In his "Phytologia" (1800), Darwin wrote “from the sexual, or amatorial generation of plants new varieties, or improvements, are frequently obtained”. He insisted in "The Loves of the Plants" that sexual reproduction was at the heart of evolutionary change and progress, in humans as well as plants. Browne writes that the poem may be seen as "an early study in what was to be Darwin's lifelong commitment to the idea of transmutation.” Darwin illustrated not only organic change, but social and political change as well. Throughout "The Botanic Garden", Darwin endorses the ideals of the American and French revolutions and criticizes slavery. His celebration of technological progress in "The Economy of Vegetation" suggests that social and scientific progress are part of a single evolutionary process. Humanity was improving, moving towards perfection, as evidenced by abolitionism and the broadening of political rights.