Symmetry: A Very Short Introduction (Very Short Introductions) by Stewart Ian

Author:Stewart, Ian [Stewart, Ian]
Language: eng
Format: mobi, epub
Publisher: Oxford University Press, USA
Published: 2013-05-29T16:00:00+00:00

Chapter 6

Nature’s patterns

Symmetries are widespread in the natural world, and they have a strong appeal to our innate sense of pattern. Figure 37 shows three instances in biology. On the left is a butterfly, Morpho didius. There are over eighty species in the genus Morpho, and they mainly inhabit South and Central America. In the middle is the eleven-armed sea star Coscinasterias calamaria found in the seas around southern Australia and New Zealand. It can be up to 30 cm (one foot) across. On the right is a Nautilus shell, shown in cross section. The nautilus is a cephalopod, and today six distinct species exist.

The butterfly has bilateral symmetry: it looks (almost) the same if it is reflected left/right about its central axis, as if in a mirror. Bilateral symmetry D1 is widespread in the animal kingdom. Humans are an example: a person viewed in a mirror looks just like a person. In fine detail, humans are not perfectly symmetric—the face often looks subtly different when reflected; see Figure 38. For a start, Mirror-Lincoln parts his hair on the other side. Internally, there are other asymmetries in the human body: the heart is usually on the left, the intestines wind asymmetrically, and so on.

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