HISTORY OF BIOLOGYThehistory of biologytraces the study of theliving worldfromancienttomoderntimes. Although the concept ofbiologyas a single coherent field arose in the 19th century, the biological sciences emerged fromtraditions of medicineandnatural historyreaching back toayurveda,ancient Egyptian medicineand the works ofAristotleandGalenin the ancientGreco-Roman world. This ancient work was further developed in the Middle Ages byMuslim physiciansand scholars such asAvicenna. During the EuropeanRenaissanceand early modern period, biological thought was revolutionized in Europe by a renewed interest inempiricismand the discovery of many novel organisms. Prominent in this movement wereVesaliusandHarvey, who used experimentation and careful observation in physiology, and naturalists such asLinnaeusandBuffonwho began toclassify the diversity of lifeand thefossil record, as well as the development and behavior of organisms.Microscopyrevealed the previously unknown world of microorganisms, laying the groundwork forcell theory. The growing importance ofnatural theology, partly a response to the rise ofmechanical philosophy, encouraged the growth of natural history (although it entrenched theargument from design).Over the 18th and 19th centuries, biological sciences such asbotanyandzoologybecame increasingly professionalscientific disciplines.Lavoisierand other physical scientists began to connect the animate and inanimate worlds through physics and chemistry. Explorer-naturalists such asAlexander von Humboldtinvestigated the interaction between organisms and their environment, and the ways this relationship depends on geographylaying the foundations forbiogeography,ecologyandethology. Naturalists began to rejectessentialismand consider the importance ofextinctionand themutability of species.Cell theoryprovided a new perspective on the fundamental basis of life. These developments, as well as the results fromembryologyandpaleontology, were synthesized inCharles Darwin's theory ofevolutionbynatural selection. The end of the 19th century saw the fall ofspontaneous generationand the rise of thegerm theory of disease, though the mechanism ofinheritanceremained a mystery.In the early 20th century, the rediscovery ofMendel'swork led to the rapid development ofgeneticsbyThomas Hunt Morganand his students, and by the 1930s the combination ofpopulation geneticsand natural selection in the "neo-Darwinian synthesis". New disciplines developed rapidly, especially afterWatsonandCrickproposed the structure ofDNA. Following the establishment of theCentral Dogmaand the cracking of thegenetic code, biology was largely split betweenorganismal biologythe fields that deal with whole organisms and groups of organismsand the fields related tocellularandmolecular biology. By the late 20th century, new fields likegenomicsandproteomicswere reversing this trend, with organismal biologists using molecular techniques, and molecular and cell biologists investigating the interplay between genes and the environment, as well as the genetics of natural populations of organisms.