Darwin’s dark matter: utter extinction

Figures & data

Figure 1. The diagram Charles Darwin drew in 1837 in his Notebook B. Darwin marked the living species with a short T-junction. The unmarked ends of other lines represent extinct species. In 1859 Darwin would call such species, which had left no descendants, ‘utterly extinct’. The three species marked A form a distinct genus. Six intermediate species, which would have linked them to C, are extinct.

Figure 2. Page 36 of Darwin’s Notebook B, CUL-DAR121. Reproduced by kind permission of the Syndics of Cambridge University Library. Beneath the diagram we can read ‘Thus between A and B immense gap of relation, C & B. The finest gradation, B & D rather greater distinction Thus genera would be formed. Bearing relation’.

Figure 3. The fold-out diagram in Charles Darwin’s 1859 Origin of Species. Besides picturing the multiplication of species, this illustrates the idea he called the Principle of Divergence. The chance of a form persisting is greater the more it differs from its relatives. Out of the original genus consisting of eleven species, A through L, only F survives the passage of time intact. A and I are extinct, but they have left descendants; the other eight species are utterly extinct.