What is adaptation by natural selection? Perspectives of an experimental microbiologist

Ever since Darwin, the role of natural selection in shaping the morphological, physiological, and behavioral adaptations of animals and plants across generations has been central to understanding life and its diversity.New discoveries have shown with increasing precision how genetic, molecular, and biochemical processes produce and express those organismal features during an individual's lifetime.When it comes to microorganisms, however, understanding the role of natural selection in producing adaptive solutions has historically been, and sometimes continues to be, contentious.This tension is curious because microbes enable one to observe the power of adaptation by natural selection with exceptional rigor and clarity, as exemplified by the burgeoning field of experimental microbial evolution.I trace the development of this field, describe an experiment with Escherichia coli that has been running for almost 30 years, and highlight other experiments in which natural selection has led to interesting dynamics and adaptive changes in microbial populations. Evolution, natural selection, and geneticsThe fields of biology and evolution have come a long way since Charles Darwin published The Origin of Species in 1859.Nonetheless, Darwin is celebrated for the big ideas that he got right, including descent with modification and adaptation by natural selection.The former refers broadly to the fact that evolution has occurred such that organisms living today are different from their ancestors.Natural selection is the evolutionary process that explains the match, or fit, between features of organisms and the environments where they live.Jean-Baptiste Lamarck and other natural philosophers had previously put forward the idea of evolution in the general sense of descent with modification.And Alfred Russel Wallace, a younger contemporary of Darwin, independently came up with the concept of adaptation by natural selection.Neither space nor expertise allows me to do justice to the history of these ideas, except to note that Darwin is better known today than Wallace because Darwin brought to bear an extraordinary range of relevant evidence and insights that have, by and large, stood the test of time.When Darwin was rushed at the age of 50 to publish The Origin by virtue of Wallace's discoveries, he produced a 502-page volume rich with insights and details that he