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Megafauna Extinction Due to Climate
jvchamary writes "Most biologists believe that Earth is currently undergoing its sixth mass extinction. The cause? Human activity, either directly (e.g. the Dodo) or indirectly (e.g. the Amazon rainforests). The disappearance 30,000-45,000 years ago of the Australian megafauna, large animals such as the marsupial lion, is often attributed to hunting by Aboriginal settlers. However, recent research in Proceedings of the National Academy of Sciences suggests that it was more likely a shift in climate, rather than hunting, that caused the over-sized organisms to die-out (via Nature and the BBC)."
Hmm. I know a relatively famous (in his field, at least) paleoanthropologist,and was just talking to him about this very thing. I asked him his thoughts about the two competing theories of large animal extinction.
He said that while it was currently fashionable to blame the climate and exonerate aboriginal hunters, he said it makes perfect sense that it was probably a combination of the two.
We modern humans have a definite tendency to underestimate the intelligence, resourcefulness and persistence of our forebears. A good example of this is all the mysticism and voodoo crackpot theories of how Stonehenge, the pyramids, etc. were built. The fact is that ancient people were quite -- sometimes ingeniously -- resourceful at accomplishing what they wanted to do.
Along that same vein, I have no doubt that they became quite expert at killing such things as mammoths, which would feed a whole clan for months (esp. if you dry some of the meat, etc) and provide ivory, bone and fur besides. Mammoth hunting would also have been a great opportunity for clan members to show their skills, bravery and dedication to the tribe -- something of great importance in many aboriginal societies.
Paleoanthropologists are a pretty interesting bunch to talk to.
- Alaska Jack
Don't give it up so quickly. There are some huge problems with the "climate-only" theory. Namely
A) In most of the world (even if not for some animals in Australia) extinctions were timed, as well as we can measure, with the arrival of humans into each region, even though the global climate was changing as a whole
B) Species survived far more dramatic climate changes in the past, with nowhere even approaching the degree of megafauna losses. The scale of megafauna losses last ice age was staggering - for the largest animals, often over 90% of species.
C) We've seen this occurring in more modern times. For example, the Moa of New Zealand; there is essentially no doubt that they were butchered by the Maori, because their fossilized cooking pits are filled with Moa remains in nice neat layers - huge numbers of them that the species clearly couldn't have sustained. When the Maori were discovered, they talked about hunting and killing them. There's a sudden cutoff point in Maori sites in which suddenly Moas disappear from the diet.
Also, climate change isn't the only alternative theory. There's also the concept of humans being a carrier for diseases/pests, human-induced environmental changes, human killing of "keystone" species, and my favorite, "many of the above combined".
Aeris Died For Your Sins.
That's not quite accurate. The "little ice age" lasted from 1450 to 1820, a time during which there were sunspot highs and lows. The lows of 1645-1715 (the Maunder minimum) and 1795-1820 (the Dalton minimum) just happened to be the coldest points of it. Some of their other minimum numbers seem a bit odd, too.
The whole "sunspots affecting temperature to the degree we're seeing recently" thing has always been rather suspect. It's not going to affect directly - radiant energy varies by only 0.1-0.2%. But perhaps indirect effects might be occurring, and some have been suggested (such as through altering ozone levels). Nonetheless, the best-predicting climate models currently show that the most important role is played by humans.
Aeris Died For Your Sins.
In 10 million years, perhaps all primary terrestrial life will be descendents of Homo Sapiens. Perhaps we are just in the process of a morphological gene renormalization.
We will have human-derivitive predators, human-derivative herbavores, human-derivitive sea mammals, etc..
Sound strange? It shouldn't. Every once in a while, a specific set of genes shows so much ability to dominate that it completely overwhelm all others and then slowly specializes in the ecosystem, taking on the familiar roles we see. The first Dinosaurs were all morphologically identical with differentiation only occuring as the other species in the ecosystem were driven to extinction and leaving room for the different ecological niches to be filled through evolved Dinosaur morphology. Same with Mammals.
I suppose this vision could require a collapse of civilization such that humans actually had to fill all the various niches in the ecosystem, but given 10 million years, I'd say that is pretty likely. It would be pretty gruesome in the beginning, with canabilism and whatnot being fairly common, but after a few hundred millenia it should shake out to a variety of different predators and prey subspecies quite readily.
The reason that it can be true that 1+1 > 2 is that very peculiar nonzero value of the + operator