Back in the day of the first mammals, horses started out the size of house cats, weighing about 8 pounds and standing only a few inches tall. Then they got even littler, a direct result of the warm temperatures that characterized the Eocene era. Only when Earth cooled down a bit did the beasts get big, according to a new study — the first evidence that temperature directly affects body size. Interesting results when you think about rising global temperatures. Are Earth's animals about to undergo a New Shrinkening?
In about three-quarters of mammals, a truism called Bergmann's rule holds that animals are smaller in hot climates and bigger in cold climates. Think about wooly mammoths versus Madagascan tenrecs. But a debate persists about why this is so, and whether it's because of temperature itself or because of indirect results, like food abundance and conservation of heat energy. Ross Secord and colleagues set out to answer this question by studying horses from now and in the past.
About 56 million years ago, the Earth warmed up during a phase known as the Paleocene-Eocene Thermal Maximum, or PETM. Carbon dioxide increased and global average temperatures rose by about 5 to 10 degrees Celsius. At least in horses, body sizes went down as temperature went up.
The little horse in the picture above is called Sifrhippus sandrae, and he is the earliest known horse. The species probably came to North America and Europe from a high-latitude land bridge that opened during the warming phase. After its arrival, its body size shrank by 30 percent over the next 130,000 years, Secord and colleagues say.
They considered the dryness of environments, atmospheric pressure and even the nutritional content of plants exposed to higher levels of carbon dioxide, and ultimately conclude that temperature was the primary driver of size evolution in Sifrhippus. Their paper appears today in Science.
So does this mean that global warming will make us all smaller? Taken to its furthest extent, this hypothesis sounds like some sort of Malthusian dream. Smaller humans would likely require less food. That means we would require less land on which to grow the food. Then we would use less fertilizer, and we'd need fewer factories to make fewer tractors to plow the fields on which we harvest the smaller amounts of food. Fewer factories=less energy requirements=fewer carbon dioxide emissions=less global warming?
Sound crazy? Maybe, but I'm not the first person to say this. Philip Gingerich, a researcher at the University of Michigan who first noticed decreasing body size during the PETM, said he jokes about this all the time.
"We're going to be walking around 3 feet tall if we keep going the way we're going," he said. "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."
Like NASA's new cloud-cooling study, this vision of the future is an almost poetic example of nature taking its course in spite of us. Things really do want to even out in the end.
I thought the correct term was climate change, not global warming? That way any change in the climate can be framed as part of the problem.
What is it with you people?You act like global warming is a religion or something.People either screaming its true and we are going to feel the effects of 32ft waves,i live in florida,or people screaming it isn't.Call it what you want global heating,earth warming,whatever.The fact of the matter is earth is getting warmer.
No,it isn't exactly climate change.While you CAN refer to it as climate change the real term is global warming because the earth(globe)is getting hotter(warming). climate change refers to the basic change in climate which could just as easily mean global cooling.
I find the idea of shrinking people ridiculus. The proof for animals that CAN'T manipluate their enviroment show that mammels shrink.We humans on the other side will keep being 5-6ft tall because we will be living in airconditioned houses,workplaces,ect.
I'm willing to believe this. After all- it's rather evident by simple observation- look at the average heights amongst peoples of warmer climes; Chinese, Mexicans, Hawaiians, Filipinos, Kiwis, etc in contrast to peoples like Russians and Nordics.
Probably a secondary effect; the climates effect upon which kinds of vegetation and livestock are available, which in turn affects the prescribed diet of a region, and finally- growth.
@marcoreid: it is. especially since only the first part of the cycle is actually global WARMING. the next part is an ice age; definitely not warm.
still, there are more side effects to global warming, or global climate change, if you will. (or if won't. that seems to be acceptable as well) the most potentially dangerous one being the ice age, so it would be preferable, weather the climate change is caused by humans or not, to slow, or even halt it's progress. just my 2 cents, though.
why learn from your own mistakes, when you could learn from the mistakes of others?
