The Black Pines along the Main Walk were planted under the direction of John Stevens Henslow, founder of this Garden, to illustrate variation within species. Despite being the same species, the Black Pines which come from warm climates hold their branches erect, while those from cold areas have sloping branches to allow snow to slide off. This limits the load on their branches and ensures the leaves are free to photosynthesise.
This variation within species is a living illustration of Darwin’s phrase ‘survival of the fittest’, which he intended to mean ‘better suited to the local environment’ rather than in the athletic sense of the word ‘fit’. In an early natural population of trees with erect branches there would have existed some trees which by chance had slightly more sloping branches than others. These trees were more fit to survive heavy snow, and their offspring inherited the sloping branches. In the snowy areas, over millions of years, the variant with erect branches died out, and the variant with sloping branches survived.