Evolution - Giants Taking Over?

You study the growth in the height of humans. How tall are we going to be in the future?
Frank Rühli: Based on roughly 150 years of compulsory military service, we have a very good database for Switzerland, and we also have access to microdata from up to 90 percent of all men aged 18 to 21 years of certain birth years. This includes information on height, body type and weight. These data can even be broken down into individual districts, allowing us to compare cities, for example, Zurich and Basel. Until approximately 2010, the Swiss had continued to become taller, on average by an impressive 15 centimeters. We have now arrived at an average of close to 1.80 meters.

We were wondering, does body height always correspond to shoe size? Tall people – large feet?
Yes, this correlation exists in principle. If you are taller, the long bones that are found in your extremities will also be longer, as well as the metatarsus and the phalanxes. To a certain extent, body height correlates with shoe size; however, a tall person will not necessarily have the corresponding large feet, and a shorter person will not always have small feet.

Back to the Swiss: is a height of 1.80 meters considered tall when compared to other countries?
In comparison on the international level, this is actually quite tall. The record holders, however, for men as well as for women, are the Dutch, at 1.83 meters for men and 1.71 meters for women. Even if there are differences, the Swiss data can be applied in part to other Nordic countries such as Germany, the Benelux countries, and also northern Italy. Body height is dependent on, among other things, social status, income, access to health care and nutrition – factors which are quite similar among the Nordic countries. Continuous malnutrition has a negative effect across generations; the human body does not receive sufficient nutrients to invest in growth with respect to height. These are the reasons why Switzerland cannot be compared with countries in the poor regions on Earth.

Your data concern exclusively men. What about the women?
Our research is based on data from the Swiss military where the proportion of women is known to be small. Of course, these days, more and more women volunteer for military service, but it is still a modest number. Those women who volunteer typically represent a group that meets a certain physical standard, which means that they are not representative of the general population. These data are thus sparse, and they also do not reflect the past. The data that are available to us from the past are derived from passport applications dating back to the 19th century which sometimes include information on height. But even here, the data do not represent a good average of the population, as only people from the upper strata of society possessed a passport – those who could afford to travel and better-quality food, and who were thus more likely to develop in healthy ways. The same is true for long-bone data from cemeteries: who was buried? Unfortunately, data that were not compiled in the past cannot be generated later. Thus, we in Switzerland can only make solid statements about the male part of the population. We do assume, however, that the body height of women has developed in a similar way.

You mention factors like social status and access to health care which have an influence on growth in humans. What else influences our height?
Generally speaking, tall parents will have tall children. It has been discovered that there are genetic markers – known as Single Nucleotide Polymorphisms (SNPs) – for body height and growth. The stronger they are represented within a population, the taller the people will be on average in this region. Besides the factors already mentioned, consistent physical as well as psychological stress will impact how tall people in certain regions in the world will grow. In countries where political suppression is commonplace and a free, self-determined life is not possible, people tend to be smaller. Several studies by Australian anthropologist Maciej Henneberg from the 1990s prove that people in South Africa have been growing taller since the end of apartheid.

Is there a connection between body height and health?
Due to genetic factors, it is probable that height has an influence on the prevalence of certain diseases. Evidence to this effect has been compiled in a study by the team led by physician Sridharan Raghavan at the University of Colorado, published in the journal “PLOS Genetics”. According to this study, certain illnesses will be more or less prevalent according to body height – for example, the increased risk of atrial fibrillation and varicose veins in tall people. At the same time, the study states that tall people carry a decreased risk of coronary heart disease, high blood pressure and high cholesterol. Short people, on the other hand, have an increased risk of type 2 diabetes.

What does the future hold: will we grow taller and taller?
Interestingly enough, the increase in human body height has – at least according to the Swiss data – reached somewhat of a plateau over the past ten years. This means that we are not currently seeing significant growth in height, but rather a growth in width. People are gaining weight, and this applies globally: nowadays, there are more overweight people than people who are malnourished, also in countries like China, Saudi Arabia or Egypt. One- quarter of all 19-year-old Swiss people are overweight – it used to be exactly the other way around. Excess weight is a big problem. One other factor that may have an influence on the current plateau of body height: Switzerland is a country of immigration, and the military does not differentiate between the country of origin of a person´s ancestors when compiling data. Finally, it is also possible that we have reached a kind of genetic limit. We will continue to grow taller, but only in very small increments. Most likely, humans are not genetically predestined to grow three meters tall.