[nightshade]

There is a thread on the site about this interesting subject the main concensus is that seeds and the fruit surrounding them work to ensure as far as possible the seed in not wasted in feeding an animal but ejected asap to promote the species.
In many cases seed and animals have evolved together,wheras we are comparatively recent,birds for instance have a short quick digestive system ours is long so poisons have more time to actwhile they only cause the seed to be ejected from the bird
Diffrent seeds have different stratageys for survival some are poisonous to everything!