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The methods described in pages are a theoretical discussion ONLY. Methods are discussed in only the broadest terms and I hold no qualifications in the fields discussed.
Because a method is listed here does not indicate that I approve or recommend it. In some cases, I definitely don't!

Horses and humans are both mammalian creatures and have a lot in common, biologically speaking. Skeleton, musculature, and environmental tolerances are all very similar, as they are for all mammals. Where we really vary, and what gives rise to our physical differences, is our DNA. The vast majority of tf stories rely on some technique that changes the subject's DNA from human to equine. Is this possible? What, when it really comes down to it, is this mysterious agent?

DNA, as you probably know, stands for DeoxyriboNucleic Acid. It's a long chain molecule which uses a code of proteins to store information about a life-form's traits - that is the myriad items of data that define a creature's physical shape and physiognomy. Think of it as a blueprint for a life-form. In form it is depicted as looking like a twisted ladder: two long helical strands connected by numerous rungs. In actuality it tends to be all twisted up into an incomprehensible knot. The rungs, which are composed of groups of units called nucleotides, contain the coded information that makes genes - the instructions sets that prompt cells to behave in certain ways, by producing substances called proteins. Proteins control everything within a cell, such as how it interacts with its neighbours to perform specific tasks: bone cells are not the same as blood cells or "soft tissue" cells, for example. Proteins can prompt a cell to replicate itself, or to pass messages to its neighbours, or to contract/expand, etcetera.

The "code" within a strand of DNA is not "Read Only": it can be changed. Rearranging, adding, or removing the nucleotide rungs changes the codes. This is how mutations occur. Exposure to radiation damages DNA for example. Viruses operate by splicing their own DNA into the hosts to force a cell to make more copies of the virus. It is entirely possible to replace a cell's DNA with completely different DNA. Before you get too carried away, however, merely injecting a cell with foreign DNA is not going to turn you into a horse.

Genetic Engineering has been around for a while now. Behind all the scare-mongering about not eating GM crops, do you actually know what a genetically modified crop is? In one instance, a segment of DNA from an arctic fish that produces a biological antifreeze can be added to a plant to make it more cold resistant. There are other examples, but the plant still looks like a plant. It doesn't start growing gills and scales.

Another famed example are the pigs whose bodies contain genetically human cells - the idea is to create transplant donors. Scientists call such creatures chimeras after the mythical creature who was part lion, part goat, and part serpent. But the pigs don't turn into humans, despite being one of our closest genetic relatives (there's something kind of appropriate about that, don't you think?).

What's going on then? Why doesn't changing DNA change the body's physical shape?

Well, most of the cells in your body are programmed, from your DNA, to perform a specific function, to reproduce themselves, and to die - in the case of skin cells, their death is actually required before their role is finished! The vast majority of cells are basically happy in their assigned role, happy with their location, and disinclined to move. If the cell's DNA were somehow replaced with equine DNA (which is possible) then the cell would simply begin to produce different proteins. It's function might change. It is very likely to alert the body's immune system and be destroyed. It is unlikely to perform the function it previously did. In short, you probably wouldn't survive very long.

An analogy would be to think of DNA as a computer program containing instructions (genes) for a specific life form. If you take the software from a pocket calculator and bung it into, say, a microwave oven, the code will live in the microwave's memory perfectly well, but you won't get a lot of cooking done: the programming isn't appropriate for a microwave.

So how could a 46 chromosome human being become a 64 chromosome horse? As you've guessed, it wouldn't be easy, but the key lies within a process called morphogenesis. This is the biological process by which an organism achieves its gross structure. It's what goes on in the womb: we all know about the fertilised egg dividing and replicating, but that just gives you a great big blob. How does this system go on to define different cell types and a specific skeletal structure; muscles attached in the right places; a supporting organ structure to make it work; a nerve network and a brain to control the process?

