It's already happened
Go to Willenhall, Coventry. Everyone's about 5 foot tall.
Modern mammals, including humans, could be at risk of shrinking as a result of global warming, just as teeny prehistoric horses shrank to an even smaller size when temperatures rose 56 million years ago. Modern Morgan horse (left) thinks about eating teeny Sifrhippus (right) Modern Morgan horse (left) thinks about eating …
I mean, some of the tallest people I know are from some of the hottest climes, particularly Africa. I always thought being larger helps in hot climates due to increased surface area for cooling.
Also, humans seem to be getting taller with time, statistically speaking. I believe the average height in the UK has been increasing for centuries now ( I cannot for the life of me remember where the status for this came from, but I do remember reading about it).
Then again, they are talking size in weight. I can imagine humans getting lighter, as they need less fat to keep warm, etc... Those Africans I mentioned were tall, but very lean.
Interesting study, none the less.
"It's not the first time that scientists have noticed that mammals seem to be smaller in hotter climates, and have speculated that evolution takes care of this, because smaller animals will thrive in high temperatures because their bodies are easier to cool."
What? Have these people ever been to Africa and Asia? Tigers, lions and leopards vs. lynx? Eland are bigger than moose. African buffalo aren't smaller than bison or wisent. Not to mention elephants, giraffes, etc.
Temperature might have an effect on size, but surely other things like availability of food and other evolutionary quirks like elephants' ears.
Taller, yes, but the number that counts is not height, but volume. I'd give you good odds that there is an evolutionary pressure for some African peoples being tall (I thinking places like Kenya and Ethiopia here), and that this pressure is probably related to why they make some of the world's best long distance runners. I'd also give good odds that whilst tall, their body volume is considerably lower than shorter people hailing from cooler climates.
Yes, but the east africans are tall and skinny, that gives them larger surface area-to-body mass ratio, which helps with cooling. People evolved in cold climates like scandinavian vikings are giant beefy f**kers in all dimensions, hence low ratio of surface area to body mass allowing them to stay cool.
This won't really affect humans that much (or domestic and 'indoor' farm anilmals) seeing the extensive use of heating / air conditioning, but it would affect wild animals. It's likely that few animals will be able to adjust their range by moving north/south to find a more optimal temperature because they'll find humans in the way.
Bulletin, healthy adult humans even today range in size from just under 4 feet to about double that. Their size doesn't depend on whether they got much more or much less sun or water due to their local climate. It does depend, tho, on the level of nutrition they receive while they're growing and whether their genes support potential growth beyond a certain height. Within two generations, humans in general can eat differently and therefore grow to different sizes than their parents and grandparents. And do! Just look around! The idea the entire species would permanently shrink would have to mean their larger sizes would not allow them to live beyond puberty, and the smaller size would. That wouldn't be due necessarily to climate change, as it could have been over a period of many centuries with horses, but would require some kind of mass death of all prepubescents above a certain height. There would necessitate a bizarre change in the environment that would benefit a smaller size. Climate change could not account for that. So the implication in this POORLY written article, by someone who really has little clue to how evolution works, that rising or falling temps would necessarily kill off all tall prepubescants worldwide and benefit much smaller prepubescants, is too preposterous to figure out what kind of condtions could actually cause that.
If there's no protein around, a generation of 6 1/2 ft parents could see their kids grow to 5 ft and no more. Climate change does not imply any such condition. A world of exploding volcanoes would kill off most, and the rest would remain tall IF they had the protein to continue to eat. The conditions of what it would take to shrink human size universally is beyond the understanding of the "author" of this piece. I AM sure about this.
VERY BAD JOB, REGISTER.
The tall Africans drink cow's blood. It's the protein that makes them tall, despite the temps. The entire article is junk. Climate change is real---400 billion tons of ice melt each day at the poles---but the not-so-bright idea the entire species could shrink due to climate change is really dumb, unless all protein disappeared, and the climate that would kill off all protein would kill us off too (we're protein!).
As a wise friend once said to me, "Just because you are sure, doesn't mean you're right"
It doesn't imply any such mass wipeout of tall people: that *would* be a nonsense. What it means is that over many generations, taller people would be less likely to reproduce, leading to a gradual reduction in the average size of members of the species. Obviously,
How might this come to pass? Well, given the self-evident tendency of surface area per unit volume to decrease with increasing volume, larger animals find it more difficult to remain cool if the temperature increases - not impossible, just more difficult.
That implies less activity for larger animals, since activity produces heat that - unless removed - might cause dehydration/heatstroke/.... Less activity implies a reduced ability to support a family than a smaller but otherwise identical animal (less foraging time, smaller hunting range, or ...). Smaller families for (genetically) larger members of a species leads to a gradual diminution of the average size of a species as a whole.
Doesn't sound too implausible to me.
Yes, taller because they have longer legs usually. Short legs (like Europeans') are a cold weather adaptation. Long legs lose heat quicker. House sparrows were introduced with European settlers to North America and now now the further south you go in the USA, the longer their legs.
