The Rise of Eukaryotic Organisms Eukaryotic organisms appeared during the Proterozoic era. The eukaryotic cell probably evolved from prokaryotic ancestors some time before about 1.4 billion years ago. The oldest convincing fossils of eukaryotic cells are generally considered to be those from the 1.3 billion-year-old Beck Spring dolomite of California. Eukaryotic fossil cells have also been found in chert from the approximately 850 million-year-old Bitter Springs formation of Australia. The earliest eukaryotes were animal-like protozoans. This evolution occurred when photosynthetic prokaryotic cyanobacteria were ingested by protozoans and then developed a symbiotic (mutually beneficial) relationship with them. The evolution of the plantlike eukaryotes probably occurred by at least 1.4 billion years ago. (This date has been suggested because primitive multicellular algae fossils are present in rocks 1.3 billion years old.) The eukaryotic cell was a prerequisite for the development of multicellular organisms. The plantlike eukaryotes are considered to be ancestral to the multicellular algae and higher plants. The protozoans are considered to be the ancestors of the metazoans (animals). The first multicellular organisms may have been algae. Fossils that appear to be primitive multicellular algae are known from the 1.3 billion-year-old sedimentary rocks of the Belt supergroup of Montana, and the 800 million- to 900 million-year-old Little Dal group of northwestern Canada. Multicellular algae can be found living today in both freshwater and marine environments. Fossil fungi first appear in the fossil record in the 790 million- to 1,370 million-year-old Bitter Springs formation cherts of Australia. The fossil record of fungi is poor and not well known.
Instincts and Genes Instincts are a part of all living organisms, and observable instinctive responses are only a small part of an intricate pattern. The genetic makeup of an organism dictates specific unlearned patterns of responses and variations that, in turn, determine a favorable selection of individuals within a species. Clearly, instincts in sexual selection, reproduction, food gathering, and other basic needs are critical for the survival of members of a species. In higher animals, instinctive activities are often overshadowed (and sometimes disguised) by learned patterns of responses. For example, in dogs, the pulling back of facial muscles and the showing of teeth is a response to fear and attack. In humans, laughter is a similar response to surprise, embarrassment, and uneasiness. Because of social adaptation, however, laughter takes on additional behavioral conventions. Until the early part of the twentieth century, instincts were thought to be learned responses to specific situations. Consequently, if aggression were learned, then it could be modified, changed, and unlearned. With the establishment of a genetic and biochemical foundation for instincts, research in stereotyped behavior has become part of a heated debate. In 1975, Edward O. Wilson published Sociobiology: The New Synthesis. This highly technical work found a surprisingly large audience; in it, Wilson attempted to place all social behavior on a biological basis. Although the work emphasized animal behavior, Wilson implied that all human history was also part of evolutionary biology and that his work would synthesize all the social sciences with biology. Since instincts such as aggression, selection of sexual partners, and care of the young play a prominent part in cultural activities, Wilson seems to suggest that in the future, the study of society will be grounded in neurobiology and sociobiology.
