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“One can spend all day finding out things one never needed to know”

01 June 2020, at 7:53am

The elderly Labrador owned by my equally elderly next-door neighbour is slowing down with arthritis, despite NSAIDs and glucosamine together with a wonderful mix (his words not mine) of devil’s claw tuber, sarsaparilla root and Boswellia gum. Thank goodness he didn’t ask for my professional opinion on his canine friend’s medication. Instead, at the required two metres distance, we talked about slowing down more generally.

For ages we young-uns (again, his words not mine!) have been told, in the words of the Simon and Garfunkel song, to “slow down – you move too fast”. And now the queue at the supermarket makes us slow down, doesn’t it? That or developing arthritis… or being a tortoise! I suggested to my elderly friend that while a mouse lives for a year or two, a dog for 10 or 15, the slow old tortoise can reach seventy for sure.

Is it being ectothermic that leads to this extended longevity, I wondered? I say ectothermic rather than cold-blooded as a Gopherus agassizii tortoise living in the Mojave Desert has to cope with temperatures of around 50 degrees and can live to up to 80 years. Their heart rate, though, is around 10 beats per minute. Not a piece of information I have immediately to hand it must be said – but the joy of Google Scholar is that within an internet instant I can access a great thesis like that of Ann Bowles 20 years ago on “the effects of flight noise from jet aircraft and sonic booms on hearing, behaviour, heart rate and oxygen consumption of desert tortoises”.

Honestly the only problem with having such a plethora of information at the tap of a button is that one can spend all day finding out things one never needed to know at the beginning of a literature search for something completely different. But perhaps that’s the whole point of slowing down – not worrying that you spent half an hour reading a paper packed full of fascinating facts you will never in all probability ever need to know.

Take the concept of physiological time for instance. Body size dictates your lifespan. Your metabolic rate as a species scales with your body mass to the 0.75. We know the importance of that allometry in giving toxic drugs such as chemotherapeutics. And it links with lifespan as well. The mouse lives a shorter time than the cat, quite apart from whether one is eaten by the other or not! And the elephant lives longer than the cat, that goes without saying.

A plot of the number of heartbeats per lifetime against body weight and life expectancy gives a remarkably constant number – around seven and a half hundred million heart beats per lifetime – please don’t start counting! Or at least that’s what Herbert Levine calculated in a paper in the Journal of the American College of Cardiologists back in 1997 and I’m afraid life’s too short to go back over his maths and see if I agree with them.

Except… what about birds? A budgie is the weight of a mouse but can live for 15 years while the mouse lasts at most until it is three. The average heart rate for both is 300 to 600 beats per minute, so why is their lifespan so different?

The naked mole rat is the same size as a mouse and yet living for 30 years with next to no neoplasia noted and existing at oxygen levels giving a hypoxia that would kill us. Not much of a life though, you might say – they live in a eusocial group where sterile males do the bidding of the giant queen weighing in at 70 grams, taking orders through chemicals in her urine. And when she dies the remaining females who fancy taking over fight to the death for the place at the top. And you thought that we live in a crazy world at the moment – think again!

Associate Lecturer, Veterinary Ophthalmology at St John's College, University of Cambridge

David Williams, MA, VetMB, PhD, CertVOphthal, CertWEL, FHEA, FRCVS, graduated from Cambridge in 1988 and has worked in veterinary ophthalmology at the Animal Health Trust. He gained his Certificate in Veterinary Ophthalmology before undertaking a PhD at the RVC. David now teaches at St John’s College, Cambridge.

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