perhaps, but always present. And so too is the met-
abolic mess it makes of us, a permanent state of fight
or flight that we have come to define by the simple
label “stress.”
It’s a good word, actually, one with a lot of ap-
plications. Buildings undergo stress; machines
undergo stress; fault lines in the Earth’s crust un-
dergo stress. And all of them, at some point, can
crack or collapse. The same is true of us.
In the U.S., 75% of adults report that they have
experienced at least one stress symptom in the
past month, and 35% of people report experienc-
ing chronic work stress, according to the American
Psychological Association. The National Institutes of
Health estimates that at least 1 in 21 Americans reach
that crack-and-collapse threshold in their lives,
crossing over into full-blown panic attacks. The
emotional beating that stress administers is matched
by the physical. A constant state of high alert can
contribute to serious health problems and disease:
Type 2 diabetes, as the liver continually boosts sugar
levels to give you the energy you need for the antici-
pated battle; high blood pressure and cardiovascular
disease, as the heart and circulatory system spend
too much time in overdrive; obesity, as the high lev-
els of cortisol make you crave sugary, fatty foods; vi-
ruses and infectious diseases, as energy that would
normally go to sustaining the immune system is di-
verted elsewhere. Fertility and libido plunge too.
Who has time to think about breeding when you feel
as if you’re in a fight for your life? Insomnia, depres-
sion, headaches and even heartburn from all those
never properly digested meals can combine to make
a high-stress life an ongoing misery.
As the stress epidemic has grown over the gen-
erations, experts have done what they could to un-
derstand it and treat it. Hans Selye, a 20th-century
Vienna-born endocrinologist, is seen as the archi-
tect of our modern understanding of stress, fram-
ing it as an adaptive response, but one that quickly
moves from what he labeled the “alarm stage”
(fight or flight), to the “resistance stage” (in which
the body adapts to the ongoing stressor), to the
“ exhaustion stage,” in which the body is drained of
all resources to manage the stressor and we simply
break down.
Selye posited that the body’s ideal state of equi-
librium is maintained by balancing stress along
two different axes. One is the eustress (or good
stress) versus distress (or bad stress) axis—thedle at least some of the dangers. When the lions
leaped from behind a bush, our bodies responded,
kick-starting a metabolic cascade that tensed our
muscles, quickened our breathing, accelerated our
hearts, shut down digestion (no use wasting calo-
ries processing your last meal when you might be
about to become a predator’s next one) and gener-
ally girded the system to fight. When the danger
passed—if it passed—you returned to baseline.
As for spending a lot of energy fretting about
the next time the same kind of peril might present
itself? We didn’t bother. The real needs of the mo-
ment trumped the prospective perils of the future.
And with a brain that was less than half the size
of modern human brains—not yet equipped with
sophisticated problem-solving or planning skills—
we wouldn’t have been able to ruminate about the
future even if we were inclined to try.
Things changed. We got smarter, more complex,
much more creative; we left the raw danger of the
savanna for the safer embrace of villages and towns
and cities and nations. By now, ages later, we eat bet-
ter, we live longer, we have many healthy children
who grow up to have still more.
That doesn’t mean that we face no dangers.
They’re just different, more subtle ones. And our
big brains mean we’re now constantly aware of
them—able to dread them and plan for them and
brood about them. Your Homo habilis ancestors did
not have a mortgage, but you do. Homo habilis did
not have a boss either—or deadlines to meet or mar-
ital woes or home repairs. And Homo habilis didn’t
spend time worrying about health concerns—like
those headaches you’ve been getting, which might
be nothing at all but could be something terrible
and either way you have to live with the uncertainty
because your doctor couldn’t schedule you for an
MRI until next month—an MRI that you just know
is going to cost thousands of dollars and that your
insurance won’t cover because, well, it never does.
We don’t have a lot in common with Homo habilis
when it comes to threats except for this: our bodies
react to them more or less the same way. That bio-
logical cascade—the hormones that send the body to
battle stations with all of the metabolic urgency and
tension that implies—has barely changed. Only, un-
like Homo habilis, we almost never get the all clear.
The lions that stalked our ancestors at least took a
break. But the cycle of stressors modern humans
face are ongoing—worse some days than others,