Eugenics
The rediscovery of the scientific work of Gregor Mendel in 1900 led to modern genetics, and an understanding of how heredity worked. Mendel himself experimented on peas, and found that many characteristics of the pea plants, such as their colour or their height, could be turned on and off through heredity like a switch. For example, his peas could be either yellow or green, one or the other.