Monday, August 28, 2006

Climate Change or Overkill?

The end of the Ice Age brought about a lot of extinctions among the large mammals. The different species of oversized hairy things dropped from all over the globe. The two places that were hardest hit were the continents of North America and Australia. These places lost the largest percentage wise number of large mammals. Some of the more famous are the various species of mammoth (woolly especially remebered), several species of horses, rhinoceros, giant slothes, sabre toothed tigers, and much more for North America. For Australia wombats the size of rhinos and kangaroos that could look giraffes in the eyes - or near enough - dropped off the shield of that continent. South America lost some. Asia and Europe lost less. Africa lost least of all. There are two competing theories about that. The first and predominant is that the climate changed so drastically that none of those animals could adapt to the changes. They died out. End of story. The second theory is that the arrival of man or a technolithic toolkit was the cause. There are pro's and cons to either theory. Neither one is pretty solid, honestly.

The human overkill hypothesis has some strong data in favor of in in the historical record. The ravages that mankind has done to various places as they've shown up has been pretty drastic. Let's take the example of the Maori and what they'd done to the avian fauna of New Zealand. The most famous of those is, of course, the Moa. There is also the arrival of mankind on Madagascar too. The giant lemurs and giant birds went poof too. It's not hard to believe that mankind's arrival in North America could cause those extinctions at the end of the Pleistocene there too. Here's the rub. Mankind didn't arrive in NorAm at exactly the right time for that to happen as originally was thought: some very good evidence predates the previous times that they thought people came to North America. That puts a small damper on things, unless you believe it took a technological breakthrough for that to happen. Like, oh say, those damn Clovis people. Not you, Jeromy, if you actually bother to read this. The timing of arrival in Australia is spot on though for the extinctions. I chose the Maori and Madascarans for the reason that they are not Western societies because some people have this view that it is only the West - or its influence - that is environmentally destructive. Yes, it can be. However, as I've quoted before from Hallam's works:
The sombre picture outlined above should dispel once and for all the romantic idea of the superior ecological wisdom of nonWestern and pre-colonial societies. The notion of the noble savage living in harmony with Nature should be despatched to the realm of mythology where it belongs. Human beings have never lived in harmony with nature.
I think that you can see that I am disposed to this hypothesis. Pielou's work states there are issues here, to be sure.

Recently, there has been a lot of different works from the environmental/climate theory camp. They have made me doubt just a tad my previous leanings, but not completely shaken me from it. Most recently there was a study on what killed off the megafauna of Australia. There was also a study on what killed off the mammoths in NorAm. It's not persuasive, but suggestive. After all, massive climate change, lots of dead animals that can't adapt. ok. Makes sense.

However, waitaminute! Why are there a lot more dead animals elsewhere? Well, there are some. However, the extinctions in Asia and Europe were less. In Africa much less. The Overkill Hyopthesis suggests that is because those areas had more humans for longer and animals had a chance to adapt (Africa being the longest and 'suffered' the least). Pielou points out that the problem with the climate change theory is that there are lots of very species specific explanations, but nothing blanket covering. However on the other hand, he also states that the climate of ice ages was radically different than even that of spots on earth that have glaciers now. It doesn't have much of a parallel with the modern world climate wise, so it could be the change really was really big. yet...

Why did the giant bison go extinct and not the smaller ones? Or why did the mammoths get wiped out? There are several possibilities and permutations on this question. However, the climate change theory is the reigning one among paleontologists, so don't be fooled by my skepticism. I Am Not A Paleontologist. I am just enjoying reading about it and have since I was a young boy. I'm also a part-time blogger that likes to talk about the things that he likes to read, so go read about it too. ;)


Nick E. said...

Here's a persuasive argument for overkill:

Will Baird said...

Thanx, Nick!

When I have a little more time, I'll read it. I just glanced through it now and it looks at least investigating.