Why do I spend so much time talking about plants ? Humans, birds, and insects all consumed plant nutrients. Humans have evolved over millions of years but it is only in the past 50,000 years that most of our human genome was formed. Plants and insects were here on Earth before we were. They interacted with plants.
The plants protected themselves with certain chemicals that repelled insects and small mammals such as guinea pigs and rabbits from eating them. The ancient plants were so rich in these repellent substances that we would consider them to be weeds today and totally inedible. A process of crossing plants to eliminate these bitter tastes is what was done as agriculture became more diverse starting 10,000 years ago. The almond for example is derived from an ancestor much like a peach pit but without the cyanide found in the fruit seed.
Other chemicals in the plant are beneficial to our metabolism such as caffeine in green tea. While two-thirds of all drugs are derived from plants, a diet rich in diverse plant foods can provide healthy antioxidants that distribute throughout the body (See What Color Is Your Diet? in paperback from Harper-Collins by David Heber and Susan Bowerman, 2001).
Many cultures consume edible flowers such as jasmine which also attract insects and smell wonderful in the evening. The exploration of the plant world for beneficial substances may be the pharmacy of the 21st century at least for prevention of common chronic diseases.