Answer by John Mackay and Diane Eager
Most of us have noticed that if mum and dad are tall, their children are taller than average as well. Tall people tend to run in families even though occasionally a short offspring will be born. Likewise if you have a short mum and dad – you can usually forget about becoming a basketball star, as you will rarely be taller than average. It’s a fact that the average height of any population of humans is determined by a mixture of genes and the environment they grow up in. Humans grow until their mid to late teens, and if because of a poor diet, disease or other stresses they have not reached their maximum genetic potential by then, they will not grow any taller. However, they will pass on their height genes to the next generation, where it has been observed time and time again that if that generation grows up in a better environment, they will be taller.
A good example of this phenomenon is seen in the Vietnamese who migrated to western countries after the war in Vietnam. The original migrants moved to the west as adults, and those who were welcomed to Australia were mostly short compared to us Aussies. They had grown up on a poor diet in a war ravaged, disease ridden environment. But their children have grown up in Australia eating a relatively high-protein western diet, protected from many tropical diseases, and free from war and strife, and they are significantly taller than the original Vietnamese migrants. If however western countries were to experience a complete collapse of their economies, and people were reduced to scraping a living on a poor diet and unable to afford health care, that generation will be shorter than today’s average. War does this as well where history tells us that the average height of French peasants decreased by almost 10cm after the Napoleonic wars because of Napoleon’s habit of throwing huge blocks of mostly big county farm boys at the opposition until sheer numbers won the day.
None of these changes are evolution. A good diet and a good environment and lack of war cannot and will not make you taller if you have inherited genes for short stature. That’s true for humans, cows or Koalas. But just as true is the fact that natural selection via climate and food supply will eliminate any unsuitable sizes and shapes just as efficiently for humans as for kangaroos and crocodiles.
Consider the following: After man’s dispersal from the tower of Babel (Genesis 10-11), humans of all shapes and sizes spread out over the world and settled in widely different environments. The Eskimos /Inuit, who live in the usually freezing Arctic tend to be short and chubby, simply because any tall skinny ones died of the cold ages ago. The opposite is seen in hot regions of Africa you find tall thin Zulus, simply because tall thin people have a greater surface area for their body mass and lose heat easily. Short fat ones got heat stroke and died. Short thin pygmies on the other hand not only survived the heat, but they could easily hide in the jungles from their big tall Zulu ancestors so big enemies couldn’t find them to kill or eat them.
These are real examples of survival of fittest in particular environments, but none of them are examples of evolution. Natural selection has had a marked and provable effect on human size and shape. In both cases the populations did not evolve their body size. Genes for the least appropriate body size have been eliminated. That is what natural selection does – it decreases the gene pool, which is the opposite of evolution.
Some variations in human size are degenerate i.e. gigantism and pygmies. How do we know? Human growth is also determined by the functioning of an internal clock that stops the production of growth promoting hormones at the appropriate time. While that stays switched on you continue to grow. In most cases the clock will switch off in your late teens, and from then on you cease growing vertically (although you can still grow horizontally, much to many people’s frustration). But if the growth promoting gland fails to turn off then you will continue to grow, to your own detriment. The growth clock is a safety valve so that your body weight, which continues to increase with your height, doesn’t become a danger to your life. There is a limit to how tall the human body can grow without putting too much strain on the bones, joints, muscles and heart. Most giants are impressive when they are 25 and dead when they are 45.
The pygmies in Africa are at the other extreme. Their growth clock switches off much earlier than normal, when they are around 10 years old, and unless you can retrigger it, they will remain at the height they reached at age 10. They will still undergo the other changes in body structure needed for adult life, such as developing secondary sex characteristics. It is interesting to note that pygmies are descended from the tall Zulus, but genetic mutations have prevented them from growing to normal height. Neither gigantism nor pygmy formation are evolution. They serve as reminders that mutations are real, but they do not produce evolution, and the real history of man is creation followed by degeneration, overlaid by the eliminating effects of natural selection.
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