“The most incomprehensible thing about the universe is that it is comprehensible” -Albert Ein
You can't be serious. I guess dinosaurs are now the size of lizards because of Global Warming. I fully expected you to tie in the increasing salt content of the oceans and the moon getting further from the earth as causes of the shrinking. I even expected you to end with "Global Warming is caused by those evil oil men and we will all get shorter if we pump gas in the heat."
In truth, there were many factors that could have caused a size change. The early animal forged on fruits and foilage and the present animal has switched to grasses. Grass may be harder to digest but it is much more abundant than fruits and foilage. Another possible explanation for increased size is the domestication of horses. Runts were removed from the herd allowing the stronger working horse to survive.
I have to close by saying the world may be getting warmer but I have not gotten any smaller(I am fat). Global warming is increasing the food supply and I am guilty of eating too much of it.
Global Warming is an effect of Climate change. It is still the proper term, it is similar to driving. You can go forward or backwards but you are still driving. So It can mean either Global Warming or Global Cooling.
If you want to go more in depth it shouldn't be called Global Warming at all because Global Warming is technically caused by the Green House Effect. The Green House Effect is not causing Climate Change as it is something that has existed since, nearly, the creation of the Earth. It is a necessity for the planet to sustain life and maintain a habitable temperature (59 degrees Fahrenheit). So it should be called Climate Change even if the planet is warming.
I also find it hard to believe that temperature alone has this great of an affect on body size. Many animals throughout the history of the Earth have been much larger and much smaller than they are now. Looking at our own human evolution, we have only grown in stature rather than shrink. If anything I think that the amount of oxygen and carbon dioxide in the air would affect body size in combination with temperature. The CO2 because it would increase the nutrients required for plants to thrive therefore creating more food and oxygen for the planet.
Actually, they're not saying that dinosaurs should have been smaller. Cos, y'know, dinosaurs were reptiles, not mammals... Or did you not read the article? Or the headline? -.-
Strange the largest animals to roam the planet were alive during a period of time when the air was much warmer. They were called dinosaurs.
This 'school of thought' failed to consider the following:
1. CO2 has a half-life (T1/2)of 100 years. In five T1/2s, anthropogenic CO2 will be effectively gone.
2. We only have around 2-3 centuries of fossil fuels, in all forms, left.
3. Even if CO2 continues to climb for the next 300 years, it will be gone during the following 700 years.
Conclusion: Regardless of how much CO2 we spew into the atmosphere, it will all be gone before the next millennium begins, leaving just other mass nonhuman extinction and a re-cooling planet in its wake. This is not enough time to radically change a genome (except bacteria, etc) via evolutionary forces. The only genome changes will be from eradicating some of them via natural deselection.
CO2 has a half life of 100 years? Can you cite a reference on that? Also what does it break down into?
CO2, with an enthalpy of formation of -393.51 kJ/mol, is one of the most stable gas molecules around. For comparison, water in a vapor form has an enthalpy of formation of
-241.82kJ/mol. Even when water is in a liquid form its enthalpy of formation is -285.83 kJ/mol...which is still not as stable as CO2 in the gas form.
Half life implies instability and that the molecule or atom will spontaneously…and that is the important point, spontaneously…change into something else. The term is mostly applied to radioactive elements or substances with a positive enthalpy of formation.
I can think of some reactions that can happen with CO2 that can produce a product with a lower enthalpy of formation. But that is not a spontaneous breakdown of the CO2 itself…there has to be other reactants present.
This makes little sense the current largest land animals are generally along the equator in warm/hot climates elephant etc
and did'nt the mammals survive the ice age as a result of diminutive size?
and in relation to the size of humans diet is the largest contributor to size as demonstrated when western diets are popularised case in point being Japan I remember news reports of Japanese kids growing taller than average as a result burgers and fast food being introduced into their diets
there might be another reason animals were so much larger in the age of the dinosaurs, bare with me here but the moon was closer to the earth and has been moving away from us over millions of years and we are directly affected by it's gravitational pull so do'es it not make sense that millions of years ago the effect of gravity on earth were weaker therefore animals could grow much larger?
and as we see today the largest animals in existance are supported in growth by their environment (bouyancy) whales etc,
im not one to be grammar police.. but the word "littler"? really?? you work for popsci, atleast have someone proof read it....
