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BY GEMMA TARLACHFeet
THINGS
YOU
DIDN’T
KNOW
ABOUT...74 DISCOVERMAGAZINE.COM
humans and mice), digitigrade (only toes on ground,
like cats and dogs) and unguligrade (hooved toes on
ground, like horses and giraffes). 12 We’re still sorting
out how our own feet work — and sometimes don’t.
Stress fractures in the lower legs, a common running
injury, are typically blamed on pounding the pavement.
A study published in PLOS One in January, however,
suggested the real culprit is not the force of a run-
ner’s foot hitting the ground. 13 Instead, it’s the strain
that contracting muscles put on the lower leg bone
as they pull away from it later in the stride. Though
preliminary, the team believes the results may lead
to better monitoring and training for athletes at risk.
14 Many insects, spiders, lizards and amphibians pull
off athletic, even acrobatic moves by climbing vertical
and inverted surfaces, thanks to a variety of adapta-
tions to their feet. 15 The bottoms of gecko toes, for
example, are covered with super-flexible, microscopic
hairs that grow at oblique, or non-perpendicular,
angles. The hairs’ teensy scale creates electromagnetic
attraction to the wall or ceiling surface, but their
angle and flexibility allow the gecko to easily unstick
its feet as it moves. 16 Other gravity-defying animals,
including many invertebrates, have wet feet, which
scientists thought helped them adhere to flat surfaces.
But a study of stick insects found that secreting liquid
from foot pads has nothing to do with, well, sticking.
17 Instead, the liquid seems to act as a lubricant that
helps the insects unstick their feet as they move across a
surface. The findings could prove significant in robotics
design. 18 Whether robotic or nature-made, feet will
continue to evolve. Except for the International Foot.
On July 1, 1959, for the first time, the U.S. and several
other countries standardized the yard (0.9144 meters, if
you’re curious). 19 Because there are 3 feet in a yard, the
formal decree filtered down to the smaller unit of mea-
surement, and the International Foot became exactly
0.3048 meters. As a result, a foot got slightly longer in
the U.K. and slightly shorter here. 20 Our pre-1959
foot, 0.3048006096 meters in length and now known
as a U.S. survey foot, still shows up on some older maps
and other geospatial systems — but not Apollo 11’s
guidance computer, which was calculated in metric.^ DGemma Tarlach is senior editor at Discover.1 When Apollo 11 touched down on the moon, could
Neil Armstrong have made a “giant leap” if we’d
never evolved feet? “One small slither for man” just
doesn’t have the same ring to it. In truth, our feet
have enabled one of our most impressive, ah, feats.
2 With its big heel bone, short toes and long, stiff arch,
the human foot is a defining trait of our genus because
it enabled efficient bipedalism: locomotion on two legs.
3 Being bipedal made humans great long-distance
walkers and runners while freeing our upper limbs
to make and use tools, including weapons. You could
say it was a giant leap on the way to becoming Earth’s
dominant animals, for better or worse. 4 Already fully
bipedal ancestors such as Homo erectus walked out
of Africa and across the Old World, reaching East
Asia by at least 1.6 million years ago, but researchers
still aren’t sure how far back our fancy feet evolved.
5 Australopith Lucy, a 3.2 million-year-old potential
predecessor, appeared to be fully bipedal. However, in
2018, paleoanthropologists found that a juvenile fossil
foot from the same species was much closer to that of
climbing apes. 6 Of course, feet go much further back
in evolution. Diverse and unrelated organisms share
remarkably similar genetic pathways of development
for their species-specific limbs. 7 The near-universal
distribution of these gene clusters among animals,
from wombats to wasps, humans to halibut, suggests
they arose in a common ancestor
more than 500 million years ago.
8 But the very first “foot” may
have belonged to a mollusk.
They’ve been around for about
540 million years, and many
species have muscular under-
sides, also called feet, that allow
them to move via contractions. 9 The tentacles
of squids and arms of octopuses, both mollusks,
evolved from these muscular “feet.” 10 Among
terrestrial vertebrates, feet are far more uniform.
We all inherited the same basic suite of foot bones
from the first four-limbed vertebrates, or tetrapods, to
leave the seas for dry land more than 350 million years
ago. 11 The shape and position of those bones diversi-
fied, sometimes dramatically, as different foot postures
evolved, such as plantigrade (entire foot on ground, likeDISCOVER (ISSN 0274-7529, USPS# 555-190) is published monthly, except for combined issues in January/February and July/August. Vol. 40, no. 5. Published by Kalmbach Media Co., 21027 Crossroads Circle, P.O. Box
1612, Waukesha, WI 53187-1612. Periodical postage paid at Waukesha, WI, and at additional mailing offices. POSTMASTER: Send address changes to DISCOVER, P.O. Box 8520, Big Sandy, TX 75755. Canada Publication
Agreement # 40010760. Back issues available. All rights reserved. Nothing herein contained may be reproduced without written permission of Kalmbach Media Co., 21027 Crossroads Circle, P.O. Box 1612, Waukesha, WI
53187-1612. Printed in the U.S.A. SHUTTERSTOCKPHOTOSFROMTOP:^SUTTHABURAWONK;^ Z.^ A
YSE^ KIYAS^ ASLANTURK;^ KETPACHARA^ YOOSUK;^KUTTELVASEROVASTUCHELOVA;^ RANGIZZZ;^ ERICISSELEE;^YELLOWCAT;^TANKIST276Remarkably
similar genetic
pathways guided
the development
of all these diverse,
species-specific feet,
except for one: The
tentacles of octopuses
evolved from the
muscular underside of
an ancestral mollusk.
Our foot’s large
heel bone,
stiff arch and
short toes allow
efficient upright
walking.