快猫短视频

Read more: 鈥�Secrets of the body鈥�

IT DOESN鈥橳 take a scientist to spot that human bodies are all a variation on a theme: one head and for the most part the same number of limbs and organs in the same places. But we clearly come in all shapes and sizes. What鈥檚 more, the template for our bodies has changed over the course of our evolution and is still changing today. So how variable are modern humans and why? What aspects of an individual鈥檚 body are unique? And what will future humans look like?

None of our physical attributes differs more obviously than stature. There is almost half a metre between the height of the average man in the shortest population in the world, the Mbuti tribe in the Democratic Republic of the Congo, and the tallest, the Dutch (1.37 metres and 1.84 metres respectively). Between them lies everybody else. For people of European descent, the average woman is 1.65-metres tall and the average man is 1.78-metres tall (see diagram).

Differences in height stem from a complex mix of our genetic heritage, overlaid with the effects of nutrition and health in early childhood. The genetic influence can be traced way back. Our ancestors living on the plains of Africa 1.9 million years ago were tall 鈥� around 1.83 metres 鈥� with long legs and narrow bodies, adaptations that may have helped them keep cool while travelling long distances in search of food. As humans migrated towards the poles, however, they evolved shorter and stockier bodies with broad ribs and pelvises 鈥� perhaps to reduce the surface area from which heat could be lost. In the tropics they evolved the smallest bodies of all, possibly to reduce heat production in the first place.

Although these general patterns still hold, a much better predictor of your height comes from looking at your immediate family. Genetics accounts for 80 per cent of the variation (Nature Genetics, vol 40, p 489), with over 50 gene variants that link to height found so far. The other 20 per cent is down to nutrition 鈥� particularly in the first two years of life 鈥� and whether the body had to divert energy to fight disease when it should have been growing. This 20 per cent largely explains why . The average Dutchman, for example, was 16 centimetres taller in 1990 than in 1860 thanks to improvements in nutrition and healthcare. Still, the rate of growth in healthy, well-nourished Westerners has been slowing for decades, which suggests that there is a limit to how tall our genes will allow us to be under perfect growing conditions.

鈥淭he average Dutchman was 16 centimetres taller in 1990 than in 1860鈥�

If height is variable then weight and body shape are even more so. According to one estimate, weight varies around the world by as much as 50 per cent, even if you leave the shortest pygmy populations out of the equation . Wherever you go, though, the trend is moving towards the same shape, and not a particularly healthy one. Belly sizes are increasing worldwide. , including Bangladesh, Guatemala and India, found an increase in average body mass index. Most of the growth came from wealthier people getting fatter more quickly rather than poorer people getting less thin.

Measures of BMI may actually underestimate our expanding waistline. A 2002 study found that while children were about the same weight for their height in the 1990s as in the 1970s, they actually had 23 per cent more fat. This was offset by a reduction in muscle mass of 3.2 per cent indicating that we are also getting punier (). The only good news is that figures from the US, UK, Spain, Sweden and Switzerland suggest that rates of . An ever more wobbly human race may not be a foregone conclusion after all.

Whatever the future holds for our species, it is comforting to know that there are still myriad ways in which each of our bodies is unique. Studies of twins have found that even when two people begin with the same genes, they start to differ almost immediately. Not only do their genomes diverge along their own path because of random mutations, copying mistakes and epigenetic changes, but a twin鈥檚 unique environment in its part of the mother鈥檚 womb can alter the way its tissues grow and develop. Add to that the fact that many body parts owe their shape to randomness as much as genetics and the potential for variation is huge (快猫短视频, 28 July 2012, p 32).

Take your iris. The complex mesh of muscles, ligaments and blood vessels in the eye is unique thanks to the random way in which each eye develops. As a result, your two eyes differ from each other as much as they differ from everyone else鈥檚. , making iris recognition one of the most trusted forms of biometrics.

In fact, most of the research on variations in the human body has so far concentrated on complex features that can be used for biometrics. As well as iris patterns, these include the dimensions of the face, shape of the ears and, of course, fingerprints. But chances are that your individuality extends to everything from the shape and size of your belly button to the position of the organs inside your body and the placement of your nipples on the outside.

As a species, we may have become taller, wobblier and weaker, but at least each of us can take solace in the fact that, individually, we are as unique as ever.

This article appeared in print under the headline 鈥渋t takes all sorts鈥