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Sunday, 6 May 2012

Haldane picks on something his own size

This review featured in the Guardian this week, http://www.guardian.co.uk/science/2012/apr/27/possible-worlds-other-essays-haldane-review, about the pithy, eccentric but brilliant JBS Haldane, reminded me of some reading I did last year about him. This is Haldane Jnr by the way, (1894 to 1964), the British geneticist and evolutionary biologist, not the physiologist who is occasionally referred to in Sports Science degrees, certainly in physiology education, a firm favourite of PhD examiners, ("what is the Haldane transformation? Answered by either "er dunno" or "The multiplication of inspired oxygen concentration by the ratio of expired to inspired nitrogen concentrations in the calculation of oxygen consumption or respiratory quotient by the open circuit method, I think") and more highly revered for his invention of the first gas mask in WW1. JBS Haldane was John Scott Haldane's son (and subject of much gineau pigging by his father) and was the author of some quite majestic pieces of scientific writing, here are a few to inspire;

"To turn to zoology, suppose that a gazelle, a graceful little creature with long thin legs, is to become large, it will break its bones unless it does one of two things. It may make its legs short and thick, like the rhinoceros, so that every pound of weight has still about the same area of bone to support it. Or it can compress its body and stretch out its legs obliquely to gain stability, like the giraffe. I mention these two beasts because they happen to belong to the same order as the gazelle, and both are quite successful mechanically, being remarkably fast runners."
...

"An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble. It can go in for elegant and fanstastic forms of support like that of the daddy-longlegs. But there is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. A man coming out of a bath carries with him a film of water about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight of water. A wet fly has to lift many times its own weight and, as everyone knows, a fly once wetted by water or any other liquid is in a very serious position indeed. An insect going for a drink is in a great danger as man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water -that is to say, gets wet - it is likely to remain so until it downs. A few insects, such as water-beetles, contrive to be unwettable; the majority keep well away from their drink by means of a long proboscis."
...

"Such are a very few of the considerations which show that for every type of animal there is an optimum size. Yet although Galileo demonstrated the contrary more than three hundred years ago, people still believe that if a flea were as large as a man it could jump a thousand feet into the air. As a matter of fact the height to which an animal can jump is more nearly independent of its size than proportional to it. A flea can jump about two feet, a man about five. To jump a given height, if we neglect the resistance of air, requires an expenditure of energy proportional to the jumper's weight. But if the jumping muscles form a constant fraction of the animal's body, the energy developed per ounce of muscle is independent of the size, provided it can be developed quickly enough in the small animal. As a matter of fact an insect's muscles, although they can contract more quickly than our own, appear to be less efficient; as otherwise a flea or grasshopper could rise six feet into the air."

Besides the beautiful prose, I like these passages because it does not succumb to the usual predictable comparisons of ability between creatures to relativise human incapability. We do, what we do. If you want to make a comparison of our abilities, pick on something our own size!

(for the full essay, "On being the right size", see http://www.physlink.com/education/essay_haldane.cfm)

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