In morphogenesis, certain genes (DNA encoded instructions, remember?) are called Master Regulatory Genes. These cause cells to create morphogens, molecules which carry the master building commands to other cells and initiate secondary regulatory genes - you might think of them as subroutines in a computer program. Every DNA strand holds an identical program, but not every cell is running the same routine from this program: we have now differentiated into different cell types. Free-lance cells that may become different types of cell are known as stem-cells by the way.

Different cells can organise themselves in the womb by differential adhesion, a process by which cells will only adhere to one another if they recognise each other as a similar type. Another process called _gastrulation_ allows clumps of stem-cells to switch off this adhesion and migrate to different areas, then establish a new building site. At all points, the DNA master plan is available as a reference guide, so these migrant clusters know when they've hit target.

This is a gross over-simplification of what goes on, but we can use this as a basis to formulate a hypothetical method by which an adult human might change into a different animal. If we look back at the software analogy then what we want is a clever piece of programming that will take the pocket calculator software and rewrite it into microwave oven software, like the sort of update software Windows is always running while you're trying to do something important on your desktop (No, I don't want to reboot now, dammit!).

So, how should our updater work?

Well, the updater would be a sort of temporary DNA that operates like, and in fact would actually be, a virus. A virus invades a cell, reprograms the existing DNA, and forces the cell to do something different. In this case, the updater would initiate morphogenesis. As understatements go, that's a biggie, but it is possible and occurs in nature: consider tadpoles and frogs. The now-dormant mechanisms of foetal development must be reinitiated, but in slightly different form. We would essentially be convincing the body that it was in fact an embryonic horse.

We need to alter all the cells in the body, and we don't want trouble from the immune system. We can't just turn the immune system off: that would render the subject instantly vulnerable to any germ they were harbouring within their body. This sort of transformation isn't going to happen overnight: it will take months, so first off the updater must introduce itself as "friendly software": we want it to work with the body, not against it.

We also need a lot of stem-cells. Stem-cells in an adult body are rare and much more restricted than those in the womb, but if the right genes are tweaked, cells can be reverted into stem-cells. There is a lot of research into how to do this at the moment.

We need lots of raw material, but that isn't a problem: the updater will start by converting the subject into a human-massed horse (let's call it a foal), and program in either normal equine growth or an accelerated program: we'll have a tonne of oats to go, please.

We need to limit the process. This is critical. A major headache for geneticists at the moment is the unregulated growth of stem-cells into tumours. Our stem-cells have to known when to stop replicating; to stop changing things.

And finally, we want our updater virus to delete itself when complete and leave each and every cell with equine DNA in it.

This process is a tall order. It will take an incredibly thorough understanding of how genetics works. The gene code is not a simple one: many nucleotides control more than one trait in the body. Our understanding of morphogenesis is in its most rudimentary stages. There is much incentive to increase our knowledge though. This is Topic Of The Century as far as medicine goes. Only a few weeks before I wrote this scientists announced they can now genetically reactivate muscular healing in the elderly - a function that the body usually turns off as we get older. There is much speculation that a body could be coaxed to repair a damaged spine, or re-grow a severed limb; even keep itself biologically young indefinitely.

Interestingly there is also much research into equine DNA: there's a fantastic profit to be made by the organisation that can engineer a faster race-horse, or make the modern race-horse into a hardier creature.

Will we ever see this happen? Well, maybe. Ultimately, I believe DNA engineering might become the preserve of a new form of artist, using software to improve new life-forms. Humans have a long precedent of wishing to change or improve their own bodies. While the initial research will cost billions, the final technology shouldn't be too expensive. Tastes and attitudes do change quite radically over time, and it may be the case that in fifty years, the new trend will be to custom design your body into whatever you wish. Well, we can hope!

Genetics Home Reference What is DNA? A simple explanation.
Learn Genetics An excellent animated tutorial on genetics and stem cells from the University of Utah.
Wikipedia Entry on Morphogenesis.

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