This article is rubbish as far as any human implications go. The timescale is too short to have any effect on human evolution and countervailing trends (not the least sexual selection by women of taller men) put pressure in the other direction.
Read Chapter 5 of "Life's Grandeur" for the fascinating complexity of equine evolution. To vastly oversimplify - the traditional story (developed by TH Huxley) of small many-toed horses evolving linearly via larger specimens with fewer toes up to modern Clydesdales is erroneous. At any given point in time and space there were many different species of equus trotting around - some smaller, some larger; some with fewer toes, some with more - it's just that the surviving examples we find today are of the larger, single-toed variety (and the earliest ones were the opposite).
It may be that warmer climates drove selection of smaller animals, and vice versa, but this would not have been a simple linear process.
Unlike all other animals, we've conquered the environment with intelligence, so physical characteristics are irrelevant.
However we carry over our evolution so birds fancy tall blokes, the tendency is for increase in height. World war two and the welfare state has caused the massive increase in height over the last century, and I see no reason to see it end.
Firstly the war meant that all the dutch are tall because half the dutch women were screwing the same giant of a german soldier, if you're going to fall on your back with your legs in the air for an occupying force, it might as well be for a tall one. The same is true for all the HausFraus in the 50s, with the yanks.
Secondly, the welfare state allows women to screw whoever the want and not worry about how they're fed.
Hey presto, any society where you've conquered the environment and women have a choice, will ensure increasing physical attractiveness. (and intelligence, because stupid men can't get laid, because they're poor.)
Not sure it guarantees intelligence. If you guarantee the survival of all sprogs, then thick chav slappers (of both sexes) who get too pissed to use a rubber are going to out-sprog intelligent couples who take a more planned approach. And thick ultra-religious nutters who believe you're destined for hell if you use contraception are also going to out-sprog intelligent people.
A little overgeneralistic, but I would also add I've noticed a correlation between facial beauty and breast size in women. A beautiful woman doesn't need big jugs to attract a mate, though it helps!
However, it remains to be seen whether 'conquering the environment' is an intelligent thing to do - it in no way guarantees long-term survival. Pity none of us will be around to observe the consequences.
Our "intelligence" has caused a population explosion, environmental imbalance and host stress that most viruses would envy.
Ah well, nothing new here folks - Christian Bergmann noted back in 1847 that mammals tended to be smaller in warmer climates than than individuals of the same species in cooler climates:
"Über die Verhältnisse der Wärmeökonomie der Thiere zu ihrer Grösse".
This is in the long term and as the saying goes, in the long term we are all dead so the correct response here would be 'meh'.
Warm blooded animals need to lose heat to the environment at a controlled rate. Two factors govern the rate of heat loss - the temperature difference between environment and body, and the body's surface area to volume ratio.
As the temperature of the environment increases, the heat loss decreases, as the rate of heat flow is proportional to the temperature difference - in other words if the environment is ten degrees cooler than you, you lose heat twice as fast than if it is only five degrees cooler. If the environment is hotter than you, you're in trouble.
The body generates heat at a rate that is proportional to the volume, in other words an animal twice the size will produce twice as much heat. However, the heat loss is through the body's surface, and doubling the volume of an animal does not double the surface area. This is why large animals tend to have wrinkly skin, to increase the surface area, and also why elephants have big ears (nothing to do with Noddy not paying the ransom).
In short, bigger animals lose heat slower than smaller ones, so in a warmer environment, there is a selective pressure for animals to become smaller to lose heat faster.
I'll repeat this as you obviously missed it:
Elephants are large and the Serengeti is damn hot.
I've never seen a camel the size of a chihuahua and it gets over 50 celsius in the Sahara.
These are both mammals the last time I looked or has taxonomy taken some weird twist and classified them as cephalopoda while I was holidaying on the Moon ?
This paper deserves star billing on http://www.badscience.net/ as it's complete and utter crap.
To respond to your two points:
Elephants, and other large animals living in a similar environment have specific adaptions to cope with the need for increased heat loss - in the case of elephants and rhinoceroses, these are large skin surface area, increasing the surface area to volume ratio, and a propensity to seek water to cool down in - direct heat conduction through water is much more efficient than through air. The other large african land mammal I can think of is the hippopotamus. No prizes for guessing how they keep cool. Note that the number of species of large african land mammals is small (I can think of 3 of this scale), whereas the number of species of small animals is massive.
Camels have a number of specific physiological adaptations that allow them to raise their body temperatures above that of other mammals, thus maintaining a higher rate of heat loss:
Note that pretty much all of the other mammals living in deserts are very small and subterranean - e.g.hamsters.
Wow Wikipedia, that bastion of accurate and scientifically validated information.
Ever wondered another damn good reason things are small in the desert ? Very little food.
Large African land mammals:
Lion, Zebra, Rhino, African Buffalo, Wildebeest, Giraffe and a few more.
