Source Article: Genes Contribute to Behavior Differences Between Fierce and Friendly Rats
A Study dated 11/7/14 from the Genetics Society of America has examined the role that genetics plays in the temperament of rats. The study began nearly 40 years ago and involved two groups of wild rats. One group was selectively bred for aggressive behavior toward humans. The second group was bred for tame behavior toward humans. After 60 generations of rats, the two groups respond to humans in very different ways. The study went on to find gene variants that were responsible for the different temperaments and were able to identify "eight regions of the genome that contributed to the variation in tameness" among rats that were bred from crosses between one tame parent and one aggressive parent.
This study emphasizes the importance of selective breeding, not just for health and for physical characteristics, but for temperament as well. It is easy to think that all we have to do is proper socialization from birth and all of our rats will be sweet and loving. But genetics definitely plays a role. Having the wrong genetic makeup can make the socialization process more difficult, but the right genetics can also make socialization a simple and natural process.
This is something that rat owners familiar with halfies (rat litters born to one domesticated parent [usually female] and one wild rat [usually male]) already know. Despite intense socialization at a very young age, these rats usually remain somewhat wild-like and more difficult to handle, a clear sign of the influence the wild rat genes have on the domesticated rat gene pool, regardless of the best efforts at socialization.