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Mammalian species seem to have a fixed time on our planet, enjoying about 2.5 million years before they go extinct. A study of 22 million years and a detailed sequence of rodent fossils indicates that species appear and disappear in pulses at regular intervals (Nature 2006;443:687-91). In a new twist to an old tale, the duration and timing of such periods correspond to that of variations in the distance between the Earth and the Sun and the tilt of the Earth's axis-factors thought to be responsible for long term climate cycles. In other words, species remain stable until climate change triggers rapid bursts of extinction and speciation. That we've been here only 250 000 years somehow fails to provide comfort.
Ever heard of “protein trafficking?” If you haven't, go back to your biochemistry textbooks now. Each cell contains