In “Subspeciation in the Meadow Mouse, Microtus pennsylvanicus, in Wyoming, Colorado, and Adjacent Areas,” Sydney Anderson meticulously examines the ecological and genetic variances within populations of the meadow mouse across diverse geographical locales. Utilizing a combination of field studies and genetic analysis, Anderson presents a compelling exploration of subspeciation processes, effectively intertwining empirical data with a comprehensive review of existing literature on rodent ecology. The work is notable for its clarity and precision, marking a significant contribution to mammalogy and emphasizing ecological adaptability in response to environmental pressures. Sydney Anderson, a prominent figure in wildlife biology and ecology, draws upon extensive fieldwork and academic training in evolutionary biology. His passion for pequenos mammal populations and their habitats is evident throughout the text. Through years of research in the Rocky Mountain region, Anderson has developed a nuanced understanding of how minor ecological shifts can lead to substantial evolutionary changes, motivating his deep-dive analysis of Microtus pennsylvanicus. This book is essential for ecologists, biologists, and conservationists interested in subspeciation dynamics and the ecological significance of habitat variability. Anderson's rigorous approach presents not only new insights into meadow mouse populations but also broader implications for understanding biodiversity and conservation strategies in changing environments.