Saturday, July 9, 2005

Humans and extinction of other species

Humans causing extinction of other species is apparently not a new phenomenon. But I suppose the experience of the Sabre Tooth Tiger and Woolly Mammoth's in North America might demonstrate that. Or, was that human-caused because in Siberia they've found tremendous numbers of Woolly Mammoth's frozen in the ice with fresh daisy's in their stomach. As if they were flash frozen.

In any case ...

'Fires wiped out' ancient mammals (By Helen Briggs, BBC News science reporter)

We have an article discussing what happened after humans arrived in Australia. At least in Australia there's less doubt of how people arrived there - they arrived by sea from Indonesia around 50,000 years ago. This seems like a very obvious and likely story, with much less doubt than the accepted story of humans arriving in North America.

The article goes over research that shows at 50,000 years ago the diet of certain Australian birds changed drastically from grass seeds to material from scrub-brush. The birds that were able to change their diet (the "opportunistic feeders") survived while the others (the "picky eaters") died off. Their evidence is the quality of the carbon in egg-shells.

The cause they point to is that humans set fire, for a number of reasons, to the landscape as they arrived. e.g. it was a hunting technique (to set fire to the brush to flush out the animals), a farming technique (to clear the land), or merely to signal others. The fires killed off the plants that were in the landscape, changing the mix of plants quickly and drastically. Much too fast for evolution to handle the change, and as already discussed the scientists believe this led to mass extinctions in Australia.

This story connects with a prior one: Major species extinction periods

That story discussed how scientists have mapped out the previous periods of mass extinction, and determined each one happened due to external influence (that is, a major meteor strike on the planet invoking drastic climate change).

The scientists are seeing growing evidence that we are in a new period of mass extinction, but this time it's caused by human influence.