Posted on 08/11/2005 11:02:22 AM PDT by ZULU
Humans are likely responsible for the extinction of Ice Age megafauna—large mammals like giant sloths, short-faced bears, mammoths, and saber-toothed cats—that occurred in the Americas around 11,000 years ago, a new study says.
Scientists have long debated whether giant pre-historic mammals disappeared because of climate change or because humans hunted them to extinction.
The mass extinctions coincided with both the end of the last Ice Age and the arrival of humans in the Americas around 11,000 years ago. This timing has made it difficult for scientists to isolate the cause of the species' disappearance.
But a study comparing the extinction of giant ground sloths in North and South America with the disappearance of their smaller relatives in West Indian islands has helped clear up the picture, scientists say.
The researchers say archaeological and fossil evidence strongly suggests that ancient hunters pushed the animals to extinction.
Giant ground sloths "cruised through" at least 22 major climate cycles as the continental ice sheets in North America advanced and retreated over the last two million years, said David Steadman, a paleobiologist at the University of Florida.
Steadman is a co-author of the new study published in the Proceedings of the National Academy of Sciences.
"The only thing that's different [at the end of the Ice Age] is the arrival of people," he said.
Giant Sloth: A Case Study
Until about 11,000 years ago, at least 19 different sloth species lived in North and South America in a variety of ecosystems. Only a few small, tree-dwelling sloth species survive today.
Steadman and his colleagues argue that if ecosystem shifts resulting from climate change caused the sloths' demise, then all extinctions—on both islands and the mainland—should have taken place at the same time, as the last Ice Age ended between 15,000 to 9,000 years ago.
Radiocarbon dates of bones, dung, and other tissue of extinct sloths place their last appearance in North America at around 11,000 years ago and at about 10,500 years ago in South America, Steadman says.
But on the islands of Cuba and Hispaniola—shared today by modern-day Haiti and the Dominican Republic—sloths survived until about 4,400 years ago.
Their subsequent extinction coincided exactly with the arrival of the first humans on the islands, Steadman says.
"What [this study] shows us is that there's this great big suggestive pattern that we find: Wherever human beings first appear all around the world, these large mammals pretty quickly become extinct," said Gary Haynes, an archaeologist at the University of Nevada at Reno, who was not involved in the study.
"[Some] people will say that you have to [establish the cause of extinction] species by species, and I think they're probably right," Haynes added. "But the study does create a good model that might make us think that if it worked for one big animal it's probably what we'll find for other big animals."
Overkill Vs. Climate Change
Steadman and his colleagues argue that megafauna species on the American continents, having evolved in an environment without humans, may have been particularly vulnerable to the sudden appearance of big game hunters.
The 5,000-pound (2,300-kilogram) giant ground sloth is a case in point. In addition to having no fear of humans, it was the size of a modern-day elephant, it couldn't hide, and as it name implies, it moved very slowly.
"Walking up to a ground sloth and trying to spear it to death probably wasn't one of the most macho things they [early hunters] did," Steadman said. "Any hunter could outrun one."
But other scientists maintain that climate change was the driving force in Ice Age extinctions. They argue that the retreat of ice sheets from North America caused a major change in habitat that the giant mammals couldn't adapt to.
At the peak of the Ice Age around 20,000 years ago, the ice covered much of North America.
As the sheets melted between 18,000 and 8,000 years ago, warmer temperatures and shifting rainfall patterns forced plants and animals to move out of old habitats and into new ones.
Proponents of the climate-change theory add that there's little evidence that humans hunted anything other than mammoths. Yet species like wild horses, camels, and saber-toothed cats all went extinct at about the same time.
"There are no archaeological sites for species other than mammoths, and perhaps mastodons, where you find a spear sticking out of an animal, and everyone agrees that there is evidence of human hunting," Nevada's Haynes said.
"So the lack of kill sites doesn't bother me," he added. "There's a real lack of a 'smoking gun' implicating either climate change or human hunting, but that's true for every theory."
Climate change may have been a factor in pushing the animals to extinction, Steadman says, but it took humans to push them over the edge.
"Animals like the ground sloth, which had a poor ability to regulate body temperature, should have thrived in a warmer climate," he said.
No, sorry. Try reading for comprehension next time.
Very logical.
It is logical when you understand it.
When you don't, though, it's easier to just to ridicule things to cover your discomfort over your inability to grasp the material.
What is not a theory is that scientists have too much time on their hands coming up with more and more theories. Until they present facts their theories belong in comic books.
