Human height : everincreasing ?

[McCrunchy]

Hello,

 

I had a look at graphs of average human height as a function of time , cf for example http://tpek2005.free.fr/Pages/Taille.htm .

It seems that for most populations, height has been increasing almost monotonically for the past 2 centuries.

 

I was wondering : will humans ever reach an optimum "plateau" height ? Or will they just keep growing ?

 

There are lots of factors explaining why we should grow taller (attractiveness, health, etc.) or stop growing (heart has to do more effort to pump the blood etc.) ; more specifically, I am looking for a study of an animal's (any animal) size evolution - this would in my mind provide the best clues to answering this question.

 

Thanks for your input,

 

 

McCrunchy

[SH3RL0CK]

Clearly, there is an upper limit on height.

 

Rather than look at just evolution to explain the increase in height, you should examine other factors such as better diet and healthier lifestyles.

[Mokele]

In general, animals grow larger in captivity, even if they're collected from the wild when young or as eggs, and it happens far too quickly for evolution to play a part. Unfortunately, I'm most familiar with this in reptiles, which aren't a great analogy because they have indeterminate growth (they never stop growing, though the rate slows once they're mature).

 

One point worth making is that averages in the past were a mix of the wealthy (high nutrition, lots of food, etc.) and poor (low nutrition, little food, etc.), with no real middle class. Now, with an abundant middle class and a better standard of living for the poor (at least in western countries), everyone gets better food.

 

Evolution will take longer, a lot longer, especially with a population as huge as ours.

[Mythranil]

Sadly, even with lizards, indeterminate growth has a limit too. As we see with most cases of land-based gigantism, the physical constitution of our skeletal structure and cardiovascular system cannot sustain the strain of that much weight under the effects of our gravity. Godzilla could not exist because he'd have lung and/or heart failure even before the Japanese shoot him down. Now, with water-based creatures, it's a whole other matter - it seems odd that gigantism hasn't occurred more frequently in the oceans than it has.

 

On a side note, I've often wondered if the cause for the dinosaur gigantism was a shift in the natural gravity field of the earth. Don't know what would cause this, and I never bothered to look into it, but it had been a thought.

 

It seems that examples of human gigantism meet a similar fate as our Godzilla. At some height of roughly 9 feet, our systems - in their current configuration - cannot take the strain.

 

I think that, if human evolution (outside of height) ceased, our average height would plateau, assuming our food supply and environmental conditions also cessated change. Both situations are improbable and, more likely, impossible. If it's a greater advantage for humans to be taller, we will first have to evolve our body plans and cardiovascular systems to be able to sustain our increased size. Note, too, that the human brain can only control so many facets of the overall human body; nerve functions require a lot of processing power. Our brain size may have to increase before our body size can increase as well.

 

As for human growth trends - I think humans have artifically altered our evolution by creating stable food sources. In the Americas for example, a constant supply from the same food sources seems (in my opinion) to have caused our younger population to grow taller and more robust. I went to school in a rural community where the average height of the population was, say, 5' 8" in men; later on, in high school, we were mixed in with the taller populations from the city who averaged closer to 5' 10". Now, when I go to my kids' high school, it seems like the average height of males is much closer to 6' 0". I don't see how natural evolution, punctuated or not, could produce that much of a height differential within two or three generations. To me, that's clearly a product of societal changes with regards to our food supply.

 

I think I got sidetracked, but hopefully addressed some of the topic...