this guy made history in 2012 for being
the first amputee runner to compete in
the Olympic Games its Oscar Pistorius
who you might also know for murdering
his girlfriend but this is a video about
feet so let's set that aside Pistorius
had to fight for his right to compete in
the Olympics by proving to officials
that his blade-like prosthetic feet
didn't give him an extra advantage over
athletes running on regular old flesh
feet there are other blade runners
fighting the same fight behind him the
German long jumper Marcos rim was barred
from competing in the Rio Olympics the
college track athlete hunter Woodhall
had to make the case to the NCAA and
Paralympian Blake Leeper is gearing up
for the same fight to compete in the
2020 Olympics and it all makes you
wonder why does the foot designed in a
lab look so different from the
biological human foot it might be
because the human foot is kind of a
design disaster podiatry is a five
billion dollar industry a majority of
Americans will experience significant
foot pain at some point in their lives
and as many as 10 percent of us will
experience inflammation in the band of
tissue along our arches otherwise known
as plantar fasciitis why though weren't
humans evolved to walk long distances
and isn't walking upright on two legs
the trait that first separated us from
other primates so why hasn't natural
selection selected a cooler better less
injury-prone foot for us some theories
posit that we're so plagued by foot
problems because we evolved to walk
barefoot out of nature over soft sweet
earth but now we've thrown off the
delicate biomechanical balance of our
feet by wearing big mushy cushiony
tennis shoes meanwhile our bones take a
beating from walking and standing on
super hard surfaces like concrete but
other researchers say it goes back way
further than that jeremy de silva is an
anthropologist who studies human
evolution and argues that foot problems
exist way back in the fossil record
fossils show evidence of osteoarthritis
and compression fractures and flat
arches which means foot pain millions of
years ago
DeSilva makes a convincing case that the
real source of our foot problems is the
janky design as I mentioned earlier what
we're looking at are our paper clips and
duct tape our primate ancestors spent
most of their time in trees our feet
then were originally meant for climbing
and grasping but four million years ago
and possibly earlier some Apes started
dabbling in bipedalism experts haven't
agreed on why hominins developed this
trait perhaps it was a more efficient
way to travel while scavenging for food
or maybe it was to enable persistence
hunting tracking prey over such long
distances that they became overheated
and simply laid down from exhaustion
no weapons required whatever the reason
bipedalism is the defining trait of
humans going bipedal involved some
painful and atomic ultradox including
everything from where the spine attaches
to the skull to the angle of the femurs
and of course the shape of our feet
let's talk mechanics a foot is a
propulsive lever it needs to be stiff
enough that we can push off the ground
and propel ourselves forward but it
needs to be elastic enough to store the
mechanical energy that's generated each
time the foot strikes the ground
that's how designers ended up with this
blade shaped for athletes the human foot
on the other hand has 26 bones 33 joints
and over a hundred muscles tendons and
ligaments that's because it was built
for grasping all those joints let it
flex so it's not inherently rigid enough
to give us the propulsive power we need
here's what had to change back when we
were climbers our big toe used to be
opposable like our thumbs but to help
make the foot more rigid it became
shorter stiffer and in line with our
other toes and we developed arches to
absorb the force of impact each time our
foot hits the ground
our ligaments got thicker to help hold
all these small bones firmly in place
bipedal locomotion is a notoriously
complex mechanical engineering puzzle
that scientists have been working on for
decades
and in the case of human feet you could
say natural selection is still in the
early design phase DeSilva uses the
ostrich as an example of a foot from the
natural world that resembles the
prosthetic blades that were perfectly
designed for running on two feet but he
also points out birds have a big
bipedalism head start just look at their
ancestors
they've been bipedal for 230 million
years while we've only been bipedal for
about five million and a big take away
from his talk natural selection isn't
selecting from an endless menu of
options rather it's a constant series of
small modifications to the original
design so in our case it slowly modified
flexible grasping hands into more rigid
propulsive levers which left us kind of
vulnerable to some aches and pains but
considering our feet are modified a pans
they do a pretty good job and
considering where the most successful
primate neh mammal neh species on the
planet it's a pretty decent compromise
thanks for watching if you're super
interested in the scars of human
evolution you can see the whole talk on
Boston University's YouTube page if you
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thanks again we'll see you next time