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Hey smart people, Joe here.
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I am a descendent of giants.
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With a grandfather, dad, two uncles, and an aunt all towering over 6 feet tall. Siblings and cousins, too.
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We are the people you don't want to stand behind at a Bon Jovi concert, but we're also the people who can get that thing off the top shelf for you.
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At 6'3", I turned out to be the short one in the family.
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Now that I have a son myself, I'm wondering if he's going to be tall too.
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Is height only written in our genes, or is there something else that determines how tall we get?
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These days, the average American woman is about 5'4", while the average Joe American male is about 5'9".
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But… human height has had its ups and downs over the centuries.
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Three million years ago, our ancestor Australopithecus only stood about 4' tall.
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One-and-a-half million years later , Homo erectus, the first early human to use complex tools, reached up to 5'7".
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And by the Stone Age, men of the Gravettian hunter-gatherer culture in Europe stood at an average of 6 feet.
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Most of the historical data we have is for male height, because . . . reasons.
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Then agriculture happened.
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When Europeans switched to a lower-protein, higher-grain diet, men gradually lost 8 inches in height, on average.
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And they stayed that way for thousands of years.
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By the time the 18th century rolled around, the average European man was only 5'5" inches tall.
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But when those Europeans emigrated to America, their kids grew up to be 5'8" inches tall on average.
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A huge jump in just a generation.
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During the Industrial Revolution heights took a dip due to urban crowding and disease, but soon after, the human height boom continued and continues today.
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Every decade for the past couple centuries Europeans have grown an average of about half an inch.
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Today, Dutch men are the tallest people in the world, with an average height of just over 6 feet—back to where those Gravettians started 8 millennia ago—and, almost as tall as me.
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These fluctuations of height, sometimes within a single generation, show that our environment determines a big part of how tall we are.
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But people in different regions, and different families, show us that height has genetic causes too.
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So which has a bigger role, nature?
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Or nurture?
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In the early 19th century, scientists first noticed a correlation between people's heights and their wealth — people from poor backgrounds tended to be shorter than people who were more well-off.
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Instead of asking whether someone's upbringing might influence their height, many scholars at the time decided tallness was a physical mark of "superior" humans.
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Francis Galton — who would later become infamous for popularizing eugenics—was the first scientist to conduct a large-scale, systematic study of height.
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He precisely measured the height of thousands of people as part of a sort of scientific side show.
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But Galton's results were confusing.
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Parents' heights often didn't predict the heights of their kids.
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The heights of siblings on the other hand, were much closer.
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This inspired scientists to look at height in twins.
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Studying twins can teach us a ton about how genes and environments influence human attributes.
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Fraternal twins can be as different genetically as any other pair of siblings, with the added advantage of being exactly the same age.
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Identical twins are genetically, well, identical.
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So we can see how much genetic carbon copies end up differing.
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And twins separated at birth offer a window into what happens when genetically identical individuals grow up in very different environments.
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Turns out that twins, especially identical twins, tend to be close in height—but not exactly the same.
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Twin studies, like history, show us genes can only be part of the story when it comes to height.
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So, how big a part?
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In 2007, scientists compared height and DNA between more than 11,000 pairs of siblings and found that, across humans, 86% of height variation can be explained by genetics.
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As traits go, this is very high; for comparison, genetics only explains about 26% of left-handedness.
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So we should be able to predict a person's height from his or her DNA right?
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Well, not so fast.
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We know genes make a huge difference, just not which genes.
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So far, scientists have identified about 800 genes that influence height, but many of them only make a tiny contribution.
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Take HMGA2, one of the first genes linked to height.
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Having one copy of the “tall” version only “lifts” a person about an eighth of an inch, so even if you inherit a copy from both of your parents, that still only gains you a quarter of an inch at most.
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Altogether, the 800 height genes we know of can only explain 27% of how height varies between people.
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There's clearly lots of genetic influence we don't understand.
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Maybe the effects of some genes add up in unexpected ways — genes may interact in combinations, where four and four makes sixteen, not eight.
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If we could just study the DNA of all the 7 billion people on Earth, maybe we would find all the genes that affect height.
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Or maybe we'd find that scientists have overestimated the contribution of genetics.
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Because our environment, defined by health and diet, certainly has a hand in shaping our height.
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South Koreans today are more than an inch taller than North Koreans, despite minimal genetic differences.
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Clearly, one's diet during childhood, is crucial in determining adult height.
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That's why humans shrank with the switch to agriculture and again during the Industrial Revolution.
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Today, most scientists agree that nature and nurture combine to shape our height.
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Some even propose calling height an “omnigenic” trait — one that nearly all our genes influence in some way.
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For now, the only surefire way to know how tall you'll end up… is just to wait and see.
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Stay curious!
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Hey guys, I want to take a second to tell you about "REINVENTORS". It's a new show from PBS Digital Studios and KCTS 9 in Seattle.
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We'll introduce you to the scientists and tinkerers in the specific North West make cutting edge of green technology.
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They'll try edible plastic, so you don't have to. And bring you to unexpected places like a garage in Seattle with a nuclear reactor in it.
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You can check out REINVENTORS and subscribe to them at the link in the description.