Factor of Evolution, written in the early 1890s, is a popular example. The final chapter of the book is devoted to sociobiological explanations of human behavior, and Wilson later wrote a Pulitzer Prize winning book, On Human Nature, that addressed human behavior specifically. Edward H. Hagen writes in The Handbook of Evolutionary Psychology that sociobiology is, despite the public controversy regarding the applications to humans, "one of the scientific triumphs of the twentieth century." "Sociobiology is now part of the core research and curriculum of virtually all biology departments, and it is a foundation of the work of almost all field biologists" Sociobiological research on nonhuman organisms has increased dramatically and continuously in the world's top scientific journals such as Nature and Science. The more general term behavioral ecology is commonly substituted for the term sociobiology in order to avoid the public controversy. Theory Sociobiologists maintain that human behavior, as well as nonhuman animal behavior, can be partly explained as the outcome of natural selection. They contend that in order to fully understand behavior, it must be analyzed in terms of evolutionary considerations. Natural selection is fundamental to evolutionary theory. Variants of hereditary traits which increase an organism's ability to survive and reproduce will be more greatly represented in subsequent generations, i.e., they will be "selected for". Thus, inherited behavioral mechanisms that allowed an organism a greater chance of surviving and/or reproducing in the past are more likely to survive in present organisms. That inherited adaptive behaviors are present in nonhuman animal species has been multiply demonstrated by biologists, and it has become a foundation of evolutionary biology. However, there is continued resistance by some researchers over the application of evolutionary models to humans, particularly from within the social sciences, where culture has long been assumed to be the predominant driver of behavior. Sociobiology is based upon two fundamental premises: Certain behavioral traits are inherited, Inherited behavioral traits have been honed by natural selection. Therefore, these traits were probably "adaptive" in the environment in which the species evolved. Sociobiology uses Nikolaas Tinbergen's four categories of questions and explanations of animal behavior. Two categories are at the species level; two, at the individual level. The species-level categories (often called "ultimate explanations") are the function (i.e., adaptation) that a behavior serves and the evolutionary process (i.e., phylogeny) that resulted in this functionality. The individual-level categories (often called "proximate explanations") are the development