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  • Hey, Vsauce. Michael here. Ten

  • centimeters - about four inches. This

  • is how much taller on average people

  • are today than they were 150

  • years ago. Better nutrition and medical care

  • early in life has allowed us to better take advantage of the blueprints

  • within our genes. Blueprints that carry plans for just how

  • big a healthy human being can get given

  • an optimal environment. In terms of height, those plans

  • rarely exceed 7 feet 6 inches.

  • But individuals with endocrine disorders, for instance a tumour,

  • near the pituitary gland in the brain can experience growth that occurs more

  • rapidly and for a longer period of time

  • than usual. For instance, Igor Vovkovinskiy,

  • who at 7 foot 8 inches is the tallest man currently living

  • in America. The tallest living person anywhere on Earth

  • is Sultansen, who at 8 foot 3 inches tall

  • also holds the Guinness world record for largest hands

  • and feet. But the tallest person

  • ever officially recorded was Robert Wadlow.

  • He was the size of an average adult male when he entered

  • kindergarten at the age of 5. When he died

  • in 1940 at the age of 22, he was

  • 8 foot 11 inches tall. Andre the Giant

  • was 7' 4". And this

  • is me holding a 12-ounce can.

  • Here's Andre doing the same. Human size variation

  • is fascinating, but what's the maximum, biologically

  • how big can a human get? And more importantly,

  • how big are you really?

  • It turns out that today, now

  • in history, average human height

  • is probably quite near the genetic

  • limit. By manipulating the very genes responsible for height,

  • we may be able to add an extra 15 centimeters or so to that

  • average, but beyond that we are likely to hit

  • a ceiling. In order to regularly produce

  • people over 8 feet tall, 2.44 meters,

  • those people would probably need to be

  • a different shape. Not human shaped.

  • This is because of the square-cube law.

  • As a shape grows, say, taller, its volume increases at a greater rate.

  • Take a look at this cube. If we make it 10 times larger,

  • well, sure, it's 10 times as tall, but the area covered by its faces

  • is 100 times larger and its volume,

  • the space within it, is 1000 times larger.

  • Now, since weight is connected to volume, this cube

  • only has one hundred times the cross-sectional area to support itself,

  • but one thousand times the weight to support.

  • So, if you were ten times larger,

  • and still shaped like a person, that is your proportions were the same as they

  • are now,

  • you would need to either have a skeleton made out of something stronger than bone

  • or bones that were monstrously thick, like way out of proportion.

  • But even if you solved the bone and muscle strength problem,

  • there would still be a whole host of other issues. For instance, your heart

  • wouldn't scale up fast enough to keep blood pumping throughout a body

  • that large. Animals can get that big,

  • because their proportions and organs are quite different.

  • Chris Howard from Earth Unplugged tipped me off to the

  • giant, not human proportioned, legs

  • of the largest land animal ever known to have existed with

  • the certainty of a complete skeleton,

  • the awesomely named giraffatitan.

  • Discovered in Tanzania and now mounted in Berlin's Humboldt museum

  • it probably weighed 20 to 30 thousand kilograms.

  • The Bruhathkayosaurus may have been even larger,

  • but this is controversial because we only have a few of its bones.

  • Estimates put this guy at 140,000

  • kilograms. Any larger than that,

  • and in order to survive long enough to reproduce,

  • an animal would need more buoyancy to counteract its weight

  • than air can provide. This is one of the reasons

  • blue whales love the water so much.

  • The heaviest blue whale ever measured by NMML

  • weighed in at 177,000 kilograms,

  • making it the heaviest animal we are aware of

  • that has ever existed. It might be the heaviest

  • possible, because animal size is limited by simple geometry

  • and the gravity of our planet.

  • Theoretically, humans born on Mars could grow a few inches taller,

  • because gravity there is only one third of what it is on earth.

  • The trade off of course being that their bones and muscles wouldn't grow strong

  • enough

  • for them to ever visit Earth and

  • enjoy it. The point is, in order to have the same shape and proportions that we

  • have now,

  • we can't really get that much bigger.

