Catalogue number: WP6/5/5(7)
Manuscript chart drawn by Wallace, showing variation in birds for his book on Darwinism, undated, probably 1888.
This chart, hand-drawn by Wallace, illustrates variation in the wing and tail measurements of seven species of birds. Wallace planned to use the chart in chapter three 'The Variability of Species in a State of Nature', of his book Darwinism: An Exposition of the Theory of Natural Selection with Some of its Applications.
When the book was published in 1889 only three of the examples prepared were actually used - Geothlypis trichas (common yellowthroat), Pipilo erythropthalmus (eastern towhee) and Cardinalis virginianus (American songbird), appear as figure three in chapter three.
In the accompanying text Wallace explains his diagrams: 'The first of these is intended, mainly, to show the actual amount of the variation, as it gives the true length of the wing and tail in the extreme cases among thirty specimens of each of three species. The shaded portion shows the minimum length, the unshaded portion the additional length in the maximum. The point to be specially noted here is, that in each of these common species there is about the same amount of variation, and that it is so great as to be obvious at a glance.'
Wallace was keen to make his science as accessible to as many readers as possible - his specific reason for using lots of illustrations and diagrams in his book. Wallace says in the preface to the book that 'an endeavour has been made to give such an account of the theory of Natural Selection as may enable any intelligent reader to obtain a clear conception of Darwin's work, and to understand something of the power and range of his great principle'.
Wallace was proud to be associated with Charles Darwin. He spent many years publicising natural selection as a mechanism for evolution and based his Darwinism book on the lecture notes from his tour of North America between 1886 and 1887.
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