century, the application of these techniques in zoology has increased the understanding of animal populations. In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy. Ethology Ethology is the scientific and objective study of animal behavior under natural conditions, as opposed to behaviorism, which focuses on behavioral response studies in a laboratory setting. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many future ethologists. A subfield of ethology is behavioral ecology which attempts to answer Nikolaas Tinbergen's four questions with regard to animal behavior: what are the proximate causes of the behavior, the developmental history of the organism, the survival value and phylogeny of the behavior? Another area of study is animal cognition, which uses laboratory experiments and carefully controlled field studies to investigate an animal's intelligence and learning. Biogeography Biogeography studies the spatial distribution of organisms on the Earth, focusing on topics like dispersal and migration, plate tectonics, climate change, and cladistics. It is an integrative field of study, uniting concepts and information from evolutionary biology, taxonomy, ecology, physical geography, geology, paleontology and climatology. The origin of this field of study is widely accredited to Alfred Russel Wallace, a British biologist who had some of his work jointly published with Charles Darwin. Molecular biology Molecular biology studies the common genetic and developmental mechanisms of animals and plants, attempting to answer the questions regarding the mechanisms of genetic inheritance and the structure of the gene. In 1953, James Watson and Francis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject. While researchers practice techniques specific to molecular biology, it is common to combine these with methods from genetics and biochemistry. Much of molecular biology is quantitative, and recently a significant amount of work has been done using computer science techniques such as bioinformatics and computational biology. Molecular genetics, the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other