HOW EVOLUTION SHAPES OUR LIVES

Richard E. Lenski

OUTLINE

1. Biological foundations

2. Evolution in health and disease

3. Reshaping our world

4. Evolution in the public sphere

5. Nature and nurture

Many people think of evolution as a fascinating topic, but one with little relevance to our lives in the modern world. After all, most people first encounter the idea of evolution in museums, where they see the fossilized remnants of organisms that lived long ago. Later exposure to evolution may come in courses that present the basic theory along with evidence from the tree of life and the genetic code shared by all life on earth. For those enamored of wildlife, evolution might also be discussed in programs about exotic organisms in far-away lands, often showing nature "red in tooth and claw." So it is easy to overlook the fact that evolution is important for understanding who we are, how we live, and the challenges we face.

The comic strip shown here comes from Garry Trudeau's Doonesbury series, and it reminds us that evolution is highly relevant to our lives and to society. In fact, it touches on several themes in this volume. The conversation between the doctor and patient reminds us that despite our efforts to control nature, we remain targets for organisms that have evolved, and continue to evolve, to exploit our bodies for their own propagation. At the same time, the cartoon emphasizes that humans have acquired another mode of response — the use of technology — that allows us to combat diseases far more quickly (and with less suffering) than if we had to rely on a genetically determined evolutionary response. More subtly, the technology, institutions, and language (including humor) that make human societies what they are today all reflect a process of cultural evolution that emerged from, and now often overwhelms, its natural counterpart by virtue of the speed and flexibility of cultural systems. Finally, Trudeau jabs us with the needle of the conflict between evolutionary science and religion that dominates many discussions of evolution in the public sphere, despite the overwhelming and continually growing body of evidence for evolution.

1. BIOLOGICAL FOUNDATIONS

To set the stage, we begin this volume with a question: What is evolution? From subtle shifts in the genetic makeup of a single population to the entire tree of life, evolution is the process by which life changes from one generation to the next and from one geological epoch to another. The study of evolution encompasses both the historical pattern of evolution — who gave rise to whom, and when, in the tree of life — and the ecological and genetic mechanisms that underlie the evolutionary process (see chapter 2).

When Charles Darwin published The Descent of Man in 1871, he used the comparative method to make sense of the evolution of our species. That is, he looked to the similarities and differences in the appearance and behavior of humans and our living relatives to understand how we came into being. Some Neanderthal bones had been discovered, but otherwise there was no fossil record of hominids — the taxonomic family that includes humans and the great apes — in his time. It would be several decades before much older fossils were discovered that began to fill in some of the so-called "missing links," and the insights from DNA lay more than a century ahead. Today we have a bounty of fossil hominids, and DNA from both living organisms and fossils is providing new insights into what makes us human, where we came from, and even who mated with whom (see chapter 3).

One of the important attributes of humans is that we live in social groups that require a substantial level of cooperation — in hunting game, rearing a family, and dividing the tasks of labor seen in modern societies. But cooperation is not unique to humans, or even to our close relatives (see chapter 4). Social insects, for example, exhibit remarkable cooperation and division of labor. Within ant colonies and beehives, most individuals forgo reproduction while supporting reproduction by their queen, who is usually the sister of the nonreproductive workers. In other cases, unrelated individuals cooperate, as in mutualisms involving different species, such as the fungi and algae that together make lichens. Understanding the evolutionary forces that promote these different forms of cooperation sheds light on our own behaviors as humans, as well as on some of our commonalities with other organisms whose behaviors have been shaped by these same forces.

One approach to understanding the evolution of human behavior is to ask whether our actions are, in some sense, optimal. Do humans consume food in a manner that optimizes nutritional status? Are children born at intervals that maximize reproductive success? The recognition that there might be trade-offs — for example, between the number of children and the probability they will survive to adulthood — allows the possibility, at least, of defining optimal strategies in mathematical terms (see chapter 5). However, the conditions in which our species exists have changed greatly as a result of our ancestors' migrations across the planet, as well as technological...