Today, a billion heartbeats. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
Stephen Jay Gould asks us to
muse upon the allotted lifetimes of mammals.
Gerbils live only a few years, most dogs get beyond
twelve, elephants and the big whales live about as
long as we do. Now, says Gould, if our reaction is
pity for those short-lived species, let's ask just
how we should measure the length of a
The clock on the wall is misleading. In another episode, I talk about the
way smaller creatures have to perceive the passage
of time much differently than we do. A small
creature, watching you and me, has to see us as
though we're moving through molasses
Think about heartbeats and respiration, says Gould.
Your heart or mine might beat seventy-two times per
minute, while we breathe eighteen times per minute.
The next time you hold your cat, take note of its
pulse and breath. Both are much more rapid than
yours. A waking cat lives on a faster track than we
It turns out that any mammal's heart beats about
four times per breath. However, pulse and
respiration each decrease roughly as the fourth
root of body mass. That means a twenty-five-pound
whippet breathes twice as fast as a
So let us look upon that clock on the wall, not as
measuring minutes, but rather heartbeats of the
creature watching it. It turns out that all animals
live for roughly a billion heartbeats. With a
heartbeat clock, our lifetimes would all be roughly
the same. Well, not exactly ... we humans are
statistical outliers. We mature far more slowly
than other creatures and our hearts typically beat
around three billion times. However,
that's still the same order-of-magnitude as the
rest of the animal kingdom.
Gauging life in heartbeats or breaths reveals, once
more, how deeply subjective
time is. The second law of thermodynamics tells
us that we experience time moving only from past to
future. That's because the world we perceive is
statistically irreversible. And the rate at which
we see time moving in only one direction, is
dictated by our hearts and lungs.
I watch the clock on my wall -- its second hand
ticking at a rate very close to my own heartbeat --
and I better understand the old song about a
Ninety years without slumbering
Tick, Tock, Tick,
His life seconds numbering
Tick, Tock, Tick,
And it stopped short -- never to go again
When the old man died.
It is quite wondrous to view all animals as one
universal creature scaled up
or down. The sizes of brains increases roughly
as the three-quarters power of body mass. The
cross-sectional area of a leg increases as the mass. We may
be statistical outliers, we humans. But
it's a lot harder to put on airs when we can see
ourselves as scaled-up cats, or scaled down
elephants. And, at the same time, I also read in
that a fine dimension of hope.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
S. J. Gould, The Panda's Thumb: More Reflections
in Natural History. New York: W. W. Norton &
Company, Inc. 1980. Gould deals with many of these
issues here, but see especially, Chapter 8.
For more on these issues, see Engines episodes
1407, 1498, 1560, and 1564.
The Engines of Our Ingenuity is
Copyright © 1988-2003 by John H.