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Imagine a child skipping down the sidewalk: swinging their
arms as they bound along. Kids skip a lot and make it look
practically effortless. But as we age, most of us stop
skipping. It takes a lot of energy, and it’s just not a practical way to get around.
But across the animal kingdom, there are other animals
that skip and not just when they’re young and developing.
They show us that skipping isn’t always impractical.
Sometimes, this whimsical movement is a pretty decent
way to get around. Animals have all sorts
of ways of getting from A to B. We humans are a little unusual
in that we walk on two legs, so we move differently from many
species. But like us, many animals can move
around on just two legs, and a lot of them can also walk, run, hop, and jump.
For some animals, though, these options don’t offer an
efficient enough way to move as fast as they need to. And
that’s why some of them turn to skipping. Just like running, skipping is a faster
way of getting around than walking. But for us,
it takes about 24% more energy than running at the same pace,
so it doesn’t make a whole lot of sense.
But for certain primates, who aren’t as specially adapted to
walking on two legs, skipping can actually be pretty
practical. Now, when I
say “skipping,” you’re likely picturing the motion of a young child bounding along with
a spring in their step.
This movement is technically known as bilateral skipping
because the lead leg alternates with each stride. So you
push off with one foot in front, then the other, and so on.
We may be the only animals that skip exactly like this! But
there’s also unilateral skipping, where the same foot
stays in front the whole time. And this is the kind of skipping
we tend to see in other animals.
For instance, over in Madagascar, our relative the lemur
will often get up on two legs and skip across the ground
any time it needs to cover some distance quickly. The reason these primates
skip much more readily than adult humans probably comes down to skeletal
differences. Since lemurs evolved
to walk and climb with four legs, when they do get up on two legs,
their hind limbs don’t straighten and stiffen the way human legs do.
With their knees and hips always slightly bent, they can’t
produce the same amount of force when they run as we do
by fully straightening our legs. So, skipping can be a better
way to move fast. Plus, unilateral
skipping is actually more stable than running at the same speed because
the body spends less time supported by just
one leg. And for an animal that’s not well adapted to moving on two legs,
stability is likely important.
So, it’s no wonder lemurs seem to prefer skipping to
running. But there are skippers
in other parts of the animal kingdom too, like birds.
Birds’ center of gravity is dramatically different from ours,
and their legs and hips are positioned in a way that makes
bouncing movements easier than running. Little songbirds are light enough
that they can just hop around easily enough,
but larger birds like crows and magpies often skip when they need
to get across the ground quickly.
It might not be more efficient than running, but it’s a more
stable way of getting around, for about the same cost.
Out in the deserts of North Africa and Asia, there’s another
skipping animal known as the jerboa. This two-legged
rodent mostly gets around by hopping. But when evading
predators, it mixes things up by running, skipping, and
changing direction. Since it lives out in
the open sand where it’s hard to hide from predators, these erratic movements
may help jerboas avoid getting caught.
Unlike for us humans, skipping just makes sense for all of
these animals because they’re built differently. We’re just not made for skipping here
on Earth. But there’s at least one place where
skipping might be practical for humans and that’s on the Moon!
When Apollo astronauts walked on the Moon, their stride
often naturally turned into a skip. It’s easier to skip in low gravity,
and NASA scientists hypothesized that
astronauts may have preferred this type of movement because of the stability it offered.
Here on Earth, scientists have simulated low gravity
conditions by putting participants on treadmills while they
were partially lifted by harnesses. Analysis of their
movements suggests it was easier for them to skip than to
run. The sample size of this
study was small, as is the number of astronauts who have walked
on the Moon, but computer models have backed up the idea
that skipping on the Moon may be practical.
On the lunar surface, you can skip for about the same
amount of energy as it takes to walk on Earth, and you’ll be
more stable. For most of us non-astronauts,
skipping will still never be practical, unless you’re
looking for a good workout. Skipping burns more energy and
is thought to be easier on the knees than running.
So if you ever feel inspired to embrace your inner child, or
your inner lemur or jerboa, go for it. You’re never too old to
go for a skip! But don’t skip the
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