The Evolution of Obesity

Conclusion: Surviving the Perils of Modern Life

317 CONCLUSION Surviving the Perils of Modern Life These are very exciting times for biology; our knowledge is increasing at an exponential rate. New scientific techniques allow glimpses of the very core of life, the intricate molecular mechanisms that enable animals to function. The more we learn, the more we are amazed by the diversity, flexibility, and adaptability of life. In this book we examine a broad range of biology relevant to human obesity. Our approach is comparative and based on the foundation of evolution. We try to integrate multiple levels of analysis, from the molecular to the organismal and even to the very structure of our communities. We approach the topic from an evolutionary perspective, from a broad viewpoint, such as an examination of diverse functions of ancient information molecules, to specific features of human evolution. We examine biology that is likely common to most mammals or even most vertebrates and some biological features that appear to be unique to humans. We emphasize a systems approach because we believe it is the most productive path for understanding the biology and behavior of organisms . Molecular techniques provide amazing information, key insights into how life works. But in the end, none of the gut-brain peptides can function without a gut and a brain; indeed they are irrelevant without a liver, kidney, adipose tissue, and all the other organs, structures, and tissues that make up a whole organism. And at the end it is the organism that acts. We value molecular techniques; we use them in our research. We value in-depth investigations of organs and neural circuits. We value most of all putting these different levels together toward an understanding of wholebody physiology. Our ultimate goal is to put that understanding of human 318 THE EVOLUTION OF OBESITY whole-body physiology into a comparative and evolutionary context to understand not only how it works but also how it came into being. Information Molecules and Evolution All life has a common beginning; that is evident in the common molecular basis of life. Life requires the ability to transmit, distribute, and manage information, from outside and from inside the organism. We examine the functions of different molecules and how they regulate the physiology, metabolism, and behavior of animals. There are far more of those information molecules than we could possibly discuss in this book, with more being discovered every year. Still, there are a finite number of them, and most appear ancient, or derived from ancient molecules that were probably present in the first multicellular organisms, if not before. Evolution acts on what already exists. It does not design for the future; it is a synthesis of the past. In addition to learning about the functions of the specific molecules we discuss in this book, the reader, we hope, has integrated what we consider to be a fundamental concept regarding the approach to understanding these molecules. The evolutionary process has resulted in these molecules having diverse functions that can vary with tissue, with developmental stage, and always with the specific circumstances the organism finds itself under. Evolution has, in effect, co-opted these molecules to perform multiple functions beyond their original function, knowledge of which may be lost forever in the changes over hundreds of millions of years. And of course these molecules interact and affect each other’s functions . They need to be viewed from a regulatory perspective, as opposed to a structural perspective—a dynamic model with multiple inputs and outputs. That doesn’t mean that investigating a single aspect of a molecule’s function is not a productive means of increasing knowledge. Much of science advances in just that way: narrowing the focus and limiting the parameters to gain a clearer look at a phenomenon. However, no molecule or system exists in isolation, and a full understanding of both form and function comes from integrating the reductionist methodology into a more all-inclusive approach. CONCLUSION 319 We give many examples of this in the book; leptin is perhaps the best example relevant to the overall theme of the book. Yes, leptin functions as a satiety signal. It thus has direct relevance to the consideration of obesity. But leptin also functions as a developmental hormone and a reproductive hormone. A key function may be to link body condition to reproductive function. From an evolutionary perspective, leptin’s function may have been more to shut...