Fruit Flies, Spiders and Genetic Iron-Knee Scientists searching for an explanation for why some spiders have longer legs than others have stumbled upon a gene they believe explains how knees developed in Earth's earliest creatures. Even more interesting is the fact that the knee gene, comically labeled the dachshund gene, did not produce knees in the ancient fruit flies in which it first appeared but mutated in spiders to produce the leg joints that give them their incredible mobility. The research was conducted by scientists with the G�ttingen Center for Molecular Biosciences in Germany, who published their findings in the journal Molecular Biology and Evolution on Oct. 6 http://mbe.oxfordjournals.org/ . Knee joints are significantly different from the ball and socket joint (hip and shoulder) and the pivot joint (elbow). Knees are condylar joints which allow for a simultaneous range of motion, rotation and weight bearing far greater than either ball and socket or pivot joints. The researchers observed that spiders without knee joints were far less mobile and did not survive as long as spider with knees, suggesting that the development of knees was a critical part of the increased mobility that allowed creatures to move faster, as well as acquire food and keep from becoming it. Scientists studying the dachshund gene as part of the leg length study noticed a second dac gene, dac2, present in spiders. When the gene was deactivated, using a process known as RNA interference, the knee joints disappeared. In their report, researchers theorize that spiders likely experienced gene duplication of the original fruit fly gene, which eventually led to the development of knees and the ability to do things like, well, catch fruit flies. Oh, the iron-knee!