What also isn't in question is that you obviously have no real idea how science works, or why scientists propose as many plausible hypotheses as they can think of, and then continue to perform validation/falsification tests on them as long as it takes for the results to clearly indicate which explanation is the correct one (or closest to the correct one, anyway).
My high school had 2000 students. To think that at one point, there were 5 of my high schools throughout the world is just incomprehensible.
Yes, it is amazing how effective the scientific method is at separating valid ideas from horse manure.
They make pronouncements on theories they pull out of their @sses and call it good science,
No they don't. You might want to refrain from trying to critique a field you don't know enough about to properly review.
but let someone suggest that there could be a higher power involved in creating the universe and they insist that is 'not scientific'
The "suggestion" is indeed not scientific, and neither is any other "suggestion" of any other sort on any other topic. If you ever get to the point where you have a testable *theory* on that subject (*and* know what actually constitutes a theory in the scientific sense and what features your proposal will have to have to qualify), do feel free to get back to us.
and thus not worth teaching against their other holy theory of 'evolution'.
Not in science class, anyway. Go right ahead and propose Odin or Shiva or whoever in a class on religion or sociology or history if you wish.
I guess 'good science' is whatever they pronounce it to be.
I guess you don't have a clue about this subject, but you keep talking anyway. "Good science" is that which follows proper scientific procedure and validation methods. If you choose to just "propose" something instead but not go through the hard work necessary to demonstrate the validity of your proposal via the proper methods, then you shouldn't complain when your proposal doesn't qualify as science, or appropriate for teaching in science class.
"...why scientists propose as many plausible hypotheses as they can think of, and then continue to perform validation/falsification tests on them as long as it takes for the results to clearly indicate which explanation is the correct one (or closest to the correct one, anyway)."
Even you admit they are guessing!!!
The problem with the scientific community today is many have politicized the process of validation of their ideas. They present some of the most convoluted/ridiculous theories as FACT instead of the educated guesses they truly are (I use the term educated loosely here). I have nothing against the scientific method properly and honestly applied to test hypotheses and I do believe there are many researchers who are honest, but there are many who are only reporting/validating the person paying them to do their research.
OTH, YOU respond with personal attacks against those here who have contempt for these would be Einsteins. Pehaps your feelings are hurt by the low opinion some of us hold for these scientific parasites spewing their garbage. My comments were and are not meant personally to you, only to the subject at hand. You have absolutely no idea as to the level of my education and/or experience. The fact I criticize the scientific community does not make me any less intelligent than you sir/madam.
"It's mainly people starting with a conclusion, and looking for evidence to support it, and trying to ignore or minimize evidence that contradicts it.
In the end there's nothing useful to learn from their theory, other than that they have an agenda."
Exactly.
Admit it. It is all personal opinion.
And how many years and federal dollars did it take for this enlightening research. Am I,as a taxpayer,getting my monies worth? duh!
Animals will one day sue humans.
You wouldn't happen to know this guy?
Please don't ask me to explain anything about this strip, such as how the shark and turtle are talking, how the shark is holding the spear gun, where he got the spear gun, etc. Just know that I saw this on the web site for the strip (www.slagoon.com) and knew that I was hooked.
Sorry. Not even a sloth bone.
Now if we could just be responsible for the extinction of liberals we'd be gettin somewhere....
Oh, please ... just, frickin' please.
Sorry. Begging will get you nowhere.
No sloth or Mammoth for you today!
Obviously they would have preferred the humans to starve instead.
Must be a great feeling, going through life filled with such self-loathing for fulfilling Holy Darwin's Sacred Dictate:
"The fittest shalt survivest; yea, he shalt extinctify the unfit competitor."
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The footprint was headed towards the Rio Grande.
Well yeah, I'd be heading for the water too if I just stepped in some lava! LOL
So you're saying science is just one "shot in the dark" after another, or put another way, "A bunch of wild-ass guesses" (SWAG)?
"Science" today has been prostituted by the left to be just another hammer to force their warped view of the world on the rest of us politically. Just as one doesn't need to be a meteorologist to know when it's going to rain, you don't need to be a "scientist" to smell the BS.
You left out "peer review". They produce theories that their "peers" agree with. It is not only their opinion it is the opinion of elitists that that won't see the light of day unless it has their stamp of approval on it. It's called "The scientific establishment" and to get along you better toe the line of the elitists. To suggest that I don't see the big picture is pure bunk. I spent three hours in a public meeting last night listening to environmentalist poppycock. I know what the big picture looks like and it leaves out a whole bunch of people that have common sense.
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