Humanity’s ability to exploit almost every corner of this earth was partly predicated on his ability to consume vastly different types of plant and animal life. But moving into a new environment and trying new foods posed a danger that the new food might contain potent toxins. Luckily, our liver and kidneys evolved to handle most brushes with novel-but-slightly-poisonous plant matter – at least to keep us alive anyway if the stomach didn’t regurgitate it first. Our keen senses of smell and taste also helped us sort out the good from the bad. The reason we have a sweet tooth today (dammit) is probably an evolved response to an almost universal truth in the plant world that just about anything that tastes sweet is safe to eat.
Today you can avoid exposure to chemical toxins in your food (pesticides, herbicides, chemicals, etc) and on your skin. But also try to avoid the hidden poisons in foods like sugars, grains, processed foods, trans and hydrogenated fats, and mercury in certain fish.