick lice off one another’s backs (and
feel the endorphin release and social appeasement
that rewards such behavior). Then there are the parasitic worms whose
presence may have shaped our immune systems to such an extent that some
of us miss their absence; autoimmune disorders—including Crohn’s disease
and asthma—have been linked to now-obsolete adaptations to keep these
worms in check.
How our bodies work (or fail to work) in modern environments relates
not to the species we confront now, but the collective effect of the
species we confronted over millions of years. We are left with the
bodies that were best able to survive despite the daily threat of being
eaten by a predator, sickened by a parasite or pathogen, or otherwise
assaulted by Mother Nature’s well-armed hordes. Of course, we are still
evolving. In every generation, some genes are favored relative to
others, and yet the rate of our evolution is slow relative to how much
we have changed. And so we go on getting anxious when our football team
loses and letting our hair stand on end, ridiculously, when we are
scared. We could bemoan these legacies, but it makes more sense to
confront them head on, to consider just how we should live not in light
of the bodies we wish we had but instead with the ones we are born with,
bodies that evolved in the wild, thanks to ancestors who only just
barely got away.
