Alkaloids

Alkaloids are bitter-tasting toxins that appeared in plants about the time that mammals evolved, and seem especially effective at deterring our branch of the animal family by both taste and aftereffects. Almost all known alkaloids are poisonous at high doses, and most alter animal metabolism at lower doses: hence the attractions of caffeine and nicotine. Among familiar foods, only the potato accumulates potentially troublesome alkaloid levels, which make greened potatoes and potato sprouts bitter and toxic.