Anyway.. although i didnt read ALLLL the comments.. i thought our size was directly related to the amount of Oxygen not heat... when the dino's were alive it was definitely a warmer period but richer in oxygen.. just like bacteria grow in oxygen, why wouldnt it apply to humans? we might be shrinking but not due to heat..IMO
If warming, in this case suggested as "global warming", was a cause of the "shrinkage" of animals, citing the horse in this case, then consider this fact. Warming would have been worldwide, and if so, how do you explaing evidence that horses grew larger in other countries outside of the North American continent? Specific species may vary and their survival is much more complex than presented in the simple "global warming" theory. Thus, the "evidence" of causes of this shrinkage is very premature and does not comply with accepted scientific conclusions. Note also that about any attempts to link anything to global warming is readily published by the media, perhaps because they have bought into this theory, and their biased liberalism promoting the philosophy that the only cure is one world control of governments. This has become the new popular "buzz word" and presented without much, and often times without any, bona fide scientific evidence. So, you scientists get back to your research and do it properly this time. Further, you should stop with the fanatical, perhaps even religious, belief that everything is linked to or caused by "global warming". Monty Weddell Dallas, TX
In my Historical Geology class, my teacher taught that levels of oxygen in the atmosphere played a significant role in the size of life during that period of time. I feel like this does not relate to this story but is more closely related with the size of dinosaurs when the levels of oxygen were around 20%.
I was under the understanding that size back then had to do with oxygen levels as well. Especially insects, if I remember right. I would be willing to bet that mammallian size isn't as affected by the temperature as the study may lead. A greater look at all species, in all regions, would need to be done to satisfy that theory. As mentioned by others, you can't just pin point one species and say it equates to all. Each species has different growth patterns. On top of that, there may have been local factors that may have driven size. Food abundance (not related to global temps), local predators, competition with other species and probably more that I'm forgetting all play a role in the size of a species.
Interesting idea. Gingerich is right about one thing: "You can either adapt, or you go extinct, or you can move...." He's wrong about the other, though: "...there's not a lot of place to move anymore."
Have you taken a flight across the U.S. lately? Or England? Or Europe? Or southeast Asia? Or a drive across the river to New Jersey? Most of the habitable land on earth is very lightly populated. Earth's human population is increasingly migrating to cities because large cities offer many more economic opportunities than rural villages.
Now if you're worried about coastline cities that may end up under several inches of water by century's end if you believe the computer models...well, they'll either build levees and dikes (like the Netherlands) or people will move (like New Orleans). Humans aren't innately stupid. They adapt; a fact lost on most Global Warming alarmists.
P.S. They call New Jersey the Garden State for a reason. Even though it's the most densely populated state in the U.S., there are farms, fields, and forests everywhere separating the hundreds of small towns. Only a relatively small portion of the state is densely populated. Pay a visit. It's beautiful in the spring.
High temperatures probably had little to do with the reduced size of mammals during this period. The most likely cause was the increase in surface gravitation at that time. This is explained at www.dinoextinct.com, click on 'The Gravity Theory of Mass Extinction' to view a PDF summary of the theory.
The largest dinosaurs of the Mesozoic, the sauropods, existed primarily in near-equatorial regions of Pangea where temperatures were higher than they are today.
@ matsci1: CO2 is changed into cellulose, and similar compounds by photons facilitated by chlorophyll. Oxygen is released in the process.
In natural systems, be it the carbon cycle or in dosing a drug, this is how 'half-lives' is used. It need not be 'spontaneous'.
I thought size was due to oxygen levels too. But it might be heat as well. Maybe they are dependent somehow. I have no expertise on this subject so i'm just thinking out loud...
The reaction you described is photosynthesis.
There are also other carbon sinks that absorb CO2 from the atmosphere... to name a few, Marine organisms, snails and eggshells are composed of calcium carbonate, CaCO3.
Ecosystem chemistry is very dynamic and there are a lot of factors to consider
I am not debating that there are reactions that remove CO2 from the atmosphere. However I would like to read the reference that says that the “half life” for CO2 in the atmosphere is, as you have listed it, 100 years.