The military is investing heavily in labs which are studying genes related to regeneration—specifically, the ability to regenerate limbs and organs. The motivation behind this is clear. As soldiers in Iraq and beyond are surviving wounds that previously would have been fatal, often their injuries include amputations which prevent them from returning to duty. The ability to replace lost limbs would be an awesome advancement in military medicine, and medicine in general. But is it really possible?
Other animals, such as salamanders, are able to spontaneously regenerate lost limbs and heal scars perfectly throughout their life. Several research teams in the US believe that humans may also be able to one day regenerate tissues through the help of the genes Tbx5 (arms) and Tbx4 (legs). In humans, these genes are inactivated before birth to prevent duplicate legs and arms, however several projects to try to “re-activate” these genes in mice are now underway.
They already know that when the Tbx genes are inactivated in mice during fetal development, they don’t develop forelimbs or hind limbs, and humans born with partially defective Tbx5 genes will have severely stunted arms.
A newt takes six to eight weeks to regenerate a functional limb and a few weeks more to complete a perfect replacement. If humans had the same regenerative capacity, it would probably take a year or more to grow a new arm or leg. It’s this long regeneration time that scientists believe led evolution to favor rapid scar formation in humans and other mammals as a better route to survival in hostile environments.
(Hat tip Bob Abu.)