Evidence for an Evolutionary Way of Life Introduction The Nature of Science Evidence of Evolution: 1. The Fossil Record 2. Biogeography 3. Comparative Anatomy 4. Comparative Embryology 5. Molecular Biology 6. Artificial Selection   Introduction Modern biologists recognize that evolution is the process that has transformed life on Earth from its early beginnings to the diversity of forms that characterizes it today. Evolution is regarded as the most pervasive concept in biology, providing deeper meaning and understanding to all aspects of the discipline. The celebrated geneticist, Theodosius Dobzhansky, vividly captured the essence of this perspective when he said "nothing in biology makes sense except in the light of evolution." Our modern understanding of the evolution of life began in 1859, with the publication of Charles Darwin's On the Origin of Species. In this book, Darwin presented a convincing case for evolution. He argued that species were not specially created in their present forms, but had evolved from ancestral species. Darwin coined the phrase "descent with modification" to encapsulate the idea that all organisms on this planet are related to one another through descent from an unknown ancestor that lived in the remote past. A critical component to Darwin's concept of evolution was his proposal of a mechanism to explain how species change through time and how they become better adapted to their local environments. Many of Darwin's predecessors suggested that life on Earth had evolved, but their theories were speculative and failed to adequately explain how the evolutionary process operates. The mechanism for evolution proposed by Darwin is called natural selection. According to Darwin's concept of natural selection, populations change over time because individuals with certain heritable traits leave more offspring than others. Interestingly, while some form of descent with modification was readily accepted by most of the scientific community, Darwin explanation for this process (natural selection) was being rejected. Some of the main objections to natural selection were: it lacked an explanatory theory of heredity; it attributed evolution to chance; and it could not explain all the patterns (e.g., gaps between forms) that were evident in the fossil record Darwin also indicated that evolution proceeded as a branching tree; new species arise from small populations that branch from a ancestral species. The budding of one or more new species from a parent species is referred to as branching evolution or cladogenesis. Although Darwin's theory of evolution by means of natural selection was a profound interpretation of the natural world, it was also a rather simple one. Thomas Huxley, who became Darwin's main public defender, is reported to have said, "How extremely stupid not to have thought of that!" The essence of Darwin's theory can be summarized as follows: There is a high degree of heritable variation in most natural populations. That is, populations exhibit a substantial amount of variation in form and function and this variation is passed on through the generations. Populations typically produce more offspring than can survive and reproduce successfully. The survival and reproductive success of individuals in a population are not equal. If some offspring have traits that give them an advantage under a particular set of conditions those organisms will be more likely to survive and pass on those traits to future generations. As the differences accumulate from generation to generation, this will lead to gradual change in the population such that populations of organisms will diverge from their ancestors, becoming reproductively isolated and eventually forming new species. Behind Darwin's rather simple explanation for evolutionary change and organismal adaptations was a substantial amount of evidence supporting his claims. In the 140 year period since the publication of On the Origin of Species, evidence in support of Darwin's theory of evolution continues to accrue. This essay is intended to present evidence for an evolutionary way of life. Before the evidence of evolution is presented, it will be useful to introduce a short discussion on science and the scientific method. There are certain criteria and avenues of inquiry that scientists must adhere to when attempting to interpret the natural world objectively. We certainly want to be sure that the evidence used to support evolution is in compliance with them. Indeed, many of the objections to modern evolutionary theory, result from misunderstandings about the nature of science and the scientific method. NEXT