Just a thought to add to this:
Take the cicada. Some forms of this insect hide in the ground for 17
years before emerging into the forest, where they breed, lay eggs and
die after six weeks. Scientists believe that the cicada has a predator
that also emerges periodically.
“If the cicada came up every nine years and the predator came
every six years, the cicada would be killed off after 18 years. If the
cicada came up every seven years, it would take 42 years before it was
killed. By emerging after 17 years, a prime number, it keeps out of
step with the predator for longer. That’s the beauty of prime numbers,”
Professor du Sautoy said.
The way that story is told, isn’t it getting causality the wrong way around? Our assumption is, rather, that there were indeed cicadas that came up at 6, 7, 8 and 12 years, and did get eaten by the predators. Only those coming up on the 17 year cycle survived down the generations?
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