The author mentions that all of the following are aware of

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- It has also been noted by naturalists that a certain type of wasp always provides five – never four, never six.
- caterpillars for each of their eggs so that their young have something to eat when the eggs hatch - Research has also shown that both mice and pigeons can be taught to distinguish between odd and even numbers of food pieces
- the naturalist Gilbert White tells how he surreptitiously removed one egg a day from a plover‟s nest , and how the mother laid another egg each day to make up for the missing one