from wiki
The seeds of Capsicum plants are dispersed predominantly by birds: in birds, the TRPV1 channel does not respond to capsaicin or related chemicals (avian vs. mammalian TRPV1 show functional diversity and selective sensitivity). This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth which destroy such seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it disperse.
