Hey smart（聪明的） people, Joe here. I'm a descendant（子孙） of Giants, with a grandfather, dad, two uncles, and an aunt all towering over six feet tall. Siblings（兄弟） and cousins, too. 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（搁板） for you. At six foot three, I turned out to be the short one in the family.
Now（现在） that I have a son myself, I'm wondering（想知道） if he's going to be tall, too. Is height only written in our genes（[遗] 基因）, or is there something else that determines（决定） how tall we get? These days, the average American woman is about five foot four, while the average Joe American male is about five foot nine. But human height has had its ups and downs over the centuries. Three million years ago, our ancestor（祖宗） Australopithecus only stood about four feet tall. One and a half million years later, Homo（人） erectus（[拉丁语]直立的）, the first early human to use complex（复杂的） tools, reached up to five foot seven.
And by the Stone Age, men of the Gravedian hunter-gatherer（收集者） culture in Europe stood an average of six feet. Most of the historical（历史的） data（资料） we have is for male height because reasons. Then agriculture（农业） happened. When Europeans switched（开关） to a lower protein（蛋白质）, higher grain（谷物） diet, men gradually（逐渐地） lost eight inches（英寸） in height on average. And they stayed that way for thousands of years. By the time the 18th century rolled（滚动） around, the average European man was only five foot five inches tall.
But when those Europeans emigrated（永久(使)移居） to America, their kids grew up to be five foot eight inches tall on average. A huge jump in just a generation（一代）. During the Industrial（工业股票） Revolution（革命）, heights took a dip due（预期的） to urban（都市的） crowding and disease. But soon after, the human height boom（繁荣） continued and continues today. Every decade（十年） for the past couple centuries, Europeans have grown an average of about half an inch. Today, Dutchmen are the tallest people in the world, with an average height of just over six feet.
Back to where those Gravedians started eight millennia（千年期） ago. And almost as tall as me. These fluctuations（起伏） of height, sometimes within（在……之内） a single generation（一代）, show that our environment determines a big part of how tall we are. But people in different regions and different families show us that height has genetic（[-s]遗传学） causes too. So which has a bigger role? Nature or nurture（养育）?
In the early 19th century, scientists first noticed a correlation（相关） between people's heights and their wealth（ 财富）. People from poor backgrounds tended（趋向） to be shorter than people who were more well off. Instead of asking whether（ 是否） someone's upbringing（养育） might influence（影响） their height, many scholars（学者(尤指文学方面)） at the time decided tallness was a physical mark of superior（上级的） humans. Francis Galton, who would later become infamous（声名狼籍的） for popularizing eugenics, was the first scientist to conduct（指挥） a large-scale（刻度） systematic（系统的） study of height. He precisely（正好） measured（量） the height of thousands of people as part of a sort of scientific（科学(上)的） sideshow. But Galton's results were confusing.
Parents' heights often didn't predict the heights of their kids. The heights of siblings, on the other hand, were much closer. This inspired（激发） scientists to look at height in twins. Studying twins can teach us a ton（吨） about how genes（[遗] 基因） and environments influence（影响） human attributes. Fraternal twins can be as different genetically（基因地） as any other pair of siblings（兄弟）, with the added advantage of being exactly the same age. Identical（同一的） twins are genetically（基因地）, well, identical, so we can see how much genetic carbon（碳） copies end up differing（使…相异）.
And twins separated（使分离） at birth offer a window into what happens when genetically（基因地） identical（同一的） individuals grow up in very different environments. Turns out that twins, especially identical twins, tend to be close in height, but not exactly the same. Twin studies, like history, show us genes can only be part of the story when it comes to height. So how big a part? In 2007, scientists compared height and DNA between more than 11,000 pairs of siblings, and found that across humans, 86% of height's variation（变化） can be explained by genetics（[-s]遗传学）. As traits（特性） go, this is very high.
For comparison（比较）, genetics（[-s]遗传学） only explains about 26% of left-handedness（用右手或左手的习惯）. So we should be able to predict a person's height from his or her DNA, right? Well, not so fast. We know genes make a huge difference, just not which genes. So far, scientists have identified about 800 genes that influence height, but many of them only make a tiny（微小的） contribution（ 贡献）. Take HGMA2, one of the first genes linked to height.
Having one copy of the tall version（版本） only lifts a person about an eighth of an inch（英寸）, so even if you inherit（继承(传统等)） a copy from both your parents, that still only gains（获得） you a quarter of an inch（英寸） at most. Altogether（完全）, the 800 height genes（[遗] 基因） we know of can only explain 27% of how height varies（改变） between people. There's clearly lots of genetic influence we don't understand. Maybe the effects of some genes add up in unexpected（想不到的） ways. Genes may interact（互相影响） in combinations（结合） where 4 and 4 makes 16, not 8. 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.
Or maybe we'd find that scientists have overestimated（ 评价过高） the contribution（ 贡献） of genetics（[-s]遗传学）. Because our environment, defined（给…下定义） by health and diet, certainly has a hand in shaping（形成） our height. South Koreans today are more than an inch taller than North Koreans, despite（不管） minimal（最低的） genetic（[-s]遗传学） differences. Clearly one's diet during childhood（童年） is crucial（至关重要的） in determining（决定） adult height. That's why humans shrank（收缩） with a switch（开关） to agriculture（农业）, and again during the Industrial Revolution. Today, most scientists agree that nature and nurture combine（使结合） to shape（形成） our height.
Some even propose（提议） calling height an omnigenic trait（特性）, one that nearly all our genes influence in some way. For now, the only sure-fire way to know how tall you'll end up is just to wait and see. Stay curious（好奇的）.