All this new technology has allowed zoologists to study things previously impossible. The century began with the rediscovery of Mendelian genetics, followed by the discovery of DNA structure, the genetic code itself, instinct and animal behavior, speciation, hybrids, parthenoforms, a new previously unknown Kingdom of chemosynthetic organisms, restriction enzymes, cloning, genetic engineering, genetic control of development, and understanding of metabolic pathways. One of the strongest recurrent themes in biology this century has been to consider all sorts of phenomena within the context of natural selection. Phylogenetic systematics has revitalized many areas of biology, forcing and facilitating an evolutionary approach.
Evolution provides the conceptual backbone of zoology.
Zoologists study phenomena that range across vastly different spatial and temporal scales, from molecules to cells to organisms to populations to communities and entire ecosystems. Like other scientists, most zoologists have rushed to embrace the reductionistic approach. Too often, workers at different levels look somewhat askance at the next higher level of approach. The reason for this hesitancy to accept the next higher level may be that one must slur over interesting detail at one's own level in order to practice biology at the next level up. Each level of approach offers distinct advantages but suffers from its own problems.