I do not believe it would be possible to revive a dead body 4 years (or at anytime really) after death for several reasons. First, the type of cloning that scientists can perform is not taking adult cells and recreating those same adult cells. Cloning of an animal would mean taking the DNA from an adult cell and putting it in an egg from the same species of animal that does not have a nucleus of its own. This egg would then be put into the womb of another animal of the same species where it would develop into a fetus, just like any new animal that is going to be born. This can be done for many types of animals myfriendagain (commercial website for cloning dogs) but only while they are still alive or right after they have died. If you wait too long the DNA molecules will lose their structure and will no longer be able provide the genetic information necessary to recreate the animal. Imagine trying to read a very old book in which the ink has faded away in places, you may be able to understand bits and pieces but you won’t get the whole story. This is what happens to molecules in animals after they die, but much more quickly.

Another reason you would not be able to revive a dead body is because once something is “dead” it means that all the electrical activity in the brain has ceased and no one has been able to figure out how to restart those electrical currents. Neurons are like wires in the brain that carry electrical charges. However, these charges are in the form of ions, single atoms that have either lost or gained an electron and now have an overall positive or negative charge. Two of the main ions used by neurons are potassium (K+) and sodium (Na+). These ions are present in the brain inside and outside of neurons in unequal concentrations; there are many more Na+ ions outside of neurons and many more K+ ions inside neurons. When your neuron sends a signal, Na+ ions flow into the neuron and K+ ions flow out based on diffusion across their gradients (remember, molecules always flow from areas of high concentration to low concentration). When electrical activity in the brain stops, the concentration of ions outside and inside the cell is the same and there is no force to drive their motion inside or outside of the cell. You can think of this like a battery dying, eventually it reaches a point where its electrical charges have no force and it must be recharged. However, no one currently knows how to recharge the neurons of a dead animal, as the brain is much more complex than a simple battery, with ~85,000,000,000 neurons in the human nervous system.

So overall, there is no way to restart the electrical charges in the brain of a dead animal because we do not know how to recharge the complicated neural complex. We cannot clone an identical adult animal, and we could not clone any animal in general from DNA that has been decaying for several years. The best you could do would be to have fresh DNA from a living (or very recently deceased) animal, put it in an egg, and grow a whole new animal. This animal would have all the same genes as the parent the DNA came from, but may not look or act exactly the same because of the different environment it developed in.

Besides cloning, we have developed technology using things called “stem cells”. You may have heard that this year’s Nobel Prize in medicine went to two scientists who discovered stem cells (http://www.nobelprize.org/nobel_prizes/medicine/ laureates/2012/). These are adult cells that have been treated so that they can become any cell type in the body. If you look at your body, you will notice there are many different types of cells (hair, skin, nails, to name a few) but they all have the exact same DNA. The only difference between these cells is that certain genes are being expressed and others are not, depending on what type of cell it is. Adult generated stem cells are cells that have already become a specific tissue (skin for example), but have been reset, so now they can turn into any cell type (blood cells for example). However, these cells need cues from their surroundings to figure out what to become. Therefore, if you only have a decaying skeleton, there will be no other surrounding cells to tell stem cells what types of tissues they should form. This means you could not form an entire new body off of a skeleton using stem cells. Hope that helped you!

Cloning has been only partially successful - the methods of cloning known have problems (cloned individuals age at an accelerated rate).

There are chemicals that are more effective at preserving a dead body. These chemicals are extremely toxic - the reason why they are so good at preserving the body is because they kill any bacteria or other organisms that are trying to decompose it. So while the body might remain in the same apparent state as when the animal died, the preservation pretty much guarantees that it stays dead.