Tuesday, 21 September 2010


I am a great enthusiast for houseleeks (Sempervivum species and varieties) and, in the main, my pleasure comes from marvelling at the symmetry of their leaf rosettes.

I have not really speculated on this arrangement of leaves, except to appreciate that it is a widespread phenomenon in nature and something to do with the Fibonacci sequence. However, today I came across a proper explanation in Michael Ruse's book The Evolution - Creation Struggle (Harvard University Press, 2006): "A popular example [of self-organization] is the widespread phenomenon known as phyllotaxis - the spiral patterns that one sees ordering the parts (seeds and flowers) of many plants, for instance, the head of the sunflower. One might think (Darwinians have thought) that this phenomenon is produced by natural selection, to maximize exposure to the sun while minimizing the amount of space needed to gain this benefit. In fact, one can show that such spirals have little or nothing to do with biological processes and are simply the results of the way in which seeds and other parts are produced. Seeds, such as those of the sunflower, are made in the center and then pushed outward. Simple formulas drawn from the branch of mathematics known as lattive theory show how these spiral effects are produced."

Ruse goes on to point out that much of what we see in the natural world that appears to be created or organised is, in fact, a natural outcome of chemical and physical processes.

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