Dear Reader,

How many days do you wake up to breaking news about a scary-sounding virus, or a potential cause of cancer, or newly identified genes that make you better at math? In a world of fast progress and easy access to information, it can be difficult to know how much confidence we should have about such reports.

My mission is to help you become more aware of the beauty and the utility of biology, and to help you evaluate the sometimes conflicting messages about science topics and science-related issues. If you could learn anything from reading this book, I hope it would be this: Biology is about you, and it touches your life every day in dozens of ways. It’s creative. And it’s fun.

There are two versions of this third edition of What Is Life? A Guide to Biology. One of them, What Is Life? A Guide to Biology with Physiology, includes all sixteen chapters of the other version, with an additional ten chapters on plant and animal physiology. It’s not always possible to include these additional chapters in a one-term course, but they provide a rich introduction to the importance of biology, with particular significance for human health.

In these pages, you’ll find an overview of the key themes in biology as well as detailed information and stories about meaningful topics. I hope you will find answers to questions you’re curious about, and will be spurred to ask many more. You’ll also find many Red Q questions, such as:

• Do megadoses of vitamin C reduce cancer risk?
• An onion has five times as much DNA as a human. Why doesn’t that make onions more complex than humans?
• Why doesn’t natural selection lead to the production of perfect organisms?
• Why are big, fierce animal species so rare in the world?

The Red Qs point toward passages that help uncover the answers. Often, the answer may not be apparent—but look again and think some more. Sometimes you know more than you realize. And sometimes it’s possible to transfer the things you learn in one context to another, helping you to recognize new connections. Understanding and developing these abilities will help you tackle novel problems, serving you well long after you may have forgotten this or that specific fact.

At the heart of scientific thinking is a determination to ask and answer questions about the world. This process of inquiry is carried out in diverse and creative ways. Within each chapter of What Is Life? you’ll find a section called This Is How We Do It. In these sections we explore the diverse ways that scientists approach problems, and how they go about finding answers. Example topics include Why do we yawn? and Does sunscreen use reduce skin cancer risk?

At the end of each chapter, you’ll find a section called StreetBIO: Knowledge You Can Use. These sections unpack some questions and issues that are particularly practical, such as How clean is that food you just dropped?

There’s much more to biology than just words. Flip through What Is Life? and look at the photographs. Images can do much more than simply illustrate ideas; they can inspire and provide an alternative hook for remembering and understanding concepts. They can also challenge you to see ideas in new ways. I have hand-picked every photo, with a goal of provoking and engaging, while helping you make connections between complex ideas.

You’ll also notice brief quotes from a variety of literary sources. There is a rich tradition of scientific imagery, references, and metaphors throughout literature. It is my hope that you will recognize that as your scientific literacy increases, your experience and appreciation of literature also will be richer.

In a world of information overload, it is more important than ever to learn how to distill ideas, examples, and implications, forming hierarchies of importance. I don’t want you to lose sight of the big picture. In organizing each chapter, I have broken down the topics into discrete, manageable sections. And at the end of each, I provide a Take-Home Message that concisely and precisely highlights and reinforces the section’s most important ideas.

Also included in the book are four-page illustrated summaries of each chapter, integrated with multiple-choice and short-answer questions. This Review & Rehearse (R&R) “mash-up” of content and quizzing reflects important insights from educational research: integrating testing to hone your retrieval abilities, while reviewing the concepts themselves, enhances your learning—taking it beyond the simple recognition that comes from just revisiting the material.

The multiple-choice questions are just a tiny sampling of the thousands of questions available to you in the online adaptive quizzing system PrepU, and each is marked with a difficulty thermometer, which reflects the difficulty of the questions based on more than 30 million responses from students nationwide.

Increasingly, the information you consume includes graphs. It’s essential to understand how to read and interpret such figures. To help you, I’ve included an exercise within each chapter called Graphic Content. This critical thinking challenge will help you become adept at reading and analyzing visual displays of information, while identifying subtle assumptions, biases, and even manipulations.

This is just a sample of some of the features in What Is Life? I hope that you find this book stimulates new ways of thinking about and understanding the world.

P.S. About the cover: I want to convey that biology isn’t something that exists far away, separate from our personal lives. Rather, it intersects with our lives and is a central part of our world.