A Burning Question?
First … sorry. You’ve probably already turned this paper in, because it takes me so long to get through all the questions you guys send in, but in case anyone else is writing a research paper on the "Biological Manifestations of Burns and Possibilites for Evolution of Hominid Daenarysian Flame-Resistance," here ya go:
Bodies are made of cells. Cells are made primarily of proteins, fats (called lipids), nucleic acids (like DNA) and most of all, water. Burns are really just an injury to these cells caused by exposure to high temperatures. The severity depends on how many and which kind of cell gets burned.
The burning that happens when we touch a hot iron must be differentiated from the burning that happens inside, say, a campfire. In a campfire we are witnessing combustion. This is the conversion of one type of chemical - long chains of carbons that make up wood, for instance - into simpler carbon chains, like ash. Oxygen feeds the reaction and water vapor is released. Processes like cremation burn a body this way, but it takes very high temperatures (and usually some external propellant) to recreate something like the famous self-immolation of Thich Quang Duc, or when Sarah Conner was toasted by a thermonuclear weapon.
We are all aware that the severity of burns ranks into three categories, but you might not know that the more severe burns, while most dangerous, hurt the least. Why is that? Let’s analyze what happens to your cells when you get burned.
Depending on the temperature and length of exposure, your cells will absorb a certain amount of heat. The more heat, the deeper the burn and more severe. Let’s pretend we had a thin sheet of cells on a stove and started cranking up the temperature.
First the cell membranes, made of lipids and other molecules, would start to lose their shape. Just like olive oil is liquid at room temperature and solidifies in the fridge, so do the fats in your cell membranes respond to extreme temperatures.
Next, the long, carefully wound chains of amino acids that make up your proteins would begin to unravel, just like a wrinkle relaxes when you iron a shirt. Instantly, all the machinery of your cells would be unwound and useless, never able to fold up into its active shape. If you’re keeping score, that means you have loose membranes filled with broken proteins. That cell is D-E-D dead.
If the temperature gets high enough, the water in the cells will actually boil away! Depending on how hot and long the exposure, you’re left with some region of your tissue that is effectively burnt toast. Of course, it doesn’t end there. Your body recognizes the injury and starts to release a whole mess of emergency signaling molecules around the burned tissue. One of these is called histamine, and it actually causes gaps to form between cells, allowing fluid to leak out. This is why liquid-filled blisters (that you, of course, never pop) form, and also, along with some other causes, why you get the sniffles.
Along with the tissue itself, your blood vessels can also get damaged, and unless they grow back (which they don’t always do), you could be left with a pretty bad situation. This is why we give grafts of living skin tissue, so that we can patch a dead region with something that’s still alive. Beyond that, your body’s response to severe burns can be as severe as kidney failure, shock, and loss of immune protection.
Basically, in order for humans to progress into fireproof beings, we have two choices: Evolve thermostable proteins that can withstand high temperatures (like hot springs bacteria) along with Teflon-impregnated skin, or stop being made primarily of water. Both are unlikely, although could spawn a good sci-fi story or two.