Warrior plants and butterflies
There were bows and arrows earlier; then came the guns, bombs, fighter planes and so on. Humans have been inventing new weapons to overpower their competition since long time. Butterflies, cute little flying insects and the plants on which they feed too have to play an arms race with each other.
A story about how the battle is played between a family of plants (which mustard and cabbage is a member) and a family of butterflies was published recently (Edger et al., 2015). Larvae of the ancestors of this butterfly family fed themselves on the ancestors of cabbage family since time unknown. About 90 million years ago some genetic changes in the plant family allowed it to make one type of chemical called glucosinolate. This was toxic to the larvae. A lot of them must have died after eating such plants that were able to produce this chemical. Within 10 million years, the changes in butterfly genome enabled it to produce one protein (nitrile-specifier protein) which was able to neutralize the toxic chemical. The butterflies that produced the protein survived. In turn the plant too diversified its chemical to evade the detoxifying effects of the butterfly protein. Those that modified their chemical had more chance to avoid themselves being eaten and thus multiply. With time, both, the butteflies and the plant diversified. They are still fighting out there and always would.
Edger, P.P., Heidel-Fischer, H.M., Bekaert, M., Rota, J., Glockner, G., Platts, A.E., Heckel, D.G., Der, J.P., Wafula, E.K., Tang, M., et al. (2015). The butterfly plant arms-race escalated by gene and genome duplications. Proceedings of the National Academy of Sciences of the United States of America 112, 8362-8366.