Most of us intuitively understand what nature means, but could you define it? Nature is everything in the universe except what humans have manufactured. It encompasses every substance, event, force, and energy —sunlight, flowers, animals, bacteria, rocks, thunder, humans, and so on. It excludes everything artificial. Researchers, clerics, farmers, astronauts, children— anyone who is of the mind to do so attempts to make sense of nature. Interpretations differ, for no one can be expert in everything learned so far or have foreknowledge of all that remains hidden. If you are reading this book, you are starting to explore how a subset of scientists, the biologists, think about things, what they found out, and what they are up to now.