If humans are becoming taller, it is because of better nutrition and child health care. It is not due to evolution.

This is a difficult question because the trends vary depending upon the region of the globe. Where medical care and proper nutrition are readily available, growth trends are rising. Where there is an absence of these, growth trends decrease. More so than evolution, as Encyclopedia John stated, nutrition and health care play a major role. "Until the general rise in human health the general trend was as urbanization increased height declined." I did find some information regarding growth trends. It seems that height is increasing by 10-30 millimeters per decade in most European Countries. http://www.ingentaconnect.com/content/cabi/pns/2000/00000059/00000002/art00017 The following is an excerpt from http://en.wikipedia.org/wiki/Human_height: "Growth and height have long been recognized as a measure of the health and wellness of individuals, hence part of the reasoning for the use of growth charts. Genetics is a major factor in determining the height of individuals, though it is less influential in regard to populations. Average height is increasingly used as a measure of the health and wellness of populations. This is attributed as a significant cause for the trends of increasing height for egalitarian populations where medical care and proper nutrition are more equally distributed. Diet, exercise, fitness, pollution exposure, sleep patterns, and climate are other possible factors. The relationship between genetics and environment is uncertain. Certainly there are substantial relationships in the general heights of biological families; and the heights of parents and family are a fairly good predictor for the height of their children. However, as cited, there is strong environmental influence as well. Asian populations were once thought to be inherently shorter, though it now seems that humans as a species probably have a similar genetic height potential, and it is clear that genotypic size has not yet been realized." Check out this link as it also has a chart of average height/country.

According to numerous national surveys, Americans today are an average of 1 inch taller than they were in 1960 (last generation, apprx). According to "1001 nights" (bka "Arabian Nights"), which were written circa 1200 ce, a woman was considered tall if she reached a height of 5 feet. Armor of medieval and rennaisance nobles was found to be of very limited stature. Yes, humans as an average are getting taller, the mean height of people today might have been considered tall in yesteryears. The number one reason is better knowledge of nutrition. Knowing which vitamins are needed, especially for children, makes all the differance in growth. Also the mixing of genes is arguably another cause. Being tall is a dominant trait, meaning if a short person and a (purely) tall person produce offspring, the odds are 3/4 the child will be tall. Many "breeds" of people are genetically tall (Northern Europeans, East Africans, Oceanics) and their genes falling into the gene pool have led to a spur in the world's growth. Take blonde hair, for example... it comes from primarilly from the Netherlands but we see blondes everyday, and that's a recessive trait. Nordic blood is the reason so many blondes tend to be tall. Being tall is generally considered more attractive than short, no? So tall people begetmore tall people.

IMO the increase in human height is mainly due to the increase in consumption of cow's milk. This is most notably observed in Japan, where the average height has been increasing since they adopted the Western habit of drinking milk - which only happened after WWII.

Better nutrition, vitamins and minerals for most of the developed world. Poor diet and nutrition early in life cause growth and development to slow down. Another factor improving over-all health and growth is personal hygiene. The development of sewers and water treatment plants in most cities has nearly stopped the spread of organisms like cholera and typhoid fever. In general people have much better dental health too, so the developed world is quite healthy. All of this impacts over-all health and growth. Sadly though, much of the developed world’s malnourished and we know the developing countries are starving to death. Having a lot of food doesn't necessarily mean good health and nourishment. In general developed countries do well although poverty exists in developed countries too. Again, awareness and having the means to stay healthy has an impact on growth. Genetics play a large part too.