“Maybe that’s not all bad and if that’s the worst it gets, it will be fine. You can either adapt, or you go extinct, or you can move, and there’s not a lot of place to move anymore, so I think it’s a matter of adaptation and becoming smaller.”
As someone of Anglo-Viking ancestry, I find this racist and plan to kill the wanker via the Flying Eagle! Hand me the battle axe. Or chainsaw.
I hate to go off on the compulsory tangent, but:
"...during the PETM, when concentrations of carbon dioxide in the atmosphere and oceans caused temperatures to get hotter across the planet"
It's been documented numerous times (unwittingly by none other than Al Gore - he evidently either didn't look at the charts he displayed in his movie very closely or he assumed we were too stupid to notice) that the CO2 levels increased AFTER the temperature rose, not before. Saying over and over again that CO2 caused warming during this period doesn't make it so. The strategy, it seems, is to simply make the subliminal correlation enough times in casual conversation so that it becomes pseudo-intuitive ('everybody knows that!'). *** Note that I'm not saying that CO2 does not cause warming, only that the most often cited segment of the historical record doesn't support it. Using faulty data to support a position merely undermines that position.
The HUMAN RACE - If Global Warming is Not REVERSED Soon - Will SHRINK from 7 Billion to about 144,000 - FIRST will be FAMINE Then when a Billion Refugees spread PESTILENCE and the Food Riots Start there will be Nuclear WAR and - for MOST of Humanity - DEATH. The Four Horsemen of the Apocalypse galloping towards us in Ten-Gallon Texan Cowboy Hats. http://www.theregister.co.uk/Design/graphics/icons/comment/pirate_32.png
Evolution is not *just* a product of temperature, but many things. The basic rule is that cold temp = low surface area : volume ratio. Think polar bears, whales etc. Penguins attain the same feat by behaviourl means (huddling) - the group has a small surface area compared to its volume. On the other hand we get things like meercats, hamsters, gerbils etc that are desert creatures which are tiny little things.
The large African animals referred to like elephants, hippos, lions etc don't live in the desert. They live on the plains where it is rather cooler. They also have various mechanisms that help them deal with the heat, which are either things that increase their surface area : volume ratio (huge ears for example) or are behavioural (like sitting in water, spraying themselves with water etc). The reason they are larger are the other benefits of size such as the ability to avoid predation (kinda hard to bring down a bull elephant with just your teeth).
The Masai still have a pretty high ratio due to them being very slim. Therefore their height alone is irrelevant for this purpose - it's their height *and* their build we need to consider.
Furthermore tallness granted them the ability to see danger from a greater distance. Therefore, the tall fat ppl and the short ppl didn’t get to pass on their genes. On the other hand the tall skinny folk were more active, having a higher surface area : volume ratio and could see things from afar much more easily being able to see over the grass.
If there weren't so much tall grass the Masai would be short, but there are other factors than just temp that affect the likelihood of being able to pass on your genes. Compare with the tiny ppl from SE Asia, esp the islands. There’s no real benefit to being tall if you live in the jungle - the trees will always be taller than you. Therefore heat becomes a larger factor and you get 'ickle ppl.
I've spent a bit of time with the Maasai and the Datoga. The men are generally a little over 6' tall. They're certainly taller than average (particularly when compared with some of their neighbours), but I have no idea where you got the idea that they're all basketball giants. The main reason they are tall is that they have an unusually rich and high protein diet through childhood.
Is the discussion on potential implications towards humans intended to be really misleading or is the author clueless?
Assuming that the science here is spot on (and new scientific understandings never occur with one study):
1. A significant evolutionary response is likely to take tens of thousands of years.
2. This response would require that we don't use air conditioning, we don't move, and technological change stop immediately in medicine, in areas that improve conditions for child development, and in reducing the cost of living generally. Historically low technological changes alone lead to the cost of living dropping by more than a factor of 7 in only a hundred years, let alone thousands.
willingness and cooperation (lots)
money and technology (lots)
oil (lots and lots and lots)
USA is already eating the 3rd worlds food capacity (in terms of the above resources). If the 3rd world progresses to the same level as USA then as surely as rabbits on an island will run out of food at a given population size, then so will we.
However, we will run out of water first.
Large populations evolve more slowly than small ones. At 7 billion, the human population is incredibly large, probably larger than any mammal population in the past. So we're not evolving anywhere very fast at this point.
This could be changed either if the human population overall shrinks substantially, or if we stop traveling around the globe (which we've been doing, as far as evolution is concerned, for the past 30K+ years). Neither is very likely in the near term.
The oxygen levels were alot higher in prehistoric days (known fact) and it is this decline towards the levels we have now that was a factor in size reduction in animals. As also noted in insects.
Now we might have to get smaller to be able to sit on the next generation of public transport seating, which gets smaller and smaller each year that by 2025 I expect my kneecaps to be in my face.
Either way give me a Victorian ceiling hight over the claustrophbia inducing ceiling we have today
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