  • Some of the higher estimates of the upper limit up

  • average human height are around 7 feet tall.

  • A person who is more than 9 feet tall would struggle to move around.

  • aAd up in the 12- to 15-foot range, it would be

  • difficult to live very long at all.

  • But what does size mean?

  • Where do you really begin

  • and end? So far we have been measuring people using

  • their rigid boundaries. It's a good one to use,

  • it's very common, but of course, when I speak

  • I can fill an entire room and when I shout

  • I can fill city blocks. That's

  • huge. Of course, my voice is not a part of my physical body.

  • It's not part of the matter that fits within my skin container.

  • But it's relevant to the question of how big

  • a person is. How large of an

  • impact on their environment can a person have using what comes directly

  • from their bodies? Well, Guy Murchie illustrated this quite well

  • in his tome "The Seven Mysteries of Life."

  • The little solid dogs are small,

  • but their sound and smell extend into shapes and sizes no creature could even

  • dream

  • of filling up with their bodies on earth.

  • Let's begin with sound. How far

  • can your loudest shout travel? How much bigger are you?

  • The volume of space within which people are aware that you exist

  • when you shout. Well, the loudest shout a human can make is about

  • 88 decibels from 30 centimeters away.

  • A shout like that will die out down below the threshold of human hearing

  • in our atmosphere, after traveling about 5

  • kilometres or 3 miles. A person standing downwind from you

  • might be able to make you out a little further than that,

  • but the point is, in space no one

  • can hear you scream. And on earth, from 5 kilometres away,

  • no one can hear you scream.

  • But could they see you scream? Really, could they see you

  • at all? Well, on the surface of the earth,

  • the furthest you can see another person is

  • the horizon. If you and another person are standing on the ground,

  • that distance is about 5 kilometers

  • or 3 miles. Any further away than that and you will literally be hiding

  • behind the curvature of the earth. So what about

  • in, say, outer space, where moving away from another person doesn't mean

  • eventually hiding behind the earth. Well, as an object moves farther and farther away,

  • it becomes smaller and smaller. Of course, the

  • actual size of the object doesn't change. What does change to you

  • is its angular size. This brilliant measurement describes how much

  • space in your visual field an object takes up.

  • Imagine your visual field as a complete

  • circle, 180 degrees of which go from the horizon in front of you

  • to the horizon behind you. So, an object with an angular size

  • of 90 degrees would have to be big enough

  • and close enough, so as to take up all the space from the horizon

  • to right above you. Interestingly, your

  • thumb held at an arm's length away from your face

  • takes up about one degree of your visual field. Its size

  • is 1 degree. The Moon takes up about

  • half a degree at all times. It sometimes appears

  • larger at the horizon, but that's because of an illusion that AsapSCIENCE

  • covered

  • really well. Te smallest angular size we can see with the naked eye

  • is about one arc minute, a sixtieth

  • of a degree. But given enough contrast, we can see things like Sunspots,

  • a mere 20 arc seconds across,

  • a third of a sixtieth of a degree. Plugging in numbers to do the math

  • will tell us that with perfect conditions:

  • outer space, no air, no obstructions, a lot of contrast, because you are wearing

  • bright white, the farthest away

  • a person could see you with their naked eye would be about

  • 10 to 15 kilometres.

  • Any further away than that and they will have passed the edge

  • of your naked eye visibility existence.

  • But... do you smell that? It might be

  • you. If we consider the senses of other animals,

  • your smell, your scent, might be your

  • largest earthly dimension.

  • You know how animals like cats and dogs have those cute little

  • wet noses? It's called

  • a rhinarium. Rhinariums allow mammals to smell

  • really really well. They don't just pick up molecules that float by,

  • they localize them. Air cools the wet nose,

  • allowing the animal to tell the source of the smell.

  • It's the same as when you wet your finger and stick it in the air to tell