I have a friend who will not buy avocados on principle. "Fifty percent of the weight is the seed," he explains. He loves purchasing apples, grapes and bananas, but avocados and mangos are out. Peaches and dates are borderline -- he'll buy them on occasion, with deep misgivings.

My friend has a point - the whole fruit business is a scam. Trees need to procreate; that's why they grow seeds. But trees are not very mobile, leaving them with the problem of how to get their seeds planted a reasonable distance away (if both you and your offspring are immobile, you can't throw them out of the house at age 35). One way would be to tap a passing bird, animal or human on the shoulder and say: "Excuse me, sir, can you please take these seeds and drop them off some distance away, preferably some place with good soil, sunshine and an abundant water supply?" But most passersby would probably mumble something about a doctor's appointment and slink away. So the tree packages its seeds in colorful, tasty and nutritional pulp, and markets it as "fruit".

What is the single most important factor that differentiates Homo sapiens, human beings, from animals?

My sixth grade biology teacher began one morning lesson with that question. An argument erupted in the classroom. Communication? Higher order reasoning? An awareness of right and wrong? We were tossing around ideas and spewing sixth grade philosophy. Like a good scientist, my biology teacher challenged all of our ideas. Animals have sophisticated reasoning skills. The US Navy studied the communication of dolphins and discovered that they effectively notify other dolphins of imminent danger with a whistle from across the ocean. Primates may have even demonstrated an awareness of right and wrong. Our teacher had stumped us. Finally, she came to the climax of our lesson that day. Humans are animals, and there are no basic differences between us and them. Our naive sensibilities were shattered.