Originally Posted by Rajon Rondo
No there shouldn't, its no secret that as people have evolved over time they have gotten bigger.
It is not evolution which causes the gains in size. It is health care, nutrition, etc.
The average height of a Englishman actually declined 3 inches between the 12th and the 18th centuries, according to John Komlos. The cause was poorer nutrition apparently caused by the Little Ice Age stunting crops. Cold, hard winters and early frosts tend to reduce food stock.
Americans also had a reverse in the 19th century due to urbanization. Folks on farms not only had plenty of farm products to eat, but access to plentiful game. City folks were less well fed and so smaller.
Will there be a reverse in the future? It is possible. I can think of two possible causes:
1--better medical care. Komlos sees a shorter population as a sign of poorer medical care, but to some extent the reverse might be true. If premature babies survive because of good care, there are likely to be less healthy through life and so probably will be shorter and pull down the average height in adulthood.
But I think most would take 60 fairly healthy years at three or so inches below the average height to dying in the first day or two after birth.
2--birth control--has allowed folks to put off having children until later in life. This might be wonderful for partying during your salad days, but is a health disaster for the children. Stats show that babies born to older mothers have many more health problems. And dad is at fault also. It seems sperm deteriorates with age and so an older father passes on many more genetic defects than his younger self would.
This factor already shows for folks at 30 versus 20, but becomes a very great problem when the parents pass 35 and from there on it is all downhill.
So I can see how the effects of birth control elevating the age of parents might in the long run lead to a shorter (and more sickly) population.