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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 Sultan KĂ¶sen, 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,

• 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