Animal Model Genetic Organisms Roundworm (Caenorhabditis elegans): This millimeter- long worm allowed scientists to test the concepts of gene therapy, to develop methods for sequencing large amounts ofDNA,and provided information about the biology of human diseases such as Alzheimer's disease and cancer. Research on this worm has also enabled scientists to develop effective control measures for plant and animal parasitic roundworms. Fruit fly (Drosophila melanogaster): Studies in this organism allowed scientists to determine that genes reside on chromosomes, and gave insight into the nature of mutations. Studies of the development of complex structures such as the eye continue to provide insight into some of the ways cell specialization is regulated and directed by DNA. Zebra fish (Danio rerio): The zebra fish, with its transparent embryos, provides an excellent system in which to study the genes that regulate vertebrate development. Additionally, zebra fish have been used in studies investigating bioaccumulation of organic compounds in the environment. Common mouse (Mus musculus): Mice are useful for genetic study because of the availability of hundreds of single gene mutations. Studies in mice demonstrated that Gregor Mendel's laws of inheritance were as applicable to mammals as to plants. Transgenic genetic analysis of mice has allowed the creation of mouse strains that mimic human genetic diseases.
Animals Who Might Think In addition to this tendency to attribute states of mind to animals that are found in humans, there were a number of cases of labeling trained behavior in animals as signs of reasoning skills. One of the most famous examples was the case of the horse, Clever Hans, in the early 1900's. Wilhelm von Osten owned a horse that demonstrated extensive arithmetic skills. When von Osten presented a written arithmetic problem to Hans, the horse would tap out the answer with his forefoot. Clever Hans also appeared adept at telling time, and answered questions about sociopolitical events by nodding or shaking his head yes or no. The horse's abilities suggested to many individuals the similarity between animal and human minds. Eventually, the Prussian Academy of Sciences discovered that Hans was not answering the questions by means of any reasoning skills, but was an astute observer of the behavior of his owner and those around him. When questions were posed to Hans, cues were provided unconsciously to the horse about the correct answer. Since horses have evolved to ascertain subtle visual cues from others in their herd, Hans was able to form a number of cued associations which led to a reward. The owner of Clever Hans was not attempting to perpetrate fraud. He believed in the possibility that a horse could have reasoning ability, but von Osten was not sophisticated in how he tested for the skills. The inadvertent cueing of an animal to respond in a certain fashion is one of the major confounding factors found in the investigation of animal intelligence. The case of Clever Hans illustrates two other problems that confound reports concerning the level of intelligence in animals. First is the problem of anthropomorphism. People develop an emotional bond with animals and interpret behavior in order to enhance the closeness they feel to them. The second problem concerns the methods used to measure intelligence. The classic case of Kohler's chimpanzees illustrates this problem. In the early part of the twentieth century, Wolfgang Kohler assessed the reasoning ability of chimpanzees to obtain food outside of an enclosure. After a rake was left in the enclosure, food was placed out of reach of the caged chimpanzees. The chimpanzees were able to use the rake to bring food to the cage. K?hler concluded that the animals had insight into the nature of the problem and used reasoning to achieve a solution. A further study, requiring the fitting together of two sticks in order to reach the food, also supported K?hler's conclusions. However, later experimentation has revealed that chimpanzees without a history of playing with sticks could not solve the problem. Apparently, in order to solve the problem, the chimpanzees needed an extensive history of playing with sticks, which enabled them to learn how sticks could be used at a later time. In solving the problem, they were using an instinctual tendency to play with sticks and scraping them over the ground.
