A human male can be 4’10" without it being pathological.
A human male can also be 6’10", over 40% taller, without it being pathological.
And I’m being overly restrictive here, I imagine the medical definitions for dwarfism/gigantism lie well beyond these measurements.
Why do these differences occur in humans? You never see an adult male elephant that’s 40% longer or higher than another one. You never see an eight-foot Labrador. I imagine it happens in snakes and spiders, but I can’t think of cases in other mammals (that aren’t caused by selective breeding, which is why I won’t compare alsatians to chihuahuas or drag pygmies into the equation). Why not? Why humans?
Well height in industrialized countries increased as more and more portien was available. Look at door in 13th, 18th and 19th century castles and forts. The average makes me duck my head some times (5’6").
Other animals are not able to eat to excess as humans are.
I cannot think of another species that has the same range as humans. The worldwide distribution, economic factors, environments mean that lots of variables are introduced in determining size.
How many adult male elephants do you see in a day? I’m not so sure that such variability does not occur in other species.
You never see an eight-foot Labrador because a Labrador is a product of artificial selective breeding. If such a dog were ever produced it would probably not be mated with another one. That characteristic would be suppressed, because it is not in compliance with the standard for the breed.
Note that dogs, as a whole, all belong to the same species. When you think of it that way the size variation you get in humans is nothing, dogs range from poodle to St. Bernard, which is like a thousand percent difference. Of course, that’s the result of artificial selective breeding, but it still puts humans to shame.
To some extent, evolution has determined body shape for some populations. A cold climate favors a shorter, stockier build to conserve heat (think Inuits) and a hot, arid climate favors a tall, think frame for the opposite reason (think Masai).
Nutrition also plays a significant role, as can be seen in the significant increase in height of Japanese born just before WWII and those born in the afluent 70s/80s and beyond.
I’d also speculate that growth can be affected by simple mutations in one or two regulatory genes (that turn processes on or off at certain times) and that height hasn’t been a significant factor in many societies for thousands of years. Thus, these genetic changes get perpetuated without any real weeding out.
Donut’s point about dogs is well taken. Remember that most breeds of dogs have only existed for a few hundred years, so it’s not all that hard to get a non-human mammal to exihibit fantastic size varitation in just a few generations.
Gigantism and dwarfism are not quite the same in that gigantism is defined by size relative to the heart, rather than strictly by size. An abnormally large man with an abnormally large heart (and other organs to match) would not be “suffering” from gigantism.
A number of famous large humans- Andre the Giant, for example- were afflicted by gigantism, and generally their lives are cut short by the extreme strain on the circulatory system produced by the extra distance.
Sorry, I missed something there… gigantism doesn’t actually relate to height at all, but to enlarged features- hands, feet, mandible… find out more here> http://www.medstudents.com.br/endoc/endoc8.htm
Housecats have a pretty wide size variation. I’ve got a seventeen pound cat sitting right next to me (and he’s not fat…just a big cat) I’ve seen plenty of full grown cats that are maybe half his size.
I don’t think we have a greater variation in height than other characteristics, physical or otherwise, e.g. weight, intelligence, nose shape, psychological makeup, hair, skin color, etc. All in all, we’re a pretty diverse species.
I would suggest that the artificially-selected range in dogs, for example, would not remain if not reinforced by humans. The huge breeds like St Bernards, for example, tend to have a short lifespan as compared to normal sized dogs; they are prone to all kinds of problems including hip displasia and (ugh) twisted stomach. Aren’t some really, really tall people subject to back problems, also?
Besides the environmental influences, human variability has much in common with domestic animals’ variability.
Ie, wild antelope, buffalo, wolves come in pretty much one standard color each, but domestic goats, cattle, dogs, (and chickens, cats, horses) come in many color variations. Same for size and wooliness (there are curly-feathered chickens and curly cats and sheep and people), maybe some other variations.
The color of a horse doesn’t usually affect its utility, but people are likely to select such a sport and propagate it. The first blonde human sport might have been treated in one village as, ewww don’t want to marry that, but in another might have been seen as special, the most desirable marriage partner.
Note cultural issue causing new coloration or size to have prestige and desirability in specific groups, leading to groupwise gene selection.
So humans’ conscious choices seem to have propagated variabilities in both themselves and their domestic animals.
I don’t think our size variation is all that unusual. A great deal of size variation is present in a lot of widely distributed species. For instance, this blurb on the coyote, Canis latrans:
Some of the crows around the Bay Area suburbs are freaking enormous, but as near as I can tell, are the same species (Corvus brachyrhynchos) as those I remember from back in rural PA, which were a lot smaller.
Good point, Dr_Paprika. I think CookingWithGas gave me the best answer when he asked how many adult male elephants I saw in a day. I checked out elephant sizes and the males do in fact vary in size up to 50%. So there’s another mystery out the door, or as we say in Calcutta: Garbage in, garbage out.
Far from being a genetically diverse species, humans have an unusually homogenous genome.
We are all very alike, more so than the comparitively diverse chimpanzees, for example, and such phenomena as height and coloration are expressions of very few genes.
Plenty of fish do not continue to grow; they have a short lifespan and/or will only get so big even if they live unusually long. You won’t see a trout-sized guppy even under the best of conditions, and even very long-lived fish still remain within a certain “normal” size range for their species… you could have a 20 year-old lake trout that’s 3 feet long, or 4 feet long - not 7 feet long unless something is freakishly wrong with that fish.
However the continued growth property of some fish mostly goes unused and therefore out of sight anyway. The most common way for a fish to die is by predation; most fish get eaten as juveniles, most of the rest get eaten as adults. Very few fish die of “old age”, so they almost all get eaten before they can grow to their maximum sizes. It’s usually a combination of these lucky few old-timers and those genetically big boys with a good food supply that end up hanging on people’s walls as trophey fish - but this size range is still natural and normal.
The continually growing things sort of reminds me of bits that I’ve read about people’s noses and ears continually growing after the rest of them stops, so you end up with some old people who look a little funny. Whether it’s true or not (haven’t seriously looked into it) it illustrates the point - my ears/a fish might continue to grow for 50 years, but my ears/the fish will still be recognizeable as what they are and within a certain predictable size range… just a bit bigger than average.
