Placing the frog on the spine refers to the previous two book covers; where the frog became the icon of the series. This, with the use of the original 1979 typography, makes reference to the first publication.
The gold lines in the background refer to Charles Darwin’s first sketches on the theory of evolution: visually linking everything together. This element of the design provided a challenge for printing, but I was determined to keep the gold foiling as it was integral to my design.