Hand-drawn graph showing variation in the Baltimore oriole
Catalogue number: WP6/5/5(31)
Manuscript graph by Wallace, on variation in the Baltimore oriole bird for his book on Darwinism, undated, probably 1888.
This graph, hand-drawn by Wallace, illustrates variation in measurements of the bird Icterus baltimore (Baltimore oriole). Wallace used the features of 20 male birds to draw a scatter graph with dots showing variation in wing, tail, tarsus, hind toe, mid toe, bill length and bill width measurements. Their relative variation is represented as a fraction written on the right hand side.
Wallace planned to use this graph 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. The book was published in 1889, but only parts of the graph were actually used - tail, wing, tarsus, middle toe, hind toe, bill length, bill width (page 63, figure 9, 1889).
Wallace explains in the published text accompanying the graph that 'there is usually no very great accumulation of dots about the median line which shows the average dimensions, but that a considerable number are spread at varying distances on each side of it'. In other words, this shows there is a lot of variation in the measurements.
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