|MadSci Network: Anatomy|
I believe you are referring to this website: http://www.sciencenet.org.uk/database/bio/animals/mammals/primates/ b01047d. html There are several levels to your question, so I will try and address them all. First of all, humans do in fact have tails early in embryonic development - Fallon & Simandl (1978) wrote an article in the American Journal of Anatomy describing how this tail, present in early developmental stages, is broken down through apoptosis, programmed cell death, 4 to 6 weeks after conception. But in anatomical terms, a tail is a very specific structure, with it's own musculature, nervous connections and connective tissues - it is not just a growth of skin around the coccyx. Therefore, making such a growth by skin extension (see below) would not give you a tail, but more of a flap of skin in the right place for a tail. Living epidermis is very malleable. You can get skin to grow into many different shapes on a living donor. This is the basis of many plastic surgical techniques, including those used in reconstruction after cancer or burns. But you are usually talking about skin measured onthe scale of centimeters or inches. So this sets up your "parachute" idea. Many animals use stretched skin to help them glide. The skin is stretched between structural "stringers" (ribs in the case of Draco volans, the malaysian flying dragon; between the toes inthe asian gliding tree frog Rhacophorus reinwardtii, between the forearms and hindlimbs in the mammalian sugar glider - Petaurus breviceps). These gliding membranes are not true wings as would be observed in birds, bats or pterosaurs, but they do tend to give the organism a reasonable glide ratio. However, the problems of the human epidermal parachutist would be numerous, and all of them are based around the central aerodynamic concepts of lift vs drag. Somehow you have to generate enough lift to give your 50-100 kg unaerodnamic human body a decent glide ratio, i.e., one that will end up with you being able to land without many weeks in traction. There is an excellent description of glide ratios here: http://www.cmnh.o rg/dinoarch/2001Jan/msg00441.html There have been some remarkable bits of engineering in terms of specialized flight gear, suits with built in "winglets" that can reduce the terminal velocity of a skydiver from 100+ mph to about 50 mph. These "birdman suits" can be seen here: http://www.human flight.com/skyflying/challenge.html However, the suit alone only slows one to a very hard, probably terminally hard, landing which will probably trash the human landing gear, especially if said landing gear happens to be your head. In order to make an epidermal "parachute" you would need other, more significant biomods, including arm extension (to increase the surface area) and some form of muscle modification - humans, unlike birds, have solid heavy bones and have relatively low strength to weight ratios. You'd probably need to have bionic modifiers to increase pectoral and arm (and possibly leg) muscle strength to keep your "flaps" extended, not to mention maneuvering them so that you don't just glide in on your belly, head, back, or other inappropriate landing devices. This would be supporting a skin membrane which would be significantly larger than the rest of your body. Using hang gliders as a good model, an 80 kg (200 lb) pilot, needs a glider with >200 sq feet lift area. Need a lot of extra skin. So short answer, it's probably not a practical way to save yourself from a building. I would recommend a fire escape. Or a hang glider.
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