Looking Down the Tree: The Evolutionary Biology of Human Origins

Looking Down the Tree: The Evolutionary Biology of Human Origins

We know much about our history from bones and DNA, but these studies do not tell us about the characteristics that are not preserved in the fossil record ― the fleshy parts and behaviors. Evolutionary biologists are more interested in the processes of evolution than the patterns; what caused the changes we see in the fossil record? Looking Down the Tree applies evolutionary principles to understand the history of our species and the pressures of natural selection which led to our unique appearance and behaviors. Cruzan draws upon evidence from fossils, genomics, phylogenetics, coalescence theory, and the anatomy and physiology of our human ancestors and other animals to arrive at an understanding of the origin of human appearance and behavior. This evidence is discussed in the context of comparative biology, natural and sexual selection, evolutionary constraints, inbreeding and inclusive fitness, and genetic and cultural evolution. The story of our past that we piece together provides a novel view of how savanna habitats favored a unique set of adaptations including bipedalism and the loss of fur in our early australopithecine ancestors. Other characteristics were outcomes of increasing brain size, which led to the birth of helpless infants that required years of childcare. Cooperation was favored through inbreeding and inclusive fitness in the clans of our ancestors as they struggled to survive through extensive periods of severe drought in eastern Africa. We end this discussion with an evaluation of the increasing importance of cultural evolution, as the transmission of skills and knowledge became ever-more important for human life. Like any other species, we discover that we are the product of the environments that our ancestors experienced. "Mitch Cruzan's research is on evolutionary processes in plants, but he has studied in depth the published research on the fossil record and genetic aspects of human evolution. His clear description of how our species evolved, and how this accounts for unique human characteristics, is peerless. I found his treatment fascinating and deeply rewarding." -- Doulas Futuyma, Distinguished Professor Emeritus Department of Ecology and EvolutionStony Brook University "An entertaining and informative exploration of the evolutionary journey that led to us." -- Jonathan Losos, Professor of BiologyWashington University, St. Louis "How modern humans evolved is among the most scientifically interesting-and the most socially contentious-topics in all of science. Drawing on the full toolkit of contemporary evolutionary biology, Mitchell Cruzan's Looking Down the Tree offers a succinct, lively, and provocative account of human evolution." -- Glenn Branch, Deputy Director, National Center for Science Education "This slim volume offers a succinct and entertaining introduction to the human evolutionary story. Cruzan has successfully produced a compelling narrative that draws together many fascinating aspects of the human evolutionary story." -- Choice Mitchell B. Cruzan is Professor of Biology at Portland State University. He received his BA and MA in Biology from California State University, Fullerton, and his PhD from Stony Brook University. He is currently an associate editor for Molecular Ecology, a leading journal in the field. He has previously published an advanced textbook, Evolutionary Biology: A Plant Perspective (OUP, 2018).