The end of the great Australian growth spurt

Plentiful food and good health don’t always lead to increased stature. patriziasoliani

Over the past century most generations have grown a little taller than the last. Believing this growth was a result of improved nutrition and better health care, we have been proud of this greater stature and expected our children to grow even taller.

But Australians’ growth is coming to an end. It is likely that Australians will not grow taller in the future, and may even get a bit shorter than the current 175cm for males and 163cm for females.

In fact, the only increase likely to occur in the 21st century is that of body weight, or too much “good nutrition”.

Our ancestors some 3 to 4 million years ago were short, about 120cm tall. Since then our bodies were getting taller until about 100 thousand years ago when they reached levels similar to today.

The growth was a combination of developing a fully erect bipedal stance and expanding body size with the availability of higher quality foods, developed with better technologies.

Bigger bodies also provided some protection against predator attacks. At the end of the Ice Age 10 to 15 thousand years ago people were as tall as they are today - males about 175cm, females about 165cm tall on average.

The invention of agriculture, beginning around eight thousand years ago, produced overcrowded settlements, more food but of poorer quality -mostly carbohydrates instead of proteins, vitamin and mineral deficiencies - and periodic crop failures. Stature reduced by as much as 10cm.

In Ancient Greece and Rome males were about 165cm tall and females around 155cm. We remained short through the Middle Ages and into the beginning of the Industrial Revolution when workers lived in overcrowded urban conditions on very meagre salaries.

It was only in the last 100 years or so that living conditions, nutrition and health care of the majority of people in developing nations improved. This allowed us to fully express our inherited potential for body growth and we have returned to heights of our ancestors 12 thousand years ago.

Height increases over the past 100 years have varied dramatically between countries and even regions. In Europe and some states of America locals have grown 1cm per decade. In Holland the increase was a whopping 15cm during the 20th century, and Poles grew by 12cm.

Closer to home, however, there has been some disappointment. In 1926 Australian women measured 161cm and this rose to only 162.5cm in 2003. The growth of Australian men was less than half of the growth of British males, who grew 1cm per decade.

In some parts of the United states, for example Mississippi, and in Puerto Rico there was no increase observed. So a growth in stature is by no means universal in the present-day world. In fact, developing nations have not yet transitioned to better health which could promote growth.

Some human populations living in very hot and humid environments have adapted to heat stresses by reducing stature. (A big body does not radiate inner heat well and is prone to overheating in tropics). These short statured populations are commonly called “pygmies” and their average height is less than 150cm even when living conditions are good.

Clearly, there is more to body height than just “eat more and you will grow taller”. Studies of families in developed countries indicate that over 90% of height differences are determined by genes. So nutrition and other living conditions can only change our height by a few percentage points, by around 10cm at best.

In everyday language we often talk about stature. Although it means more than just height - a general presence - it is mostly related to height. Like many mammals, a bigger male body elicits more respect among humans.

Studies in Germany have shown that the taller of the two brothers, irrespective if they were elder or not, have more success in life, with better jobs, higher salaries, etc.

Short males are often successful too (think of Napoleon Bonaparte) but they compensate by greater assertiveness.

Larger women may elicit more respect, too, but they are not considered as attractive as shorter females. A study by Cambridge researchers showed short males and tall females had more trouble finding partners than tall males and short females. In this situation most children will have tall fathers and short mothers, so their stature is likely to be average.

We are conditioned to think that bigger is better, but the increase in size has its limits. It is now obvious that increasing body mass is dangerous, but we still do not think the same about body height.

Our body is a mechanical structure. Its tissues have defined properties that can hardly be stretched. Increasing length of bones requires their disproportionate thickening to maintain strength. Growing muscle bulk produces more strength but not in direct proportion. This is why we can’t fly by using just our muscle power - we are too heavy in relation to our strength. Smaller birds do not have this problem.

Moving long limbs requires more coordination against lever arms of bones between joints, and more dead weight of hands and feet that need to be lifted. Giant bodies can be clumsy. Circulating blood around longer vessels against the force of gravity also presents some problems.

Our body length at the moment is optimal for our function. Further growth may produce the phenomenon of hypermorphosis - changing not only the size but the shape of body proportions in order to adapt to a different set of physical requirements. But such changes are unlikely without hormonal additives and genetic engineering.

Although food is plentiful and health care readily available, current lifestyles do not promote optimum conditions for physical development of children and adolescents.

To ensure our height is maintained and our weight does not increase disproportionately, we need to be vigilant about the impact of low levels of exercise and high stresses that result from the overabundance of instant communication and frequent fractures in family life.