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Scientists Regrow Chicken Wing
An anonymous reader writes "Unlike salamanders and lizards, most animals have lost the ability to replace missing limbs. But a research team in San Diego has been able to regenerate a wing in a chick embryo — a species not known to be able to regrow limbs — suggesting the potential for such regeneration exists innately in all vertebrates, including humans." From the article: "Manipulating Wnt signaling in humans is, of course, not possible at this point, Belmonte says, but hopes that these findings may eventually offer insights into current research examining the ability of stem cells to build new human body tissues and parts. For example, he said Wnt signaling may push mature cells go back in time and 'dedifferentiate' into stem-like cells, in order to be able to then differentiate once more, producing all of the different tissues needed to build a limb."
Maybe the ability to have consequences for being stupid enough to get your leg taken off is a net positive for a species, though it's an obvious negative for an individual? I have no idea. That would be like a meta-evolution there, and kind of anthropomorphises the theory.
Lizards could have picked up the ability after birds and mammals split off from reptiles. IANA paleontologist, of course, so I have no idea when lizards picked up the ability.
Alternatively, it could simply not have been useful enough for the early mammals and birds. Selection pressure only applies to things that increase your ability to reproduce. (Survive to reproductive age, find a mate, and produce viable offspring.) And if, say, flight or fur proved to be more advantageous than regenerating a tail, flight and fur would win out.
Remember, evolution isn't a ladder, it's a tree. Or maybe a branching vine would be more appropriate an analogy. There's no absolute "better" or "worse" -- just better or worse for a particular ecological niche.
Ellen Heber-Katz, a professor at the Wistar Institute in Philadelphia, was working with mice that had been genetically engineered to develop lupus when she noticed that some of their ears looked weird. She had punched holes in them so she could separate her control from her treatment groups in an experiment. But the holes quickly grew shut without a trace -- not even a hint of a scar.
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The missing ear holes confused her research at the time, but the phenomenon launched a whole new career for Katz.
She and her colleagues wanted to find out if other parts of these mice, known as the MRL strain, would also regenerate. So they performed some tests: They snipped off the tip of a tail, severed a spinal cord, injured the optic nerve and damaged various internal organs.
All of the injuries healed, even the severed spinal cord. The results caused Heber-Katz to shift her research from autoimmune disease to regenerative medicine.
Now, thanks to Darpa's call for grant applications in regeneration, scientists all over the country from various disciplines are working together on the MRL mouse...
More at http://www.wired.com/news/technology/medtech/0,71
In coding, each feature has a cost associated with it. Nothing is free. A feature will result in the combination of one or more of the following: more design/coding time, higher memory use, more CPU use, a higher chance of bugs, etc.
Evolution is the same.
For some creatures, the advantages are outweighed by the disadvantages.
For other creatures, the disadvantages are outweighed by the advantages. For many creatures, perhaps regenerating the limb isn't that useful -- the biology of the animal might mean that the loss of a limb is general fatal due to blood loss or infection (assuming the animal survives the accident/attack, which may be unlikely).
In addition, just because a feature may be a net advantage for a creature doesn't mean that it will magically appear. Genetic mutation is a crapshoot. Regeneration might have been perfected after the split from the decendents of other animals. Or perhaps the common ancestor of (say) salamanders and mammals was capable of generation, but after the split happened, regeneration had too high of a cost for the line that lead to mammals, and the genetic code was lost or adapted for some feature that was more useful.
I hope that explanation helps.
The explanation that I am familiar with (and if there are any evolutionary biologists present, feel free to correct me) is that regeneration is too time consuming for a warm blooded animal.
With a reptile or amphibian, the wounded individual can afford to lose the weeks or more of downtime while their wounds or missing limbs regenerate. With a mammal or bird, the constant need for food to fuel a warm blooded metabolism wouldn't give a wounded individual time to heal in the same fashion; instead of regeneration, we scar instead. To use an technological metaphor, mammals slap a patch on the wound for faster recovery, while reptiles take the time to do a thorough repair job.
In any case, in the wild complete loss of limb would almost always be fatal for a mammal (barring infection or blood loss, you might live long enough to starve to death), so faster, incomplete healing via scarring is going to be good enough for most of the injuries we'd have a chance to recover from. We trade the ability to recover fully for the ability to recover quickly.
Today of course we no longer die as easily from our wounds, or from the inability to fend for ourselves after being crippled, so we have a vested interest in reworking this process. If we could induce regeneration in amputees for example, we could put them in a hospital for however long it takes to grow back and regain the use of their limbs - something we never could have done in our evolutionary history.
Erotic is when you use a feather. Exotic is when you use the whole chicken.
I don't remember where I read it (probably in another /. post), but the ability to regrow limbs and the ability to build scar tissue are mutually exclusive. Mammals, what with our speedy metabolism's constant need for food, generally cannot spare the time or energy that a reptile or amphibian can to regrow a missing limb or tail, and instead build scar tissue over the wound as sort of a "quick-fix". Evolutionarily speaking, the ability to heal quickly is more favorable than the ability to regrow a limb by sitting around and waiting. We simply don't have the luxury of time. Brings a whole new meaning to "scarred for life", eh?
I hope science figures this stuff out soon, I would like to get my foreskin back.
Just because we don't know what "junk DNA" is for doesn't mean it's not useful.
Researchers are starting to point this out.
A recent example: The sequencing of the DNA of the domestic chicken found a 20,000-base-pair "non-coding" (i.e., "junk") sequence that is very nearly identical with a sequence in human DNA. For such a long sequence to be preserved is highly unlikely unless it has a strong adaptive advantage. We don't have any idea what it does, but the only reasonable conclusion is that it's very important to both chickens and humans. That's the only way it could have been preserved for the roughly 180 million years since our last common ancestor.
Either that, or it's a retrovirus that infects both species and recently invaded both genomes. Possible, but a lot less likely.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.