But this did not happen. Instead, all segments of the population--rich and poor, from small and large families--increased in height. Thus, natural selection, the process whereby differences in reproductive success account for changes in the traits of a population, does not explain why we are taller.
If evolution doesn't explain height increases, what does? Most geneticists believe that the improvement in childhood nutrition has been the most important factor in allowing humans to increase so dramatically in stature. The evidence for this argument is threefold:. First, the observed increase in height has not been continuous since the dawn of man; it began sometime around the middle of the nineteenth century. In fact, examinations of skeletons show no significant differences in height from the stone age through the early s.
Also, during World Wars I and II, when hunger was a frequent companion of the German civilian population, the heights of the children actually declined. They only recovered during the post-war years.
Such data are consistent with recent research indicating that slow growth induced by temporary malnourishment can usually be reversed. Chronic underfeeding during childhood, however, permanently affects stature and other traits, including intelligence.
Second, the trend toward increasing height has largely leveled off, suggesting that there is an upper limit to height beyond which our genes are not equipped to take us, regardless of environmental improvements. Interestingly, the age of menarche, which is also influenced by nutrition, has shown a corresponding decrease over this same time period. In this episode of AsapSCIENCE , the boys run through some of the most exciting scientific breakthroughs that are being made today in order to propel our species into the future.
First off, we humans have a reason to be as smug as we are - our brains are so good, even the most advanced computer system doesn't even come close. In fact, in researchers used the K computer in Japan - one of the most powerful computers in the world - to simulate human brain activity, and it took , processor cores, 1.
As reported in the book Height, Health, and History , the change in average adult male height in the United States over the last three hundred years did not follow a simple trend. From around to , the average height of adult American men remained effectively at around cm. Over the next sixty years to , the average height actually dropped from cm down to cm. Then over the next forty years to , the average height climbed back up, reaching the value of cm.
The average height of adult American men today is still cm. We can take a few things away from these numbers. First, there has not been a smooth trend in average height change over the last years in the United States. For most of this period, the average height has either stagnated or dropped. Only during the brief forty years leading up to the Great Depression did the average height see rapid increase. Therefore, in the United States, an increase in average height is neither steady nor inevitable.
Secondly, Americans today are not really that much taller than Americans during the 's. Three centimeters is less than the diameter of a golf ball. The research revealed that the literal ups and downs of individual human height closely track variations in two factors: diet and disease.
Particularly, where these two factors are at work during childhood. If children do not get enough food to eat or cannot absorb nutrients because of diarrhoeal illness, say, their chances of sprouting into their full potential adult height are greatly diminished. History is replete with examples of this height-health link.
People could thus grow relatively tall, with Englishmen just 4cm on average shorter than their fellow countrymen today.
Credit: Getty Images. But in 17th Century Europe, heights hit a low point. The average Frenchman then stood no taller than cm. Severely cold winters, due to the Little Ice Age , slashed crop yields. The 18th Century Industrial Revolution, which saw people packed into disease-ridden slums in cities, similarly stunted the populace.
By the latter part of the 19th Century, though, the social upheaval had borne the fruit of improved agricultural production, running water and urban sanitation, as well as expanding economic prosperity. Western Europeans shot up the growth charts, and kept doing so for decades.
This height-health link is still starkly visible today. For a modern day example, look no further than North and South Korea. North Korean adult male height lags 3cm to 8cm behind the equivalent figures for their South Korean counterparts, whose country holds the HDI's 15th spot as of How have Northern Europeans pulled ahead? Komlos strongly believes that unequal access to nutrition and healthcare in the US compared to more socialised systems in advanced European nations is the difference-maker.
Millions of Americans lack medical insurance and do not see doctors regularly. Pregnant women are afforded little aid in the States, whereas in Holland, "they get home visits from nurses absolutely free", says Komlos. In addition, a third of Americans are obese, thanks in part to eating too much junk food. Calorie-dense, processed foods can shave centimetres off consumers' growth, owing to developmental and metabolic issues.
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