These thread all seem to merge together eventually but I think this information applies to this topic. I found a great article that applies to this topic. Here is some of the information and the link, since no one has posted on this thread in a while hope you don't mind the long citations if so feel free to clean up or let me know and I will do it myself. [blockquote]A basic principle to remember is that animals with large, complex brains are less governed by innate behavior patterns. For example, bird behavior is governed more by instinct than that of a dog, whereas an insect would have more hard-wired behavior patterns than that of a bird. This principle was clear to Yerkes (1905) who wrote: Certain animals are markedly plastic or voluntary in their behavior, others are as markedly fixed or instinctive. In the primates plasticity has reached its highest known stage of development; in the insects fixity has triumphed, instinctive action is predominant. The ant has apparently sacrificed adapt-ability to the development of ability to react quickly, accurately and uniformly in a certain way Roughly, animals might he separated into two classes: those which are in high degree capable of immediate adaptation to their conditions, and those that are apparently automatic since they depend upon instinct tendencies to action instead of upon rapid adaptation. When dogs are raised in barren and nonstimulating environments they are also more excitable (Walsh and Cummins, 1975; Melzak and Burns, 1965). Schultz (1965) stated, "when stimulus variation is restricted central regulation of threshold sensitivities will function to lower sensory thresholds." Krushinski (1960) studied the influence of isolated conditions of rearing on the development of passive defense reactions (fearful aggression) in dogs and found that the expression of a well-marked fear reaction depends on the genotype of the animal. Airedales and German shepherds were reared under conditions of freedom (in homes) and in isolation (in kennels). Krushinski (1960) found that the passive defense reaction developed more acutely and reached a greater degree in the German shepherds kept in isolation compared to the Airedales. In general, animals reared in isolation become more sensitive to sensory stimulation because the nervous system attempts to readjust for the previous lack of stimulation. Countless examples of serious problems caused by continuous selection for a single trait can be found in the medical literature (Steinberg et al., 1994; Dykman et al., 1969). People with experience in animal husbandry know that overselection for single traits can ruin animals. Good dog breeders know this. Sometimes traits that appear to be unrelated are in fact linked. Wright (1922, 1978) demonstrated this clearly by continuous selection for hair color and hair patterns in inbred strains of guinea pigs. Depressed reproduction resulted in all the strains. Furthermore, differences in temperament, body conformation, and the size and shape of internal organs were found. Belyaev (1979) further showed that continuous selection for a calm temperament in foxes resulted in negative effects on maternal behavior and neurological problems. The fox experiments also found graded changes in many traits over several years of continuous selection for tame behavior. Physiological and behavioral problems increased with each successive generation. In fact, some of the tamest foxes developed abnormal maternal behavior and cannibalized their pups. Belyaev et al. (1981) called this "destabilizing selection," in contrast to "stabilizing selection" found in nature (Dobzhansky 1970; Gould, 1977). http://www.grandin.com/references/genetics.html[/blockquote]