Skip to main content

Why prime numbers matter

The website has been sent for review a book called Shapes by Philip Ball. It's an interesting book about shapes in nature - everything from why shells have a particular form to why a zebra's pattern looks like it does. Something the reviewer drew to my attention, was a fascinating observation about a creature for whom the idea of prime numbers isn't just a bit of abstract maths, but a matter of life and death.

Apparently there are some cicacada species whose life cycle tends to operate on prime numbers - say a 13 year or 17 year period. Most of their life they are tucked away safe underground, but once every 13 or 17 years they pop up to breed and are vulnerable. It has been suggested this is a self preservation thing. Typically the number of predators around go through regular peaks. Imagine your life cycle was 12 years rather than 13. Then you'd be particularly susceptible to predators with a 2, 3, 4 or 6 year peak, if that peak synchronized with your cycle. But with a prime number life cycle, a predator is much less likely to be able to synchronize.

As it happens, these cicacadas don't have any predators with appropriate cycles. But it has been suggested this is because said predators have died off/given up and moved to the South of France/etc. due to limited prey.

The only problem I have with this theory is that I'd expect it be more common than it seems to be... but I still love the idea that a species' existence could depend on prime numbers.


  1. Yes, I saw this on Planet Earth. Quite fascinating. Ain't evolution a remarkable and beautiful thing?


Post a Comment

Popular posts from this blog

Is 5x3 the same as 3x5?

The Internet has gone mildly bonkers over a child in America who was marked down in a test because when asked to work out 5x3 by repeated addition he/she used 5+5+5 instead of 3+3+3+3+3. Those who support the teacher say that 5x3 means 'five lots of 3' where the complainants say that 'times' is commutative (reversible) so the distinction is meaningless as 5x3 and 3x5 are indistinguishable. It's certainly true that not all mathematical operations are commutative. I think we are all comfortable that 5-3 is not the same as 3-5.  However. This not true of multiplication (of numbers). And so if there is to be any distinction, it has to be in the use of English to interpret the 'x' sign. Unfortunately, even here there is no logical way of coming up with a definitive answer. I suspect most primary school teachers would expands 'times' as 'lots of' as mentioned above. So we get 5 x 3 as '5 lots of 3'. Unfortunately that only wor

Why I hate opera

If I'm honest, the title of this post is an exaggeration to make a point. I don't really hate opera. There are a couple of operas - notably Monteverdi's Incoranazione di Poppea and Purcell's Dido & Aeneas - that I quite like. But what I do find truly sickening is the reverence with which opera is treated, as if it were some particularly great art form. Nowhere was this more obvious than in ITV's recent gut-wrenchingly awful series Pop Star to Opera Star , where the likes of Alan Tichmarsh treated the real opera singers as if they were fragile pieces on Antiques Roadshow, and the music as if it were a gift of the gods. In my opinion - and I know not everyone agrees - opera is: Mediocre music Melodramatic plots Amateurishly hammy acting A forced and unpleasant singing style Ridiculously over-supported by public funds I won't even bother to go into any detail on the plots and the acting - this is just self-evident. But the other aspects need some ex

Which idiot came up with percentage-based gradient signs

Rant warning: the contents of this post could sound like something produced by UKIP. I wish to make it clear that I do not in any way support or endorse that political party. In fact it gives me the creeps. Once upon a time, the signs for a steep hill on British roads displayed the gradient in a simple, easy-to-understand form. If the hill went up, say, one yard for every three yards forward it said '1 in 3'. Then some bureaucrat came along and decided that it would be a good idea to state the slope as a percentage. So now the sign for (say) a 1 in 10 slope says 10% (I think). That 'I think' is because the percentage-based slope is so unnatural. There are two ways we conventionally measure slopes. Either on X/Y coordiates (as in 1 in 4) or using degrees - say at a 15° angle. We don't measure them in percentages. It's easy to visualize a 1 in 3 slope, or a 30 degree angle. Much less obvious what a 33.333 recurring percent slope is. And what's a 100% slope